Chapter 1

SLAU284F – August 2012 – Revised March 2018

USB Module

NOTE: This chapter is an excerpt from the MSP430x5xx and MSP430x6xx Family User's Guide.

This chapter describes the USB module that is available in some devices.

Topic ........................................................................................................................... Page

1.1 USB Introduction ................................................................................................. 2

1.2 USB Operation..................................................................................................... 4
1.3 USB Transfers ................................................................................................... 15
1.4 USB Registers ................................................................................................... 22

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1.1 USB Introduction

The features of the USB module include:
• Fully compliant with the USB 2.0 full-speed specification
– Full-speed device (12 Mbps) with integrated USB transceiver (PHY)
– Up to eight input and eight output endpoints
– Supports control, interrupt, and bulk transfers
– Supports USB suspend, resume, and remote wakeup
• A power supply system independent from the PMM system
– Integrated 3.3-V LDO regulator with sufficient output to power entire MSP430 and system circuitry
from 5-V VBUS
– Integrated 1.8-V LDO regulator for PHY and PLL
– Easily used in either bus-powered or self-powered operation
– Current-limiting capability on 3.3-V LDO output
– Autonomous power-up of device on arrival of USB power possible (low or no battery condition)
• Internal 48-MHz USB clock
– Integrated programmable PLL
– Highly-flexible input clock frequencies for use with lowest-cost crystals
• 1904 bytes of dedicated USB buffer space for endpoints, with fully configurable size to a granularity of
eight bytes
• Timestamp generator with 62.5-ns resolution
• When USB is disabled
– Buffer space is mapped into general RAM, providing additional 2KB to the system
– USB interface pins become high-current general purpose I/O pins

NOTE: Use of the word device

The word device is used throughout the chapter. This word can mean one of two things,
depending on the context. In a USB context, it means what the USB specification refers to as
a device, function, or peripheral; that is, a piece of equipment that can be attached to a USB
host or hub. In a semiconductor context, it refers to an integrated circuit such as the
MSP430.
To avoid confusion, the term USB device in this document refers to the USB-context
meaning of the word. The word device by itself refers to silicon devices such as the MSP430.

Figure 1-1 shows a block diagram of the USB module.

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System VCORE All USB digital logic power

System RAM
VUSB

USB Power System

3.3 V 1.8 V
VBUS LDO LDO PLL power

PHY power

PUR USB Engine

Transceiver
D+ Serial Interface
(PHY) USB
Engine (SIE)
Buffer
D– RAM
USB Buffer
Manager (UBM)
XT1 clock source
48 MHz PLL
XT2 clock source USB Control Registers

Timerstamp
TSEn Generator

USB Timer

Figure 1-1. USB Block Diagram

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1.2 USB Operation

The USB module is a comprehensive full-speed USB device compliant with the USB 2.0 specification.
The USB engine coordinates all USB-related traffic. It consists of the USB SIE (serial interface engine)
and USB Buffer Manager (UBM). All traffic received on the USB receive path is de-serialized and placed
into receive buffers in the USB buffer RAM. Data in the buffer RAM marked 'ready to be sent' are
serialized into packets and sent to the USB host.
The USB engine requires an accurate 48-MHz clock to sample the incoming data stream. This is
generated by a PLL that is fed from one of the system oscillators (XT1 or XT2). A crystal of 4 MHz or
greater is required. In addition to crystal operation, the crystal bypass mode can also be used to supply
the clock required by the PLL. The PLL is very flexible and can adapt to a wide range of crystal and input
frequencies, allowing for cost-effective clock designs.

NOTE: The reference clock to the PLL depends on the device configuration. On devices that contain
the optional XT2, the reference clock to the PLL is XT2CLK, regardless of whether or not
XT1 is available. If the device has only XT1, then the reference is XT1CLK. See the device-
specific data sheet for clock sources available.

NOTE: The USB module only supports active operation during power modes AM through LPM1.

The USB buffer memory is where data is exchanged between the USB interface and the application
software. It is also where the usage of endpoints 1 to 7 are defined. This buffer memory is implemented
such that it can be easily accessed like RAM by the CPU or DMA while USB module is not in suspend
condition.

1.2.1 USB Transceiver (PHY)

The physical layer interface (USB transceiver) is a differential line driver directly powered from VUSB (3.3
V). The line driver is connected to the DP and DM pins, which form the signaling mechanism of the USB
interface.
When the PUSEL bit is set, DP and DM are configured to function as USB drivers controlled by the USB
core logic. When the bit is cleared, these two pins become "Port U", which is a pair of high-current general
purpose I/O pins. In this case, the pins are controlled by the Port U control registers. Port U is powered
from the VUSB rail, separate from the main device DVCC. If these pins are to be used, whether for USB
or general purpose use, it is necessary that VUSB be properly powered from either the internal regulators
or an external source.

1.2.1.1 D+ Pullup Via PUR Pin

When a full-speed USB device is attached to a USB host, it must pull up the D+ line (DP pin) for the host
to recognize its presence. The MSP430 USB module implements this with a software-controlled pin that
activates a pullup resistor. The bit that controls this function is PUR_EN. If software control is not desired,
the pullup can be connected directly to VUSB.

1.2.1.2 Shorts on Damaged Cables and Clamping

USB devices must tolerate connection to a cable that is damaged, such that it has developed shorts on
either ground or VBUS. The device should not become damaged by this event, either electrically or
physically. To this end, the MSP430 USB power system features a current limitation mechanism that limits
the available transceiver current in the event of a short to ground. The transceiver interface itself therefore
does not need a current limiting function.
Note that if VUSB is to be powered from a source other than the integrated regulator, the absence of
current-limiting in the transceiver means that the external power source must itself be tolerant of this same
shorting event, through its own means of current limiting.

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1.2.1.3 Port U Control

When PUSEL is cleared, the Port U pins (PU.0 and PU.1) function as general-purpose, high-current I/O
pins. These pins can only be configured together as either both inputs or both outputs. Port U is supplied
by the VUSB rail. If the 3.3-V LDO is not being used in the system (disabled), the VUSB pin can be
supplied externally.
PUOPE controls the enable of both outputs residing on the Port U pins. Setting PUIPE =1 causes both
input buffers to be enabled. When Port U outputs are enabled (PUOPE = 1), the PUIN0 and PUIN1 pins
mirror what is present on the outputs assuming PUIPE = 1. To use the Port U pins as inputs, the outputs
should be disabled by setting PUOPE = 0, and enabling the input buffers by setting PUIPE = 1. Once
configured as inputs (PUIPE = 1), the PUIN0 and PUIN1 bits can be read to determine the respective
input values.
When PUOPE is set, both Port U pins function as outputs, controlled by PUOUT0 and PUOUT1. When
driven high, they use the VUSB rail, and they are capable of a drive current higher than other I/O pins on
the device. See the device-specific datasheet for parameters.
By default, PUOPE and PUIPE are cleared. PU.0 and PU.1 are high-impedance (input buffers are
disabled and outputs are disabled).

1.2.2 USB Power System

The USB power system incorporates dual LDO regulators (3.3 V and 1.8 V) that allow the entire MSP430
device to be powered from 5-V VBUS when it is made available from the USB host. Alternatively, the
power system can supply power only to the USB module, or it can be unused altogether, as in a fully self-
powered device. The block diagram is shown in Figure 1-2.
VUSB V18

Overload
VBUS 3.3 V LDO Detection 1.8 V LDO

USB Low
BOR Detection

VBONIFG
“VBUS present" SLDOEN
interrupt VUSBEN
VBONIE
USBBGVBV
VBOFFIFG LDOOVLIFG
"VBUS removed” "VBUS overload"
interrupt interrupt
VBOFFIE LDOOVLIE PHY Power PHY, PLL Power

Figure 1-2. USB Power System

The 3.3-V LDO receives 5 V from VBUS and provides power to the transceiver, as well as the VUSB pin.
Using this setup prevents the relatively high load of the transceiver and PLL from loading a local system
power supply, if used. Thus it is very useful in battery-powered devices.
The 1.8-V LDO receives power from the VUSB pin – which is to be sourced either from the internal 3.3-V
LDO or externally – and provides power to the USB PLL and transceiver. The 1.8-V LDO in the USB
module is not related to the LDO that resides in the MSP430 Power Management Module (PMM).
The inputs and outputs of the LDOs are shown in Figure 1-2. VBUS, VUSB, and V18 need to be
connected to external capacitors. The V18 pin is not intended to source other components in the system,
rather it exists solely for the attachment of a load capacitor.

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1.2.2.1 Enabling and Disabling

The 3.3-V LDO is enabled or disabled by setting or clearing VUSBEN, respectively. Even if enabled, if the
voltage on VBUS is detected to be low or nonexistent, the LDO is suspended. No additional current is
consumed while the LDO is suspended. When VBUS rises above the USB power brownout level, the LDO
reference and low voltage detection become enabled. When VBUS rises further above the launch voltage
VLAUNCH, the LDO module becomes enabled (see Figure 1-3). See device-specific data sheet for value of
VLAUNCH.
VBUS
VBUS

VLAUNCH
VUSB

Time
tENABLE

Figure 1-3. USB Power Up and Down Profile

The 1.8-V LDO can be enabled or disabled by setting SLDOEN accordingly. By default, the 1.8-V LDO is
controlled automatically according to whether power is available on VBUS. This auto-enable feature is
controlled by SLDOAON. In this case, that the SLDOEN bit does not reflect the state of the 1.8-V LDO. If
the user wishes to know the state while using the auto-enable feature, the USBBGVBV bit in
USBPWRCTL can be read. In addition, to disable the 1.8-V LDO, SLDOAON must be cleared along with
SLDOEN. If providing VUSB from an external source, rather than through the integrated 3.3-V LDO, keep
in mind that if 5 V is not present on VBUS, the 1.8-V LDO is not automatically enabled. In this situation,
either VBUS much be attached to USB bus power, or the SLDOAON bit must be cleared and SLDOEN
set.
It is required that power from the USB cable's VBUS be directed through a Schottky diode prior to entering
the VBUS terminal. This prevents current from draining into the cable's VBUS from the LDO input,
allowing the MSP430 to tolerate a suspended or unpowered USB cable that remains electrically
connected.
The VBONIFG flag can be used to indicate that the voltage on VBUS has risen above the launch voltage.
In addition to the VBONIFG being set, an interrupt is also generated when VBONIE = 1. Similarly, the
VBOFFIFG flag can be used to indicate that the voltage on VBUS has fallen below the launch voltage. In
addition to the VBOFFIFG being set, an interrupt is also generated when VBOFFIE = 1. The USBBGVBV
bit can also be polled to indicate the level of VBUS; that is, above or below the launch voltage.

1.2.2.2 Powering the Rest of the MSP430 From USB Bus Power Via VUSB
The output of the 3.3-V LDO can be used to power the entire MSP430 device, sourcing the DVCC rail. If
this is desired, the VUSB and DVCC should be connected externally. Power from the 3.3-V LDO is
sourced into DVCC (see Figure 1-4).

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External Connection

VUSB DVCC

3.3 V 1.8 V VCORE

VBUS PMM
LDO LDO

I/Os

USB USB Digital

Transceiver Core

USB PLL

USB Power Domain MSP430 DVCC Power Domain

Figure 1-4. Powering Entire MSP430 From VBUS

With this connection made, the MSP430 allows for autonomous power up of the device when VBUS rises
above VLAUNCH. If no voltage is present on VCORE – meaning the device is unpowered (or, in LPMx.5
mode) – then both the 3.3-V and 1.8-V LDOs automatically turn on when VBUS rises above VLAUNCH.
Note that if DVCC is being driven from VUSB in this manner, and if power is available from VUSB,
attempting to place the device into LPMx.5 results in the device immediately re-powering. This is because
it re-creates the conditions of the autonomous feature described above (no VCORE but power available on
VBUS). The resulting drop of VCORE would cause the system to immediately power up again.
When DVCC is being powered from VUSB, it is up to the user to ensure that the total current being drawn
from VBUS stays below IDET.

1.2.2.3 Powering Other Components in the System from VUSB

There is sufficient current capacity available from the 3.3-V LDO to power not only the entire MSP430 but
also other components in the system, via the VUSB pin.
If the device is to always be connected to USB, then perhaps no other power system is needed. If it only
occasionally connects to USB and is battery-powered otherwise, then sourcing system power via the 3.3-V
LDO takes power burden away from the battery. Alternatively, if the battery is rechargeable, the
recharging can be driven from VUSB.

1.2.2.4 Self-Powered Devices

Some applications may be self-powered, in that the VUSB power is supplied externally. In these cases,
the 3.3-V LDO would be disabled (VUSBEN = 0). For proper USB operation, the voltage on VBUS can still
be detected, even while the 3.3-V LDO disabled, by setting USBDETEN = 1. When VBUS rises above the
USB power brownout level, low voltage detection becomes enabled. When VBUS rises further above the
launch voltage VLAUNCH, the voltage on VBUS is detected.

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1.2.2.5 Current Limitation and Overload Protection

The 3.3-V LDO features current limitation to protect the transceiver during shorted-cable conditions. A
short or overload condition – that is, when the output of the LDO becomes current-limited to IDET. This is
reported to software via the VUOVLIFG flag. See device-specific data sheet for value of IDET.
If this event occurs, it means USB operation may become unreliable, due to insufficient power supply. As
a result, software may wish to cease USB operation. If the OVLAOFF bit is set, USB operation is
automatically terminated by clearing VUSBEN.
During overload conditions, VUSB and V18 drop below their nominal output voltage. In power scenarios
where DVCC is exclusively supplied from VUSB, repetitive system restarts may be triggered as long the
short or overload condition exists. For this reason, firmware should avoid re-enabling USB after detection
of an overload on the previous power session, until the cause of failure can be identified. Ultimately, it is
the user's responsibility to ensure that the current drawn from VBUS does not exceed IDET.
The VUOVLIFG flag can be used to indicate an overcurrent condition on the 3.3-V LDO. When an
overcurrent condition is detected, VUOVLIFG = 1. In addition to the VUOVLIFG being set, an interrupt is
also generated when VUOVLIE = 1.
The USB power system brownout circuit is supplied from VBUS or DVCC, whichever carries the higher
voltage.

1.2.3 USB Phase-Locked Loop (PLL)

The PLL provides the low-jitter high-accuracy clock needed for USB operation (see Figure 1-5).
UPMB
6
UPQB
/M
UCLKSEL
3
†
PLL reference clock Charge Loop 2
/Q PFD Pump VCO
Filter
00
reserved 01 USBCLK
reserved 10
11
†
XT2CLK on devices with XT2, otherwise XT1CLK. UPLLEN

Figure 1-5. USB-PLL Analog Block Diagram

The reference clock to the PLL depends on the device configuration. On devices that contain the optional
XT2, the reference clock to the PLL is XT2CLK, regardless if XT1 is available. If the device has only XT1,
then the reference is XT1CLK. A four-bit prescale counter controlled by the UPQB bits allows division of
the reference to generate the PLL update clock. The UPMB bits control the divider in the feedback path
and define the multiplication rate of the PLL (see Equation 1).
CLKSEL
fOUT = CLKSEL × DIVM with = fUPD ³ 1.5 MHz
DIVQ DIVQ (1)
Where
CLKSEL is the PLL reference clock frequency
DIVQ is derived from Table 1-1
DIVM represents the value of UPMB field
Table 1-2 lists some common clock input frequencies for CLKSEL, along with the appropriate register
settings for generating the nominal 48-MHz clock required by the USB serial engine. For crystal operation,
a 4 MHz or higher crystal is required. For crystal bypass mode of operation, 1.5 MHz is the lowest external
clock input possible for CLKSEL.

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If USB operation is used in a bus-powered configuration, disabling the PLL is necessary to pass the USB
requirement of not consuming more than 500 µA. The UPLLEN bit enables or disables the PLL. The
PFDEN bit must be set to enable the phase and frequency discriminator. Out-of-lock, loss-of-signal, and
out-of-range are indicated and flagged in the interrupt flags OOLIFG, LOSIFG, OORIFG, respectively.

NOTE: UCLKSEL bits should always be cleared, which is the default operation. All other
combinations are reserved for future usages.

Table 1-1. USB-PLL Pre-Scale Divider

UPQB DIVQ
000 1
001 2
010 3
011 4
100 6
101 8
110 13
111 16

Table 1-2. Register Settings to Generate 48 MHz Using Common Clock Input Frequencies
CLKLOOP UPLLCLK ACCURACY
CLKSEL (MHz) UPQB UPMB DIVQ DIVM
(MHz) (MHz) (ppm)
1.5 000 011111 1 32 1.5 48 0
1.6 000 011101 1 30 1.6 48 0
1.7778 000 011010 1 27 1.7778 48 0
1.8432 000 011001 1 26 1.8432 47.92 -1570
1.8461 000 011001 1 26 1.8461 48 0
1.92 000 011000 1 25 1.92 48 0
2 000 010111 1 24 2 48 0
2.4 000 010011 1 20 2.4 48 0
2.6667 000 010001 1 18 2.6667 48 0
3 000 001111 1 16 3 48 0
3.2 001 011110 2 30 1.6 48 0
3.5556 001 011010 2 27 1.7778 48 0
3.84 001 011001 2 25 1.92 48 0
(1)
4 001 010111 2 24 2 48 0
4.1739 001 010110 2 23 2.086 48 0
4.3636 001 010101 2 22 2.1818 48 0
4.5 010 011111 3 32 1.5 48 0
4.8 001 010011 2 20 2.4 48 0
5.33 ≉ (16/3) 001 010001 2 18 2.6667 48 0
5.76 010 011000 3 25 1.92 48 0
6 010 010111 3 24 2 48 0
6.4 011 011101 4 30 1.6 48 0
7.2 010 010011 3 20 2.4 48 0
7.68 011 011000 4 25 1.92 48 0
8 (1) 010 010001 3 18 2.6667 48 0
9 010 001111 3 16 3 48 0

(1)
This frequency can be automatically detected by the factory-supplied BSL, for use in production programming of the MSP430 via
USB. See MSP430 Programming With the Bootloader (BSL) for details.

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Table 1-2. Register Settings to Generate 48 MHz Using Common Clock Input
Frequencies (continued)
CLKLOOP UPLLCLK ACCURACY
CLKSEL (MHz) UPQB UPMB DIVQ DIVM
(MHz) (MHz) (ppm)
9.6 011 010011 4 20 2.4 48 0
10.66 ≉ (32/3) 011 010001 4 18 2.6667 48 0
12 (1) 011 001111 4 16 3 48 0
12.8 101 011101 8 30 1.6 48 0
14.4 100 010011 6 20 2.4 48 0
16 100 010001 6 18 2.6667 48 0
16.9344 100 010000 6 17 2.8224 47.98 -400
16.94118 100 010000 6 17 2.8235 48 0
18 100 001111 6 16 3 48 0
19.2 101 010011 8 20 2.4 48 0
24 (1) 101 001111 8 16 3 48 0
25.6 111 011101 16 30 1.6 48 0
26.0 110 010111 13 24 2 48 0
32 111 010111 16 24 2.6667 48 0

1.2.3.1 Modifying the Divider Values

Updating the values of UPQB (DIVQ) and UPMB (DIVM) to select the desired PLL frequency must occur
simultaneously to avoid spurious frequency artifacts. The values of UPQB and UPMB can be calculated
and written to their buffer registers; the final update of UPQB and UPMB occurs when the upper byte of
UPLLDIVB (UPQB) is written.

1.2.3.2 PLL Error Indicators

The PLL can detect three kinds of errors. Out-of-lock (OOL) is indicated if a frequency correction is
performed in the same direction (that is, up or down) for four consecutive update periods. Loss-of-signal
(LOS) is indicated if a frequency correction is performed in the same direction (that is, up or down) for 16
consecutive update periods. Out-of-range (OOR) is indicated if PLL was unable to lock for more than 32
update periods.
OOL, LOS, and OOR trigger their respective interrupt flags (USBOOLIFG, USBLOSIFG, USBOORIFG) if
errors occur, and interrupts are generated if enabled by their enable bits (USBOOLIE, USBLOSIE,
USBOORIE).

1.2.3.3 PLL Startup Sequence

To achieve the fastest startup of the PLL, the following sequence is recommended.
1. Enable VUSB and V18.
2. Wait 2 ms for external capacitors to charge, so that proper VUSB is in place. (During this time, the
USB registers and buffers can be initialized.)
3. Activate the PLL, using the required divider values.
4. Wait 2 ms and check PLL. If it stays locked, it is ready to be used.

1.2.4 USB Controller Engine

The USB controller engine transfers data packets arriving from the USB host into the USB buffers, and
also transmits valid data from the buffers to the USB host. The controller engine has dedicated, fixed
buffer space for input endpoint 0 and output endpoint 0, which are the default USB endpoints for control
transfers.

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The 14 remaining endpoints (seven input and seven output) may have one or more USB buffers assigned
to them. All the buffers are located in the USB buffer memory. This memory is implemented as "multiport"
memory, in that it can be accessed both by the USB buffer manager and also by the CPU and DMA.
Each endpoint has a dedicated set of descriptor registers that describe the use of that endpoint (see
Figure 1-6). Configuration of each endpoint is performed by setting its descriptor registers. These data
structures are located in the USB buffer memory and contain address pointers to the next memory buffer
for receive or transmit.
Assigning one or two data buffers to an endpoint, of up to 64 bytes, requires no further software
involvement after configuration. If more than two buffers per endpoint are desired, however, software must
change the address pointers on the fly during a receive or transmit process.
Synchronization of empty and full buffers is done using validation flags. All events are indicated by flags
and fire a vector interrupt when enabled. Transfer event indication can be enabled separately.
EP0 to EP7 EP0 to EP7

-
Y Y
Flag X Flag X Y-Buffer Y'-Buffer Y''-Buffer
Pointer Pointer (64 bytes) (64 bytes) (64 bytes)

Counter Y-Buffer Counter

(64 bytes)
Config EPn Config EPn

X-Buffer X-Buffer X'-Buffer X''-Buffer

(64 bytes) (64 bytes) (64 bytes) (64 bytes)

Figure 1-6. Data Buffers and Descriptors

1.2.4.1 USB Serial Interface Engine (SIE)

The SIE logic manages the USB packet protocol requirements for the packets being received and
transmitted on the bus. For packets being received, the SIE decodes the packet identifier field (packet ID)
to determine the type of packet being received and to ensure the packet ID is valid. For token and data
packets being received, the SIE calculates the packet cycle redundancy check (CRC) and compares the
value to the CRC contained in the packet to verify that the packet was not corrupted during transmission.
For token and data packets being transmitted, the SIE generates the CRC that is transmitted with the
packet. For packets being transmitted, the SIE also generates the synchronization field (SYNC), which is
an eight-bit field at the beginning of each packet. In addition, the SIE generates the correct packet ID for
all packets being transmitted.
Another major function of the SIE is the overall serial-to-parallel conversion of the data packets being
received or transmitted.

1.2.4.2 USB Buffer Manager (UBM)

The USB buffer manager provides the control logic that interfaces the SIE to the USB endpoint buffers.
One of the major functions of the UBM is to decode the USB device address to determine if the USB host
is addressing this particular USB device. In addition, the endpoint address field and direction signal are
decoded to determine which particular USB endpoint is being addressed. Based on the direction of the
USB transaction and the endpoint number, the UBM either writes or reads the data packet to or from the
appropriate USB endpoint data buffer.

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The TOGGLE bit for each output endpoint configuration register is used by the UBM to track successful
output data transactions. If a valid data packet is received and the data packet ID matches the expected
packet ID, the TOGGLE bit is toggled. Similarly, the TOGGLE bit for each input endpoint configuration is
used by the UBM to track successful input data transactions. If a valid data packet is transmitted, the
TOGGLE bit is toggled. If the TOGGLE bit is cleared, a DATA0 packet ID is transmitted in the data packet
to the host. If the TOGGLE bit is set, a DATA1 packet ID is transmitted in the data packet to the host. See
Section 1.3 regarding details of USB transfers.

1.2.4.3 USB Buffer Memory

The USB buffer memory contains the data buffers for all endpoints and for SETUP packets. In that the
buffers for endpoints 1 to 7 are flexible, there are USB buffer configuration registers that define them, and
these too are in the USB buffer memory. (Endpoint 0 is defined with a set of registers in the USB control
register space.) Storing these in open memory allows for efficient, flexible use, which is advantageous
because use of these endpoints is very application-specific.
This memory is implemented as "multiport" memory, in that it can be accessed both by the USB buffer
manager and also by the CPU and DMA. The SIE allows CPU or DMA access, but reserves priority. As a
result, CPU or DMA access is delayed using wait states if a conflict arises with an SIE access.
When the USB module is disabled (USBEN = 0), the buffer memory behaves like regular RAM. When
changing the state of the USBEN bit (enabling or disabling the USB module), the USB buffer memory
should not be accessed within four clocks before and eight clocks after changing this bit, as doing so
reconfigures the access method to the USB memory.
Accessing of the USB buffer memory by CPU or DMA is only possible if the USB PLL is active. When a
host requests suspend condition the application software (for example, USB stack) of client has to switch
off the PLL within 10 ms. Note that the MSP430 USB suspend interrupt occurs around 5 ms after the host
request.
Each endpoint is defined by a block of six configuration "registers" (based in RAM, they are not true
registers in the strict sense of the word). These registers specify the endpoint type, buffer address, buffer
size and data packet byte count. They define an endpoint buffer space that is 1904 bytes in size. An
additional 24 bytes are allotted to three remaining blocks – the EP0_IN buffer, the EP0_OUT buffer, and
the SETUP packet buffer (see Table 1-3).

Table 1-3. USB Buffer Memory Map

Address
Memory Short Form Access Type
Offset
Start of buffer space STABUFF Read/Write 0000h
1904 bytes of configurable buffer space ⋮ Read/Write ⋮
End of buffer space TOPBUFF Read/Write 076Fh
Read/Write 0770h
Output endpoint_0 buffer USBOEP0BUF Read/Write ⋮
Read/Write 0777h
Read/Write 0778h
Input endpoint_0 buffer USBIEP0BUF Read/Write ⋮
Read/Write 077Fh
Read/Write 0780h
Setup Packet Block USBSUBLK Read/Write ⋮
Read/Write 0787h

Software can configure each buffer according to the total number of endpoints needed. Single or double
buffering of each endpoint is possible.
Unlike the descriptor registers for endpoints 1 to 7, which are defined as memory entries in USB RAM,
endpoint 0 is described by a set of four registers (two for output and two for input) in the USB control
register set. Endpoint 0 has no base-address register, since these addresses are hardwired. The bit
positions have been preserved to provide consistency with endpoint_n (n = 1 to 7).

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1.2.4.4 USB Fine Timestamp

The USB module is capable of saving a timestamp associated with particular USB events (see Figure 1-
7). This can be useful in compensating for delays in software response. The timestamp values are based
on the USB module's internal timer, driven by USBCLK.
Up to four events can be selected to generate the timestamp, selected with the TSESEL bits. When they
occur, the value of the USB timer is transferred to the timestamp register USBTSREG, and thus the exact
moment of the event is recorded. The trigger options include one of three DMA channels, or a software-
driven event. The USB timer cannot be directly accessed by reading.
Furthermore, the value of the USB timer can be used to generate periodic interrupts. Since the USBCLK
can have a frequency different from the other system clocks, this gives another option for periodic system
interrupts. The UTSEL bits select the divider from the USB clock. UTIE must be set for an interrupt vector
to get triggered.
The timestamp register is set to zero on a frame-number-receive event and pseudo-start-of-frame.
TSGEN enables or disables the time stamp generator.
TSESEL

2
UTSEL
TSE0 00
TSE1 01 16-Bit Time Stamp Register (read only)
3
TSE2 10
TSE3 11 000 UTIE
001
010
VECINT
011
100 UTIFG
101
110
111

USBCLK
/3 16-Bit USB Timer (not accessible)
(48 MHz)
TSGEN
Frame Number Received Reset to 0
Reset
(of USB Configuration Registers)

Figure 1-7. USB Timer and Time Stamp Generation

1.2.4.5 Suspend and Resume Logic

The USB suspend and resume logic detects suspend and resume conditions on the USB bus. These
events are flagged in SUSRIFG and RESRIFG, respectively, and they fire dedicated interrupts, if the
interrupts are enabled (SUSRIE and RESRIE).
The remote wakeup mechanism, in which a USB device can cause the USB host to awaken and resume
the device, is triggered by setting the RWUP bit of the USBCTL register.
See Section 1.2.6 for more information.

1.2.4.6 Reset Logic

A PUC resets the USB module logic. When FRSTE = 1, the logic is also reset when a USB reset event
occurs on the bus, triggered from the USB host. (A USB reset also sets the RSTRIFG flag.) USB buffer
memory is not reset by a USB reset.

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1.2.5 USB Vector Interrupts

The USB module uses a single interrupt vector generator register to handle multiple USB interrupts. All
USB-related interrupt sources trigger the USBVECINT (also called USBIV) vector, which then contains a
6-bit vector value that identifies the interrupt source. Each of the interrupt sources results in a different
offset value read. The interrupt vector returns zero when no interrupt is pending.
Reading the interrupt vector register clears the corresponding interrupt flag and updates its value. The
interrupt with highest priority returns the value 0002h; the interrupt with lowest priority returns the value
003Eh when reading the interrupt vector register. Writing to this register clears all interrupt flags.
For each input and output endpoints resides an USB transaction interrupt indication enable. Software may
set this bit to define if interrupts are to be flagged in general. To generate an interrupt the corresponding
interrupt enable and flag must be set.

Table 1-4. USB Interrupt Vector Generation

USBVECINT
Interrupt Source Interrupt Flag Bit Interrupt Enable Bit Indication Enable Bit
Value
0000h no interrupt – – –
0002h USB-PWR drop ind. USBPWRCTL.VUOVLIFG USBPWRCTL.VUOVLIE –
0004h USB-PLL lock error USBPLLIR.USBPLLOOLIFG USBPLLIR.USBPLLOOLIE –
0006h USB-PLL signal error USBPLLIR.USBPLLOSIFG USBPLLIR.USBPLLLOSIE –
0008h USB-PLL range error USBPLLIR.USBPLLOORIFG USBPLLIR.USBPLLOORIE –
000Ah USB-PWR VBUS-on USBPWRCTL.VBONIFG USBPWRCTL.VBONIE –
000Ch USB-PWR VBUS-off USBPWRCTL.VBOFFIFG USBPWRCTL.VBOFFIE –
000Eh reserved – – –
0010h USB timestamp event USBMAINTL.UTIFG USBMAINTL.UTIE –
0012h Input Endpoint-0 USBIEPIFG.EP0 USBIEPIE.EP0 USBIEPCNFG_0.USBIIE
0014h Output Endpoint-0 USBOEPIFG.EP0 USBOEPIE.EP0 USBOEPCNFG_0.USBIIE
0016h RSTR interrupt USBIFG.RSTRIFG USBIE.RSTRIE –
0018h SUSR interrupt USBIFG.SUSRIFG USBIE.SUSRIE –
001Ah RESR interrupt USBIFG.RESRIFG USBIE.RESRIE –
001Ch reserved – – –
001Eh reserved – – –
0020h Setup packet received USBIFG.SETUPIFG USBIE.SETUPIE –
0022h Setup packet overwrite USBIFG.STPOWIFG USBIE.STPOWIE –
0024h Input Endpoint-1 USBIEPIFG.EP1 USBIEPIE.EP1 USBIEPCNF_1.USBIIE
0026h Input Endpoint-2 USBIEPIFG.EP2 USBIEPIE.EP2 USBIEPCNF_2.USBIIE
0028h Input Endpoint-3 USBIEPIFG.EP3 USBIEPIE.EP3 USBIEPCNF_3.USBIIE
002Ah Input Endpoint-4 USBIEPIFG.EP4 USBIEPIE.EP4 USBIEPCNF_4.USBIIE
002Ch Input Endpoint-5 USBIEPIFG.EP5 USBIEPIE.EP5 USBIEPCNF_5.USBIIE
002Eh Input Endpoint-6 USBIEPIFG.EP6 USBIEPIE.EP6 USBIEPCNF_6.USBIIE
0030h Input Endpoint-7 USBIEPIFG.EP7 USBIEPIE.EP7 USBIEPCNF_7.USBIIE
0032h Output Endpoint-1 USBOEPIFG.EP1 USBOEPIE.EP1 USBOEPCNF_1.USBIIE
0034h Output Endpoint-2 USBOEPIFG.EP2 USBOEPIE.EP2 USBOEPCNF_2.USBIIE
0036h Output Endpoint-3 USBOEPIFG.EP3 USBOEPIE.EP3 USBOEPCNF_3.USBIIE
0038h Output Endpoint-4 USBOEPIFG.EP4 USBOEPIE.EP4 USBOEPCNF_4.USBIIE
003Ah Output Endpoint-5 USBOEPIFG.EP5 USBOEPIE.EP5 USBOEPCNF_5.USBIIE
003Ch Output Endpoint-6 USBOEPIFG.EP6 USBOEPIE.EP6 USBOEPCNF_6.USBIIE
003Eh Output Endpoint-7 USBOEPIFG.EP7 USBOEPIE.EP7 USBOEPCNF_7.USBIIE

1.2.6 Power Consumption

USB functionality consumes more power than is typically drawn in the MSP430. Since most MSP430
applications are power sensitive, the MSP430 USB module has been designed to protect the battery by
ensuring that significant power load only occurs when attached to the bus, allowing power to be drawn
from VBUS.

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The two components of the USB module that draw the most current are the transceiver and the PLL. The
transceiver can consume large amounts of power while transmitting, but in its quiescent state – that is,
when not transmitting data – the transceiver actually consumes very little power. This is the amount
specified as IIDLE. This amount is so little that the transceiver can be kept active during suspend mode
without presenting a problem for bus-powered applications. Fortunately the transceiver always has access
to VBUS power when drawing the level of current required for transmitting.
The PLL consumes a larger amount of current. However, it need only be active while connected to the
host, and the host can supply the power. When the PLL is disabled (for example, during USB suspend),
USBCLK automatically is sourced from the VLO.

1.2.7 Suspend and Resume

All USB devices must support the ability to be suspended into a no-activity state, and later resumed.
When suspended, a device is not allowed to consume more than 500uA from the USB's VBUS power rail,
if the device is drawing any power from that source. A suspended device must also monitor for a resume
event on the bus.
The host initiates a suspend condition by creating a constant idle state on the bus for more than 3.0 ms. It
is the responsibility of the software to ensure the device enters its low power suspend state within 10 ms
of the suspend condition. The USB specification requires that a suspended bus-powered USB device not
draw in excess of 500 µA from the bus.

1.2.7.1 Entering Suspend

When the host suspends the USB device, a suspend interrupt is generated (SUSRIFG). From this point,
the software has 10 ms to ensure that no more than 500uA is being drawn from the host via VBUS.
For most applications, the integrated 3.3-V LDO is being used. In this case, the following actions should
be taken:
• Disable the PLL by clearing UPLLEN (UPLLEN = 0)
• Limit all current sourced from VBUS that causes the total current sourced from VBUS equal to 500 µA
minus the suspend current, ISUSPEND (see the device-specific data sheet).
Disabling the PLL eliminates the largest on-chip draw of power from VBUS. During suspend, the USBCLK
is automatically sourced by the VLO (VLOCLK), allowing the USB module to detect resume when it
occurs. It is a good idea to also then ensure that the RESRIE bit is also set, so that an interrupt is
generated when the host resumes the device. If desired, the high frequency crystal can also be disabled
to save additional system power, however it does not contribute to the power from VBUS since it draws
power from the DVCC supply.

1.2.7.2 Entering Resume Mode

When the USB device is in a suspended condition, any non-idle signaling, including reset signaling, on the
host side is detected by the suspend and resume logic and device operation is resumed. RESRIFG is set,
causing an USB interrupt. The interrupt service routine can be used to resume USB operation.

1.3 USB Transfers

The USB module supports control, bulk, and interrupt data transfer types. In accordance with the USB
specification, endpoint 0 is reserved for the control endpoint and is bidirectional. In addition to the control
endpoint, the USB module is capable of supporting up to 7 input endpoints and 7 output endpoints. These
additional endpoints can be configured either as bulk or interrupt endpoints. The software handles all
control, bulk, and interrupt endpoint transactions.

1.3.1 Control Transfers

Control transfers are used for configuration, command, and status communication between the host and
the USB device. Control transfers to the USB device use input endpoint 0 and output endpoint 0. The
three types of control transfers are control write, control write with no data stage, and control read. Note
that the control endpoint must be initialized before connecting the USB device to the USB.

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1.3.1.1 Control Write Transfer

The host uses a control write transfer to write data to the USB device. A control write transfer consists of a
setup stage transaction, at least one output data stage transaction, and an input status stage transaction.
The stage transactions for a control write transfer are:
• Setup stage transaction:
1. Input endpoint 0 and output endpoint 0 are initialized by programming the appropriate USB
endpoint configuration blocks. This entails enabling the endpoint interrupt (USBIIE = 1) and
enabling the endpoint (UBME = 1). The NAK bit for both input endpoint 0 and output endpoint 0
must be cleared.
2. The host sends a setup token packet followed by the setup data packet addressed to output
endpoint 0. If the data is received without an error, then the UBM writes the data to the setup data
packet buffer, sets the setup stage transaction bit (SETUPIFG = 1) in the USB Interrupt Flag
register (USBIFG), returns an ACK handshake to the host, and asserts the setup stage transaction
interrupt. Note that as long as SETUPIFG = 1, the UBM returns a NAK handshake for any data
stage or status stage transactions regardless of the endpoint 0 NAK or STALL bit values.
3. The software services the interrupt, reads the setup data packet from the buffer, and then decodes
the command. If the command is not supported or invalid, the software should set the STALL bit in
the output endpoint 0 configuration register (USBOEPCNFG_0) and the input endpoint 0
configuration register (USBIEPCNFG_0) . This causes the device to return a STALL handshake for
any data or status stage transaction. For control write transfers, the packet ID used by the host for
the first data packet output is a DATA1 packet ID and the TOGGLE bit must match.

NOTE: When using USBIV, SETUPIFG is cleared upon reading USBIV. In addition, the NAK on
input endpoint 0 and output endpoint 0 are also cleared. In this case, the host may send or
receive the next setup packet even if MSP430 did not perform the first setup packet. To
prevent this, first read the SETUPIFG directly, perform the required setup, and then use the
USBIV for further processing.

NOTE: The priority of input endpoint 0 is higher than the setup flag inside USBIV (SETUPIFG).
Therefore, if both the USBIEPIFG.EP0 and SETUPIFG are pending, reading USBIV gives
the higher priority interrupt (EP0) as opposed to SETUPIFG. Therefore, read SETUPIFG
directly, process the pending setup packet, then proceed to read the USBIV.

• Data stage transaction:

1. The host sends an OUT token packet followed by a data packet addressed to output endpoint 0. If
the data is received without an error, the UBM writes the data to the output endpoint buffer
(USBOEP0BUF), updates the data count value, toggles the TOGGLE bit, sets the NAK bit, returns
an ACK handshake to the host , and asserts the output endpoint interrupt 0 (OEPIFG0).
2. The software services the interrupt and reads the data packet from the output endpoint buffer. To
read the data packet, the software first needs to obtain the data count value inside the
USBOEPBCNT_0 register. After reading the data packet, the software should clear the NAK bit to
allow the reception of the next data packet from the host.
3. If the NAK bit is set when the data packet is received, the UBM simply returns a NAK handshake to
the host. If the STALL bit is set when the data packet is received, the UBM simply returns a STALL
handshake to the host. If a CRC or bit stuff error occurs when the data packet is received, then no
handshake is returned to the host.
• Status stage transaction:
1. For input endpoint 0, the software updates the data count value to zero, sets the TOGGLE bit, then
clears the NAK bit to enable the data packet to be sent to the host. Note that for a status stage
transaction, a null data packet with a DATA1 packet ID is sent to the host.
2. The host sends an IN token packet addressed to input endpoint 0. After receiving the IN token, the
UBM transmits a null data packet to the host. If the data packet is received without errors by the
host, then an ACK handshake is returned. The UBM then toggles the TOGGLE bit and sets the
NAK bit.

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3. If the NAK bit is set when the IN token packet is received, the UBM simply returns a NAK
handshake to the host. If the STALL bit is set when the IN token packet is received, the UBM
simply returns a STALL handshake to the host. If no handshake packet is received from the host,
then the UBM prepares to retransmit the same data packet again.

1.3.1.2 Control Write Transfer with No Data Stage Transfer

The host uses a control write transfer to write data to the USB device. A control write with no data stage
transfer consists of a setup stage transaction and an input status stage transaction. For this type of
transfer, the data to be written to the USB device is contained in the two byte value field of the setup stage
transaction data packet.
The stage transactions for a control write transfer with no data stage transfer are:
• Setup stage transaction:
1. Input endpoint 0 and output endpoint 0 are initialized by programming the appropriate USB
endpoint configuration blocks. This entails programming the buffer size and buffer base address,
selecting the buffer mode, enabling the endpoint interrupt (USBIIE = 1), initializing the TOGGLE bit,
enabling the endpoint (UBME = 1). The NAK bit for both input endpoint 0 and output endpoint 0
must be cleared.
2. The host sends a setup token packet followed by the setup data packet addressed to output
endpoint 0. If the data is received without an error then the UBM writes the data to the setup data
packet buffer, sets the setup stage transaction (SETUP) bit in the USB status register, returns an
ACK handshake to the host, and asserts the setup stage transaction interrupt. Note that as long as
the setup transaction (SETUP) bit is set, the UBM returns a NAK handshake for any data stage or
status stage transaction regardless of the endpoint 0 NAK or STALL bit values.
3. The software services the interrupt and reads the setup data packet from the buffer then decodes
the command. If the command is not supported or invalid, the software should set the STALL bits in
the output endpoint 0 and the input endpoint 0 configuration registers before clearing the setup
stage transaction (SETUP) bit. This causes the device to return a STALL handshake for data or
status stage transactions. After reading the data packet and decoding the command, the software
should clear the interrupt, which automatically clears the setup stage transaction status bit.

NOTE: When using USBIV, the SETUPIFG is cleared upon reading USBIV. In addition, the NAK on
input endpoint 0 and output endpoint 0 is also cleared. In this case, the host may send or
receive the next setup packet even if MSP430 did not perform the first setup packet. To
prevent this, first read the SETUPIFG directly, perform the required setup, and then use the
USBIV for further processing.

NOTE: The priority of input endpoint 0 is higher than setup flag inside USBIV. Therefore, if both the
USBIEPIFG.EP0 and SETUPIFG are pending, reading the USBIV gives the higher priority
interrupt (EP0) as opposed to the SETUPIFG. Therefore, read SETUPIFG directly, process
the pending setup packet, then proceed to read the USBIV.

• Status stage transaction:

1. For input endpoint 0, the software updates the data count value to zero, sets the TOGGLE bit, then
clears the NAK bit to enable the data packet to be sent to the host. Note that for a status stage
transaction a null data packet with a DATA1 packet ID is sent to the host.
2. The host sends an IN token packet addressed to input endpoint 0. After receiving the IN token, the
UBM transmits a null data packet to the host. If the data packet is received without errors by the
host, then an ACK handshake is returned. The UBM then toggles the TOGGLE bit, sets the NAK
bit, and asserts the endpoint interrupt.
3. If the NAK bit is set when the IN token packet is received, the UBM simply returns a NAK
handshake to the host. If the STALL bit is set when the IN token packet is received, the UBM
simply returns a STALL handshake to the host. If no handshake packet is received from the host,
then the UBM prepares to retransmit the same data packet again.

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1.3.1.3 Control Read Transfer

The host uses a control read transfer to read data from the USB device. A control read transfer consists of
a setup stage transaction, at least one input data stage transaction and an output status stage transaction.
The stage transactions for a control read transfer are:
• Setup stage transaction:
1. Input endpoint 0 and output endpoint 0 are initialized by programming the appropriate USB
endpoint configuration blocks. This entails enabling the endpoint interrupt (USBIIE = 1) and
enabling the endpoint (UBME = 1). The NAK bit for both input endpoint 0 and output endpoint 0
must be cleared.
2. The host sends a setup token packet followed by the setup data packet addressed to output
endpoint 0. If the data is received without an error, then the UBM writes the data to the setup
buffer, sets the setup stage transaction (SETUP) bit in the USB status register, returns an ACK
handshake to the host, and asserts the setup stage transaction interrupt. Note that as long as the
setup transaction (SETUP) bit is set, the UBM returns a NAK handshake for any data stage or
status stage transactions regardless of the endpoint 0 NAK or STALL bit values.
3. The software services the interrupt and reads the setup data packet from the buffer then decodes
the command. If the command is not supported or invalid, the software should set the STALL bits in
the output endpoint 0 and the input endpoint 0 configuration registers before clearing the setup
stage transaction (SETUP) bit. This causes the device to return a STALL handshake for a data
stage or status stage transactions. After reading the data packet and decoding the command, the
software should clear the interrupt, which automatically clears the setup stage transaction status bit.
The software should also set the TOGGLE bit in the input endpoint 0 configuration register. For
control read transfers, the packet ID used by the host for the first input data packet is a DATA1
packet ID.

NOTE: When using USBIV, the SETUPIFG is cleared upon reading USBIV. In addition, it also the
clears NAK on input endpoint 0 and output endpoint 0. In this case, the host may send or
receive the next setup packet even if MSP430 did not perform the first setup packet. To
prevent this, first read the SETUPIFG directly, perform the required setup, and then use the
USBIV for further processing.

NOTE: The priority of input endpoint 0 is higher than the setup flag inside USBIV. Therefore, if both
the USBIEPIFG.EP0 and SETUPIFG are pending, reading the USBIV gives the higher
priority interrupt (EP0) as opposed to the SETUPIFG. Therefore, read SETUPIFG directly,
process the pending setup packet, then proceed to read the USBIV.

• Data stage transaction:

1. The data packet to be sent to the host is written to the input endpoint 0 buffer by the software. The
software also updates the data count value then clears the input endpoint 0 NAK bit to enable the
data packet to be sent to the host.
2. The host sends an IN token packet addressed to input endpoint 0. After receiving the IN token, the
UBM transmits the data packet to the host. If the data packet is received without errors by the host,
then an ACK handshake is returned. The UBM sets the NAK bit and asserts the endpoint interrupt.
3. The software services the interrupt and prepares to send the next data packet to the host.
4. If the NAK bit is set when the IN token packet is received, the UBM simply returns a NAK
handshake to the host. If the STALL bit is set when the IN token packet is received, the UBM
simply returns a STALL handshake to the host. If no handshake packet is received from the host,
then the UBM prepares to retransmit the same data packet again.
5. The software continues to send data packets until all data has been sent to the host.
• Status stage transaction:
1. For output endpoint 0, the software sets the TOGGLE bit, then clears the NAK bit to enable the
data packet to be sent to the host. Note that for a status stage transaction a null data packet with a
DATA1 packet ID is sent to the host.
2. The host sends an OUT token packet addressed to output endpoint 0. If the data packet is received
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without an error then the UBM updates the data count value, toggles the TOGGLE bit, sets the
NAK bit, returns an ACK handshake to the host, and asserts the endpoint interrupt.
3. The software services the interrupt. If the status stage transaction completed successfully, then the
software should clear the interrupt and clear the NAK bit.
4. If the NAK bit is set when the input data packet is received, the UBM simply returns a NAK
handshake to the host. If the STALL bit is set when the in data packet is received, the UBM simply
returns a STALL handshake to the host. If a CRC or bit stuff error occurs when the data packet is
received, then no handshake is returned to the host.

1.3.2 Interrupt Transfers

The USB module supports interrupt data transfers both to and from the host. Devices that need to send or
receive a small amount of data with a specified service period are best served by the interrupt transfer
type. Input endpoints 1 through 7 and output endpoints 1 through 7 can be configured as interrupt
endpoints.

1.3.2.1 Interrupt OUT Transfer

The steps for an interrupt OUT transfer are:
1. The software initializes one of the output endpoints as an output interrupt endpoint by programming the
appropriate endpoint configuration block. This entails programming the buffer size and buffer base
address, selecting the buffer mode, enabling the endpoint interrupt, initializing the toggle bit, enabling
the endpoint, and clearing the NAK bit.
2. The host sends an OUT token packet followed by a data packet addressed to the output endpoint. If
the data is received without an error then the UBM writes the data to the endpoint buffer, updates the
data count value, toggles the toggle bit, sets the NAK bit, returns an ACK handshake to the host, and
asserts the endpoint interrupt.
3. The software services the interrupt and reads the data packet from the buffer. To read the data packet,
the software first needs to obtain the data count value. After reading the data packet, the software
should clear the interrupt and clear the NAK bit to allow the reception of the next data packet from the
host.
4. If the NAK bit is set when the data packet is received, the UBM simply returns a NAK handshake to the
host. If the STALL bit is set when the data packet is received, the UBM simply returns a STALL
handshake to the host. If a CRC or bit stuff error occurs when the data packet is received, then no
handshake is returned to the host device.
In double buffer mode, the UBM selects between the X and Y buffer based on the value of the toggle bit. If
the toggle bit is a 0, the UBM writes the data packet to the X buffer. If the toggle bit is a 1, the UBM writes
the data packet to the Y buffer. When a data packet is received, the software could determine which buffer
contains the data packet by reading the toggle bit. However, when using double buffer mode, the
possibility exists for data packets to be received and written to both the X and Y buffer before the software
responds to the endpoint interrupt. In this case, simply using the toggle bit to determine which buffer
contains the data packet would not work. Hence, in double buffer mode, the software should read the X
buffer NAK bit, the Y buffer NAK bit, and the toggle bits to determine the status of the buffers.

1.3.2.2 Interrupt IN Transfer

The steps for an interrupt IN transfer are:
1. The software initializes one of the input endpoints as an input interrupt endpoint by programming the
appropriate endpoint configuration block. This entails programming the buffer size and buffer base
address, selecting the buffer mode, enabling the endpoint interrupt, initializing the toggle bit, enabling
the endpoint, and setting the NAK bit.
2. The data packet to be sent to the host is written to the buffer by the software. The software also
updates the data count value then clears the NAK bit to enable the data packet to be sent to the host.
3. The host sends an IN token packet addressed to the input endpoint. After receiving the IN token, the
UBM transmits the data packet to the host. If the data packet is received without errors by the host,
then an ACK handshake is returned. The UBM then toggles the toggle bit, sets the NAK bit, and
asserts the endpoint interrupt.

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4. The software services the interrupt and prepares to send the next data packet to the host.
5. If the NAK bit is set when the in token packet is received, the UBM simply returns a NAK handshake to
the host. If the STALL bit is set when the IN token packet is received, the UBM simply returns a STALL
handshake to the host. If no handshake packet is received from the host, then the UBM prepares to
retransmit the same data packet again.
In double buffer mode, the UBM selects between the X and Y buffer based on the value of the toggle bit. If
the toggle bit is a 0, the UBM reads the data packet from the X buffer. If the toggle bit is a 1, the UBM
reads the data packet from the Y buffer.

1.3.3 Bulk Transfers

The USB module supports bulk data transfers both to and from the host. Devices that need to send or
receive a large amount of data without a suitable bandwidth are best served by the bulk transfer type. In
endpoints 1 through 7 and out endpoints 1 through 7 can all be configured as bulk endpoints.

1.3.3.1 Bulk OUT Transfer

The steps for a bulk OUT transfer are:
1. The software initializes one of the output endpoints as an output bulk endpoint by programming the
appropriate endpoint configuration block. This entails programming the buffer size and buffer base
address, selecting the buffer mode, enabling the endpoint interrupt, initializing the toggle bit, enabling
the endpoint, and clearing the NAK bit.
2. The host sends an out token packet followed by a data packet addressed to the output endpoint. If the
data is received without an error then the UBM writes the data to the endpoint buffer, updates the data
count value, toggles the toggle bit, sets the NAK bit, returns an ACK handshake to the host, and
asserts the endpoint interrupt.
3. The software services the interrupt and reads the data packet from the buffer. To read the data packet,
the software first needs to obtain the data count value. After reading the data packet, the software
should clear the interrupt and clear the NAK bit to allow the reception of the next data packet from the
host.
4. If the NAK bit is set when the data packet is received, the UBM simply returns a NAK handshake to the
host. If the STALL bit is set when the data packet is received, the UBM simply returns a STALL
handshake to the host. If a CRC or bit stuff error occurs when the data packet is received, then no
handshake is returned to the host.
In double buffer mode, the UBM selects between the X and Y buffer based on the value of the toggle bit. If
the toggle bit is a 0, the UBM writes the data packet to the X buffer. If the toggle bit is a 1, the UBM writes
the data packet to the Y buffer. When a data packet is received, the software could determine which buffer
contains the data packet by reading the toggle bit. However, when using double buffer mode, the
possibility exists for data packets to be received and written to both the X and Y buffer before the software
responds to the endpoint interrupt. In this case, simply using the toggle bit to determine which buffer
contains the data packet would not work. Hence, in double buffer mode, the software should read the X
buffer NAK bit, the Y buffer NAK bit, and the toggle bits to determine the status of the buffers.

1.3.3.2 Bulk IN Transfer

The steps for a bulk IN transfer are:
1. The software initializes one of the input endpoints as an input bulk endpoint by programming the
appropriate endpoint configuration block. This entails programming the buffer size and buffer base
address, selecting the buffer mode, enabling the endpoint interrupt, initializing the toggle bit, enabling
the endpoint, and setting the NAK bit.
2. The data packet to be sent to the host is written to the buffer by the software. The software also
updates the data count value then clears the NAK bit to enable the data packet to be sent to the host.
3. The host sends an IN token packet addressed to the input endpoint. After receiving the IN token, the
UBM transmits the data packet to the host. If the data packet is received without errors by the host,
then an ACK handshake is returned. The UBM then toggles the toggle bit, sets the NAK bit, and
asserts the endpoint interrupt.

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4. The software services the interrupt and prepares to send the next data packet to the host.
5. If the NAK bit is set when the in token packet is received, the UBM simply returns a NAK handshake to
the host. If the STALL bit is set when the In token packet is received, the UBM simply returns a STALL
handshake to the host. If no handshake packet is received from the host, then the UBM prepares to
retransmit the same data packet again.
In double buffer mode , the UBM selects between the X and Y buffer based on the value of the toggle bit.
If the toggle bit is a 0, the UBM reads the data packet from the X buffer. If the toggle bit is a 1, the UBM
reads the data packet from the Y buffer.

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1.4 USB Registers

The USB register space is subdivided into configuration registers, control registers, and USB buffer
memory.
The configuration and control registers are physical registers located in peripheral memory, while the
buffer memory is implemented in RAM. See the device-specific data sheet for base addresses of these
register groupings.
The USB control registers can be written only while the USB module is enabled.
When the USB module is disabled, it no longer uses the RAM buffer memory. This memory then behaves
as a 2KB RAM block and can be used by the CPU or DMA without any limitation.

1.4.1 USB Configuration Registers

The configuration registers control the hardware functions needed to make a USB connection, including
the PHY, PLL, and LDOs.
Access to the configuration registers is allowed or disallowed using the USBKEYPID register. Writing the
proper value (9628h) unlocks the configuration registers and enables access. Writing any other value
disables access while leaving the values of the registers intact. Locking should be done intentionally after
the configuration is finished. Read access is available without the need to write to the USBKEYPID
register.
The configuration registers are listed in Table 1-5. All addresses are expressed as offsets; the base
address can be found in the device-specific data sheet.
All registers are byte and word accessible.

Table 1-5. USB Configuration Registers

Offset Acronym Register Name Type Reset Section
00h USBKEYPID USB controller key and ID register Read/Write 0000h Section 1.4.1.1
02h USBCNF USB controller configuration register Read/Write 0000h Section 1.4.1.2
04h USBPHYCTL USB-PHY control register Read/Write 0000h Section 1.4.1.3
08h USBPWRCTL USB-PWR control register Read/Write 1850h Section 1.4.1.4
10h USBPLLCTL USB-PLL control register Read/Write 0000h Section 1.4.1.5
12h USBPLLDIVB USB-PLL divider buffer register Read/Write 0000h Section 1.4.1.6
14h USBPLLIR USB-PLL interrupt register Read/Write 0000h Section 1.4.1.7

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1.4.1.1 USBKEYPID Register

USB Key Register

Figure 1-8. USBKEYPID Register

15 14 13 12 11 10 9 8
USBKEY
rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0
7 6 5 4 3 2 1 0
USBKEY
rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0

Table 1-6. USBKEYPID Register Description

Bit Field Type Reset Description
15-0 USBKEY RW 00h Key register. Must be written with a value of 9628h to be recognized as a valid
key. This "unlocks" the configuration registers. If written with any other value, the
registers become "locked". Reads back as A528h if the registers are unlocked.

1.4.1.2 USBCNF Register

USB Module Configuration Register
This register can be modified only when USBKEYPID is unlocked.

Figure 1-9. USBCNF Register

15 14 13 12 11 10 9 8
Reserved
r0 r0 r0 r0 r0 r0 r0 r0
7 6 5 4 3 2 1 0
Reserved FNTEN BLKRDY PUR_IN PUR_EN USB_EN
r0 r0 r0 rw-0 rw-0 r rw-0 rw-0
Can be modified only when USBKEYPID is unlocked.

Table 1-7. USBCNF Register Description

Bit Field Type Reset Description
15-5 Reserved R 0h Reserved. Always reads as 0.
4 FNTEN RW 0h Frame number receive trigger enable for DMA transfers
0b = Frame number receive trigger is blocked.
1b = Frame number receive trigger is gated through to DMA.
3 BLKRDY RW 0h Block transfer ready signaling for DMA transfers
0b = DMA triggering is disabled.
1b = DMA is triggered whenever the USB bus interface can accept new write
transfers.
2 PUR_IN R 0h PUR input value. This bit reflects the input value present on PUR. This bit may
be used as an indication to start a USB based boot loading program (USB-BSL).
The PUR input logic is powered by VUSB. PUR_IN returns zero when VUSB is
zero.
1 PUR_EN RW 0h PUR pin enable
0b = PUR pin is in high-impedance state
1b = PUR pin is driven high
0 USB_EN RW 0h USB module enable
0b = USB module is disabled
1b = USB module is enabled

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1.4.1.3 USBPHYCTL Register

USB-PHY Control Register
This register can be modified only when USBKEYPID is unlocked.

Figure 1-10. USBPHYCTL Register

15 14 13 12 11 10 9 8
Reserved Reserved PUIPE
r0 r0 r0 r0 r0 r0 rw-0 rw-0
7 6 5 4 3 2 1 0
PUSEL Reserved PUOPE Reserved PUIN1 PUIN0 PUOUT1 PUOUT0
rw-0 r rw-0 rw-0 r r rw-0 rw-0
Can be modified only when USBKEYPID is unlocked.

Table 1-8. USBPHYCTL Register Description

Bit Field Type Reset Description
15-10 Reserved R 0h Reserved. Always reads as 0.
9 Reserved RW 0h Reserved. Always write as 0.
8 PUIPE RW 0h PU input enable. This bit is valid only when PUSEL = 0.
0b = PU.0 and PU.1 inputs are disabled
1b = PU.0 and PU.1 inputs are enabled
7 PUSEL RW 0h USB port function select. This bit selects the function of the PU.0/DP and
PU.1/DM pins.
0b = PU.0 and PU.1 function selected (general purpose I/O)
1b = DP and DM function selected (USB terminals)
6 Reserved R 0h Reserved. Always reads as 0.
5 PUOPE RW 0h PU output enable. This bit is valid only when PUSEL = 0.
0b = PU.0 and PU.1 outputs are disabled
1b = PU.0 and PU.1 outputs are enabled.
4 Reserved RW 0h Reserved. Always write as 0.
3 PUIN1 R 0h PU.1 input data. This bit reflects the logic value on the PU.1 terminal when
PUIPE = 1.
2 PUIN0 R 0h PU.0 input data. This bit reflects the logic value on the PU.0 terminal when
PUIPE = 1.
1 PUOUT1 RW 0h PU.1 output data. This bits defines the value of the PU.1 pin when PUOPE = 1.
0 PUOUT0 RW 0h PU.0 output data. This bits defines the value of the PU.0 pin when PUOPE = 1.

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1.4.1.4 USBPWRCTL Register

USB-Power Control Register
This register can be modified only when USBKEYPID is unlocked.

Figure 1-11. USBPWRCTL Register

15 14 13 12 11 10 9 8
Reserved SLDOEN VUSBEN VBOFFIE VBONIE VUOVLIE
r0 r0 r0 rw-1 rw-1 rw-0 rw-0 rw-0
7 6 5 4 3 2 1 0
Reserved SLDOAON OVLAOFF USBDETEN USBBGVBV VBOFFIFG VBONIFG VUOVLIFG
r0 rw-1 rw-0 rw-1 r rw-0 rw-0 rw-0
Can be modified only when USBKEYPID is unlocked.

Table 1-9. USBPWRCTL Register Description

Bit Field Type Reset Description
15-13 Reserved R 0h Reserved. Always reads as 0.
12 SLDOEN RW 1h 1.8-V (secondary) LDO enable. When set, the LDO is enabled. Can be cleared
only if SLDOAON = 0.
0b = 1.8-V LDO is disabled
1b = 1.8-V LDO is enabled
11 VUSBEN RW 1h 3.3-V LDO enable. When set, the LDO is enabled.
0b = 3.3-V LDO is disabled
1b = 3.3-V LDO is enabled
10 VBOFFIE RW 0h VBUS "going OFF" interrupt enable
0b = Interrupt disabled
1b = Interrupt enabled
9 VBONIE RW 0h VBUS "coming ON" interrupt enable
0b = Interrupt disabled
1b = Interrupt enabled
8 VUOVLIE RW 0h VUSB overload indication interrupt enable
0b = Interrupt disabled
1b = Interrupt enabled
7 Reserved R 0h Reserved. Always reads as 0.
6 SLDOAON RW 1h 1.8-V LDO auto-on enable
0b = LDO must be turned on manually using SLDOEN
1b = A "VBUS coming on" enables the secondary LDO, but SLDOEN is not set
automatically.
5 OVLAOFF RW 0h LDO overload auto-off enable
0b = During an overload on the 3.3-V LDO, the LDO automatically enters
current-limiting mode and stays there until the condition stops.
1b = An overload indication clears the VUSBEN bit.
4 USBDETEN RW 1h Enable bit for VBUS on and off events.
0b = USB module does not detect USB-PWR VBUS on and off events
1b = USB module does detect USB-PWR VBUS on and off events
3 USBBGVBV R 0h VBUS valid
0b = VBUS is not valid yet
1b = VBUS is valid and within bounds

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Table 1-9. USBPWRCTL Register Description (continued)

Bit Field Type Reset Description
2 VBOFFIFG RW 0h VBUS "going OFF" interrupt flag. This bit indicates that VBUS fell below the
launch voltage. It is automatically cleared when the corresponding vector of the
USB interrupt vector register is read, or if a value is written to the interrupt vector
register.
0b = VBUS did not fall below the launch voltage.
1b = VBUS fell below the launch voltage.
1 VBONIFG RW 0h VBUS "coming ON" interrupt flag. This bit indicates that VBUS rose above the
launch voltage. This bit is automatically cleared when the corresponding vector
of the USB interrupt vector register is read, or if a value is written to the interrupt
vector register.
0b = VUSB did not rise above the launch voltage.
1b = VUSB rose above the launch voltage.
0 VUOVLIFG RW 0h VUSB overload interrupt flag. This bit indicates that the 3.3-V LDO entered an
overload condition.
0b = No overload condition detected.
1b = Overload condition detected.

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1.4.1.5 USBPLLCTL Register

USB-PLL Control Register
This register can be modified only when USBKEYPID is unlocked.

Figure 1-12. USBPLLCTL Register

15 14 13 12 11 10 9 8
Reserved UPFDEN UPLLEN
r0 r0 r0 r-0 r0 r0 rw-0 rw-0
7 6 5 4 3 2 1 0
UCLKSEL Reserved
rw-0 rw-0 r0 r0 r0 r0 r0 r0
Can be modified only when USBKEYPID is unlocked.

Table 1-10. USBPLLCTL Register Description

Bit Field Type Reset Description
15-10 Reserved R 0h Reserved. Always reads as 0.
9 UPFDEN RW 0h Phase frequency discriminator (PFD) enable
0b = PFD is disabled
1b = PFD is enabled
8 UPLLEN RW 0h PLL enable
0b = PLL is disabled
1b = PLL is enabled
7-6 UCLKSEL RW 0h USB module clock select. Must always be written with 00.
00b = PLLCLK (default)
01b = Reserved
10b = Reserved
11b = Reserved
5-0 Reserved R 0h Reserved. Always reads as 0.

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1.4.1.6 USBPLLDIVB Register

USB-PLL Clock Divider Buffer Register
This register can be modified only when USBKEYPID is unlocked.

Figure 1-13. USBPLLDIVB Register

15 14 13 12 11 10 9 8
Reserved UPQB
r0 r0 r0 r0 r0 rw-0 rw-0 rw-0
7 6 5 4 3 2 1 0
Reserved UPMB
r0 r0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0
Can be modified only when USBKEYPID is unlocked.

Table 1-11. USBPLLDIVB Register Description

Bit Field Type Reset Description
15-11 Reserved R 0h Reserved. Always reads as 0.
10-8 UPQB RW 0h PLL pre-scale divider buffer register. These bits select the pre-scale division
value. The value of this register is transferred to UPQB as soon it is written.
000b = fUPD = fREF
001b = fUPD = fREF / 2
010b = fUPD = fREF / 3
011b = fUPD = fREF / 4
100b = fUPD = fREF / 6
101b = fUPD = fREF / 8
110b = fUPD = fREF / 13
111b = fUPD = fREF / 16
7-6 Reserved R 0h Reserved. Always reads as 0.
5-0 UPMB RW 0h USB PLL feedback divider buffer register. These bits select the value of the
feedback divider. The value of this register is transferred to UPMB automatically
when UPQB is written.
000000b = Feedback division rate: 1
000001b = Feedback division rate: 2
⋮
111111b = Feedback division rate: 64

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1.4.1.7 USBPLLIR Register

USB-PLL Interrupt Register
This register can be modified only when USBKEYPID is unlocked.

Figure 1-14. USBPLLIR Register

15 14 13 12 11 10 9 8
Reserved USBOORIE USBLOSIE USBOOLIE
r0 r0 r0 r0 r0 rw-0 rw-0 rw-0
7 6 5 4 3 2 1 0
Reserved USBOORIFG USBLOSIFG USBOOLIFG
r0 r0 r0 r0 r0 rw-0 rw-0 rw-0
Can be modified only when USBKEYPID is unlocked.

Table 1-12. USBPLLIR Register Description

Bit Field Type Reset Description
15-11 Reserved R 0h Reserved. Always reads as 0.
10 USBOORIE RW 0h PLL out-of-range interrupt enable
0b = Interrupt disabled
1b = Interrupt enabled
9 USBLOSIE RW 0h PLL loss-of-signal interrupt enable
0b = Interrupt disabled
1b = Interrupt enabled
8 USBOOLIE RW 0h PLL out-of-lock interrupt enable
0b = Interrupt disabled
1b = Interrupt enabled
7-3 Reserved R 0h Reserved. Always reads as 0.
2 USBOORIFG RW 0h PLL out-of-range interrupt flag
0b = No interrupt pending
1b = Interrupt pending
1 USBLOSIFG RW 0h PLL loss-of-signal interrupt flag
0b = No interrupt pending
1b = Interrupt pending
0 USBOOLIFG RW 0h PLL out-of-lock interrupt flag
0b = No interrupt pending
1b = Interrupt pending

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1.4.2 USB Control Registers

The control registers affect core USB operations that are fundamental for any USB connection. This
includes control endpoint 0, interrupts, bus address and frame, and timestamps. Control of endpoints other
than zero are found in the operation registers. Unlike the operation registers, the control registers are
actual physical registers, whereas the operation registers exist in RAM, which can be re-allocated to
general-purpose use.
The control registers are listed in Table 1-13. All addresses are expressed as offsets; the base address
can be found in the device-specific data sheet.
All registers are byte and word accessible.

Table 1-13. USB Control Registers

Offset Acronym Register Name Type Reset Section
00h USBIEPCNF_0 Input endpoint_0: Configuration Read/Write 00h Section 1.4.2.1
01h USBIEPBCNT_0 Input endpoint_0: Byte Count Read/Write 80h Section 1.4.2.2
02h USBOEPCNFG_0 Output endpoint_0: Configuration Read/Write 00h Section 1.4.2.3
03h USBOEPBCNT_0 Output endpoint_0: Byte count Read/Write 00h Section 1.4.2.4
0Eh USBIEPIE Input endpoint interrupt enables Read/Write 00h Section 1.4.2.5
0Fh USBOEPIE Output endpoint interrupt enables Read/Write 00h Section 1.4.2.6
10h USBIEPIFG Input endpoint interrupt flags Read/Write 00h Section 1.4.2.7
11h USBOEPIFG Output endpoint interrupt flags Read/Write 00h Section 1.4.2.8
12h USBVECINT Vector interrupt register Read/Write 0000h Section 1.4.2.9
or USBIV
16h USBMAINT Timestamp maintenance register Read/Write 0000h Section 1.4.2.10
18h USBTSREG Timestamp register Read/Write 0000h Section 1.4.2.11
1Ah USBFN USB frame number Read only 0000h Section 1.4.2.12
1Ch USBCTL USB control register Read/Write 00h Section 1.4.2.13
1Dh USBIE USB interrupt enable register Read/Write 00h Section 1.4.2.14
1Eh USBIFG USB interrupt flag register Read/Write 00h Section 1.4.2.15
1Fh USBFUNADR Function address register Read/Write 00h Section 1.4.2.16

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1.4.2.1 USBIEPCNF_0 Register

USB Input Endpoint-0 Configuration Register

Figure 1-15. USBIEPCNF_0 Register

7 6 5 4 3 2 1 0
UBME Reserved TOGGLE Reserved STALL USBIIE Reserved
rw-0 r0 r-0 r0 rw-0 rw-0 r0 r0
Can be modified only when USBEN = 1.

Table 1-14. USBIEPCNF_0 Register Description

Bit Field Type Reset Description
7 UBME RW 0h UBM in endpoint-0 enable
0b = UBM cannot use this endpoint
1b = UBM can use this endpoint
6 Reserved R 0h Reserved. Always reads as 0.
5 TOGGLE R 0h Toggle bit. Reads as 0, because the configuration endpoint does not need to
toggle.
4 Reserved R 0h Reserved. Always reads as 0.
3 STALL RW 0h USB stall condition. When set, hardware automatically returns a stall handshake
to the USB host for any transaction transmitted from endpoint-0. The stall bit is
cleared automatically by the next setup transaction.
0b = Indicates no stall
1b = Indicates stall
2 USBIIE RW 0h USB transaction interrupt indication enable. Software may set this bit to define if
interrupts are to be flagged in general. To generate an interrupt the
corresponding interrupt flag must be set (IEPIE).
0b = Corresponding interrupt flag is not set
1b = Corresponding interrupt flag is set
1-0 Reserved R 0h Reserved. Always reads as 0.

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1.4.2.2 USBIEPBCNT_0 Register

USB Input Endpoint-0 Byte Count Register

Figure 1-16. USBIEPBCNT_0 Register

7 6 5 4 3 2 1 0
NAK Reserved CNT
rw-0 r0 r0 r0 rw-0 rw-0 rw-0 rw-0
Can be modified only when USBEN = 1

Table 1-15. USBIEPBCNT_0 Register Description

Bit Field Type Reset Description
7 NAK RW 0h No acknowledge status bit. This bit is set by the UBM at the end of a successful
USB IN transaction from endpoint-0, to indicate that the EP-0 IN buffer is empty.
When this bit is set, all subsequent transactions from endpoint-0 result in a NAK
handshake response to the USB host. To re-enable this endpoint to transmit
another data packet to the host, this bit must be cleared by software.
0b = Buffer contains a valid data packet for host device
1b = Buffer is empty (Host-In request receives a NAK)
6-4 Reserved R 0h Reserved. Always reads as 0.
3-0 CNT RW 0h Byte count. The In_EP-0 buffer data count value should be set by software when
a new data packet is written to the buffer. This four-bit value contains the number
of bytes in the data packet.
0000b to 1000b are valid numbers for 0 to 8 bytes to be sent.
1001b to 1111b are reserved values (if used, defaults to 8).

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1.4.2.3 USBOEPCNFG_0 Register

USB Output Endpoint-0 Configuration Register

Figure 1-17. USBOEPCNFG_0 Register

7 6 5 4 3 2 1 0
UBME Reserved TOGGLE Reserved STALL USBIIE Reserved
rw-0 r0 r-0 r0 rw-0 rw-0 r0 r0
Can be modified only when USBEN = 1

Table 1-16. USBOEPCNFG_0 Register Description

Bit Field Type Reset Description
7 UBME RW 0h UBM out Endpoint-0 enable
0b = UBM cannot use this endpoint
1b = UBM can use this endpoint
6 Reserved R 0h Reserved. Always reads as 0.
5 TOGGLE RW 0h Toggle bit. Reads as 0, because the configuration endpoint does not need to
toggle.
4 Reserved R 0h Reserved. Always reads as 0.
3 STALL RW 0h USB stall condition. When set, hardware automatically returns a stall handshake
to the USB host for any transaction transmitted into endpoint-0. The stall bit is
cleared automatically by the next setup transaction.
0b = Indicates no stall
1b = Indicates stall
2 USBIIE RW 0h USB transaction interrupt indication enable. Software may set this bit to define if
interrupts are to be flagged in general. To generate an interrupt the
corresponding interrupt flag must be set (OEPIE).
0b = Corresponding interrupt flag will not be set
1b = Corresponding interrupt flag will be set
1-0 Reserved R 0h Reserved. Always reads as 0.

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1.4.2.4 USBOEPBCNT_0 Register

USB Output Endpoint-0 Byte Count Register

Figure 1-18. USBOEPBCNT_0 Register

7 6 5 4 3 2 1 0
NAK Reserved CNT
rw-0 r0 r0 r0 rw-0 rw-0 rw-0 rw-0
Can be modified only when USBEN = 1

Table 1-17. USBOEPBCNT_0 Register Description

Bit Field Type Reset Description
7 NAK RW 0h No acknowledge status bit. This bit is set by the UBM at the end of a successful
USB out transaction into endpoint-0, to indicate that the EP-0 buffer contains a
valid data packet and that the buffer data count value is valid. When this bit is
set, all subsequent transactions to endpoint-0 result in a NAK handshake
response to the USB host. To re-enable this endpoint to receive another data
packet from the host, this bit must be cleared by software.
0b = No valid data in the buffer. The buffer is ready to receive a host OUT
transaction
1b = The buffer contains a valid packet from the host that has not been picked
up. (Any subsequent Host-Out requests receive a NAK.)
6-4 Reserved R 0h Reserved. Always reads as 0.
3-0 CNT RW 0h Byte count. This data count value is set by the UBM when a new data packet is
received by the buffer for the out endpoint-0. The four-bit value contains the
number of bytes received in the data buffer.
0000b to 1000b are valid numbers for 0 to 8 received bytes
1001b to 1111b are reserved values

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1.4.2.5 USBIEPIE Register

USB Input Endpoint Interrupt Enable Register

Figure 1-19. USBIEPIE Register

7 6 5 4 3 2 1 0
IEPIE7 IEPIE6 IEPIE5 IEPIE4 IEPIE3 IEPIE2 IEPIE1 IEPIE0
rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0
Can be modified only when USBEN = 1

Table 1-18. USBIEPIE Register Description

Bit Field Type Reset Description
7 IEPIE7 RW 0h Input endpoint interrupt enable 7. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
6 IEPIE6 RW 0h Input endpoint interrupt enable 6. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
5 IEPIE5 RW 0h Input endpoint interrupt enable 5. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
4 IEPIE4 RW 0h Input endpoint interrupt enable 4. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
3 IEPIE3 RW 0h Input endpoint interrupt enable 3. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
2 IEPIE2 RW 0h Input endpoint interrupt enable 2. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
1 IEPIE1 RW 0h Input endpoint interrupt enable 1. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt

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Table 1-18. USBIEPIE Register Description (continued)

Bit Field Type Reset Description
0 IEPIE0 RW 0h Input endpoint interrupt enable 0. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt

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1.4.2.6 USBOEPIE Register

USB Output Endpoint Interrupt Enable Register

Figure 1-20. USBOEPIE Register

7 6 5 4 3 2 1 0
OEPIE7 OEPIE6 OEPIE5 OEPIE4 OEPIE3 OEPIE2 OEPIE1 OEPIE0
rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0
Can be modified only when USBEN = 1

Table 1-19. USBOEPIE Register Description

Bit Field Type Reset Description
7 OEPIE7 RW 0h Output endpoint interrupt enable 7. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
6 OEPIE6 RW 0h Output endpoint interrupt enable 6. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
5 OEPIE5 RW 0h Output endpoint interrupt enable 5. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
4 OEPIE4 RW 0h Output endpoint interrupt enable 4. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
3 OEPIE3 RW 0h Output endpoint interrupt enable 3. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
2 OEPIE2 RW 0h Output endpoint interrupt enable 2. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt
1 OEPIE1 RW 0h Output endpoint interrupt enable 1. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt

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Table 1-19. USBOEPIE Register Description (continued)

Bit Field Type Reset Description
0 OEPIE0 RW 0h Output endpoint interrupt enable 0. This bit enables or disables whether an event
can trigger an interrupt. It does not influence whether the event is flagged; the
flag is enabled or disabled with the interrupt indication enable bit in the Endpoint
descriptors.
0b = Event does not generate an interrupt
1b = Event does generate an interrupt

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1.4.2.7 USBIEPIFG Register

USB Input Endpoint Interrupt Flag Register

Figure 1-21. USBIEPIFG Register

7 6 5 4 3 2 1 0
IEPIFG7 IEPIFG6 IEPIFG5 IEPIFG4 IEPIFG3 IEPIFG2 IEPIFG1 IEPIFG0
rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0
Can be modified only when USBEN = 1

Table 1-20. USBIEPIFG Register Description

Bit Field Type Reset Description
7 IEPIFG7 RW 0h Input endpoint interrupt flag 7. This bit is set by the UBM when a successful
completion of a transaction occurs for this endpoint. When set, a USB interrupt is
generated. The interrupt flag is cleared when the MCU reads the value from the
USBVECINT (USBIV) register corresponding with this interrupt, or when it writes
any value to the interrupt vector register. An interrupt flag can also be cleared by
writing zero to that bit location.
6 IEPIFG6 RW 0h Input endpoint interrupt flag 6. This bit is set by the UBM when a successful
completion of a transaction occurs for this endpoint. When set, a USB interrupt is
generated. The interrupt flag is cleared when the MCU reads the value from the
USBVECINT (USBIV) register corresponding with this interrupt, or when it writes
any value to the interrupt vector register. An interrupt flag can also be cleared by
writing zero to that bit location.
5 IEPIFG5 RW 0h Input endpoint interrupt flag 5. This bit is set by the UBM when a successful
completion of a transaction occurs for this endpoint. When set, a USB interrupt is
generated. The interrupt flag is cleared when the MCU reads the value from the
USBVECINT (USBIV) register corresponding with this interrupt, or when it writes
any value to the interrupt vector register. An interrupt flag can also be cleared by
writing zero to that bit location.
4 IEPIFG4 RW 0h Input endpoint interrupt flag 4. This bit is set by the UBM when a successful
completion of a transaction occurs for this endpoint. When set, a USB interrupt is
generated. The interrupt flag is cleared when the MCU reads the value from the
USBVECINT (USBIV) register corresponding with this interrupt, or when it writes
any value to the interrupt vector register. An interrupt flag can also be cleared by
writing zero to that bit location.
3 IEPIFG3 RW 0h Input endpoint interrupt flag 3. This bit is set by the UBM when a successful
completion of a transaction occurs for this endpoint. When set, a USB interrupt is
generated. The interrupt flag is cleared when the MCU reads the value from the
USBVECINT (USBIV) register corresponding with this interrupt, or when it writes
any value to the interrupt vector register. An interrupt flag can also be cleared by
writing zero to that bit location.
2 IEPIFG2 RW 0h Input endpoint interrupt flag 2. This bit is set by the UBM when a successful
completion of a transaction occurs for this endpoint. When set, a USB interrupt is
generated. The interrupt flag is cleared when the MCU reads the value from the
USBVECINT (USBIV) register corresponding with this interrupt, or when it writes
any value to the interrupt vector register. An interrupt flag can also be cleared by
writing zero to that bit location.
1 IEPIFG1 RW 0h Input endpoint interrupt flag 1. This bit is set by the UBM when a successful
completion of a transaction occurs for this endpoint. When set, a USB interrupt is
generated. The interrupt flag is cleared when the MCU reads the value from the
USBVECINT (USBIV) register corresponding with this interrupt, or when it writes
any value to the interrupt vector register. An interrupt flag can also be cleared by
writing zero to that bit location.
0 IEPIFG0 RW 0h Input endpoint interrupt flag 0. This bit is set by the UBM when a successful
completion of a transaction occurs for this endpoint. When set, a USB interrupt is
generated. The interrupt flag is cleared when the MCU reads the value from the
USBVECINT (USBIV) register corresponding with this interrupt, or when it writes
any value to the interrupt vector register. An interrupt flag can also be cleared by
writing zero to that bit location.

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1.4.2.8 USBOEPIFG Register

USB Output Endpoint Interrupt Flag Register

Figure 1-22. USBOEPIFG Register

7 6 5 4 3 2 1 0
OEPIFG7 OEPIFG6 OEPIFG5 OEPIFG4 OEPIFG3 OEPIFG2 OEPIFG1 OEPIFG0
rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0
Can be modified only when USBEN = 1

Table 1-21. USBOEPIFG Register Description

Bit Field Type Reset Description
7 OEPIFG7 RW 0h Output endpoint interrupt flag 7. The output endpoint interrupt flag is set to 1 by
the UBM when a successful completion of a transaction occurs to that out
endpoint. When the bit is set, a USB interrupt is generated. The interrupt flag is
cleared when the MCU reads the value from the USBVECINT (USBIV) register
corresponding with this interrupt, or when it writes any value to the interrupt
vector register. An interrupt flag can also be cleared by writing a zero to this bit
location.
6 OEPIFG6 RW 0h Output endpoint interrupt flag 6. The output endpoint interrupt flag is set to 1 by
the UBM when a successful completion of a transaction occurs to that out
endpoint. When the bit is set, a USB interrupt is generated. The interrupt flag is
cleared when the MCU reads the value from the USBVECINT (USBIV) register
corresponding with this interrupt, or when it writes any value to the interrupt
vector register. An interrupt flag can also be cleared by writing a zero to this bit
location.
5 OEPIFG5 RW 0h Output endpoint interrupt flag 5. The output endpoint interrupt flag is set to 1 by
the UBM when a successful completion of a transaction occurs to that out
endpoint. When the bit is set, a USB interrupt is generated. The interrupt flag is
cleared when the MCU reads the value from the USBVECINT (USBIV) register
corresponding with this interrupt, or when it writes any value to the interrupt
vector register. An interrupt flag can also be cleared by writing a zero to this bit
location.
4 OEPIFG4 RW 0h Output endpoint interrupt flag 4. The output endpoint interrupt flag is set to 1 by
the UBM when a successful completion of a transaction occurs to that out
endpoint. When the bit is set, a USB interrupt is generated. The interrupt flag is
cleared when the MCU reads the value from the USBVECINT (USBIV) register
corresponding with this interrupt, or when it writes any value to the interrupt
vector register. An interrupt flag can also be cleared by writing a zero to this bit
location.
3 OEPIFG3 RW 0h Output endpoint interrupt flag 3. The output endpoint interrupt flag set to 1 by the
UBM when a successful completion of a transaction occurs to that out endpoint.
When the bit is set, a USB interrupt is generated. The interrupt flag is cleared
when the MCU reads the value from the USBVECINT (USBIV) register
corresponding with this interrupt, or when it writes any value to the interrupt
vector register. An interrupt flag can also be cleared by writing a zero to this bit
location.
2 OEPIFG2 RW 0h Output endpoint interrupt flag 2. The output endpoint interrupt flag set to 1 by the
UBM when a successful completion of a transaction occurs to that out endpoint.
When the bit is set, a USB interrupt is generated. The interrupt flag is cleared
when the MCU reads the value from the USBVECINT (USBIV) register
corresponding with this interrupt, or when it writes any value to the interrupt
vector register. An interrupt flag can also be cleared by writing a zero to this bit
location.
1 OEPIFG1 RW 0h Output endpoint interrupt flag 1. The output endpoint interrupt flag set to 1 by the
UBM when a successful completion of a transaction occurs to that out endpoint.
When the bit is set, a USB interrupt is generated. The interrupt flag is cleared
when the MCU reads the value from the USBVECINT (USBIV) register
corresponding with this interrupt, or when it writes any value to the interrupt
vector register. An interrupt flag can also be cleared by writing a zero to this bit
location.

40 USB Module SLAU284F – August 2012 – Revised March 2018

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Table 1-21. USBOEPIFG Register Description (continued)

Bit Field Type Reset Description
0 OEPIFG0 RW 0h Output endpoint interrupt flag 0. The output endpoint interrupt flag set to 1 by the
UBM when a successful completion of a transaction occurs to that out endpoint.
When the bit is set, a USB interrupt is generated. The interrupt flag is cleared
when the MCU reads the value from the USBVECINT (USBIV) register
corresponding with this interrupt, or when it writes any value to the interrupt
vector register. An interrupt flag can also be cleared by writing a zero to this bit
location.

1.4.2.9 USBVECINT Register

USB Interrupt Vector Register
This register is also referred to as USBIV.

Figure 1-23. USBVECINT Register

15 14 13 12 11 10 9 8
USBIV
r0 r0 r0 r0 r0 r0 r0 r0
7 6 5 4 3 2 1 0
USBIV
r0 r0 r-0 r-0 r-0 r-0 r-0 r0

Table 1-22. USBVECINT Register Description

Bit Field Type Reset Description
15-0 USBIV R 0h USB interrupt vector value. This register is to be accessed as a whole word only.
When an interrupt is pending, reading this register results in a value that can be
added to the program counter to handle the corresponding event. Writing to this
register clears all pending USB interrupt flags independent of the status of
USBEN.
00h = No interrupt pending
02h = See Section 1.2.5.; Interrupt Priority: Highest
3Eh = Interrupt Priority: Lowest

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1.4.2.10 USBMAINT Register

Timestamp Maintenance Register

Figure 1-24. USBMAINT Register

15 14 13 12 11 10 9 8
UTSEL Reserved TSE3 TSESEL TSGEN
rw-0 rw-0 rw-0 r0 rw-0 rw-0 rw-0 rw-0
7 6 5 4 3 2 1 0
Reserved UTIE UTIFG
r0 r0 r0 r0 r0 r0 rw-0 rw-0
Can be modified only when USBEN = 1

Table 1-23. USBMAINT Register Description

Bit Field Type Reset Description
15-13 UTSEL RW 0h USB timer selection
000b = USB Timer Period: 4096 µs; Approximate Frequency: 250 Hz (244 Hz)
001b = USB Timer Period: 2048 µs; Approximate Frequency: 500 Hz (488 Hz)
010b = USB Timer Period: 1024 µs; Approximate Frequency: 1 kHz (977 Hz)
011b = USB Timer Period: 512 µs; Approximate Frequency: 2 kHz (1953 Hz)
100b = USB Timer Period: 256 µs; Approximate Frequency: 4 kHz (3906 Hz)
101b = USB Timer Period: 128 µs; Approximate Frequency: 8 kHz (7812 Hz)
110b = USB Timer Period: 64 µs; Approximate Frequency: 16 kHz (15625 Hz)
111b = USB Timer Period: 32 µs; Approximate Frequency: 31 kHz (31250 Hz)
12 Reserved R 0h Reserved. Always reads as 0.
11 TSE3 RW 0h Timestamp Event 3 bit. This bit allows the triggering of a software-driven
timestamp event (when TSESEL = 11b).
0b = No TSE3 event signaled
1b = TSE3 event signaled
10-9 TSESEL RW 0h Timestamp Event Selection. TSE[2:0] are connected to the event multiplexer of
the three DMA channels of the DMA controller if not otherwise noted in data
sheet
00b = TSE0 (DMA0) signal is qualified timestamp event
01b = TSE1 (DMA1) signal is qualified timestamp event
10b = TSE2 (DMA2) signal is qualified timestamp event
11b = Software-driven timestamp event
8 TSGEN RW 0h Timestamp generator enable
0b = Timestamp mechanism disabled
1b = Timestamp mechanism enabled
7-2 Reserved R 0h Reserved. Always reads as 0.
1 UTIE RW 0h USB timer interrupt enable bit
0b = USB timer interrupt disabled
1b = USB timer interrupt enabled
0 UTIFG RW 0h USB timer interrupt flag
0b = No interrupt pending
1b = Interrupt pending

42 USB Module SLAU284F – August 2012 – Revised March 2018

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1.4.2.11 USBTSREG Register

USB Timestamp Register

Figure 1-25. USBTSREG Register

15 14 13 12 11 10 9 8
TVAL
r-0 r-0 r-0 r-0 r-0 r-0 r-0 r-0
7 6 5 4 3 2 1 0
TVAL
r-0 r-0 r-0 r-0 r-0 r-0 r-0 r-0
Can be modified only when USBEN = 1

Table 1-24. USBTSREG Register Description

Bit Field Type Reset Description
15-0 TVAL R 0h Timestamp high register. The timestamp value is updated by hardware from the
USB timer. A qualified timestamp trigger signal causes the current timer value to
be latched into this register.

1.4.2.12 USBFN Register

USB Frame Number Register

Figure 1-26. USBFN Register

15 14 13 12 11 10 9 8
Reserved USBFN
r0 r0 r0 r0 r0 r-0 r-0 r-0
7 6 5 4 3 2 1 0
USBFN
r-0 r-0 r-0 r-0 r-0 r-0 r-0 r-0

Table 1-25. USBFN Register Description

Bit Field Type Reset Description
15-11 Reserved R 0h Reserved. Always reads as 0.
10-0 USBFN R 0h USB Frame Number register. The frame number bit values are updated by
hardware; each USB frame with the frame number field value received in the
USB start-of-frame packet. The frame number can be used as a timestamp. If
the local (MSP430's) frame timer is not locked to the USB host's frame timer,
then the frame number is automatically incremented from the previous value
when a pseudo start-of-frame occurs.

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1.4.2.13 USBCTL Register

USB Control Register

Figure 1-27. USBCTL Register

7 6 5 4 3 2 1 0
Reserved FEN RWUP FRSTE Reserved DIR
r0 rw-0 rw-0 rw-0 r0 r0 r0 rw-0
Can be modified only when USBEN = 1

Table 1-26. USBCTL Register Description

Bit Field Type Reset Description
7 Reserved R 0h Reserved. Always reads as 0.
6 FEN RW 0h Function Enable Bit. This bit needs to be set to enable the USB device to
respond to USB transactions. If this bit is not set, the UBM ignores all USB
transactions. It is cleared by a USB reset. (This bit is primarily intended for
debugging.)
0b = Function is disabled
1b = Function is enabled
5 RWUP RW 0h Device Remote Wakeup request. The remote wake-up bit is set by software to
request the suspend/resume logic to generate resume signaling upstream on the
USB. This bit is used to exit a USB low-power suspend state when a remote
wake-up event occurs. The bit is self-clearing.
0b = Writing 0 has no effect
1b = A Remote-Wakeup pulse is generated
4 FRSTE RW 0h Function Reset Connection Enable. This bit selects whether a bus reset on the
USB causes an internal reset of the USB module.
0b = Bus reset does not cause a reset of the module
1b = Bus reset does cause a reset of the module
3-1 Reserved R 0h Reserved. Always reads as 0.
0 DIR RW 0h Data response to setup packet interrupt status bit. Software must decode the
request and set/clear this bit to reflect the data transfer direction.
0b = USB data-OUT transaction (from host to device)
1b = USB data-IN transaction (from device to host)

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1.4.2.14 USBIE Register

USB Interrupt Enable Register

Figure 1-28. USBIE Register

7 6 5 4 3 2 1 0
RSTRIE SUSRIE RESRIE Reserved SETUPIE Reserved STPOWIE
rw-0 rw-0 rw-0 r0 r0 rw-0 r0 rw-0
Can be modified only when USBEN = 1

Table 1-27. USBIE Register Description

Bit Field Type Reset Description
7 RSTRIE RW 0h USB reset interrupt enable. Causes an interrupt to be generated if the RSTRIFG
bit is set.
0b = Function Reset interrupt disabled
1b = Function Reset interrupt enabled
6 SUSRIE RW 0h Suspend interrupt enable. Causes an interrupt to be generated if the SUSRIFG
bit is set.
0b = Suspend interrupt disabled
1b = Suspend interrupt enabled
5 RESRIE RW 0h Resume interrupt enable. Causes an interrupt to be generated if the RESRIFG
bit is set.
0b = Resume interrupt disabled
1b = Resume interrupt enabled
4-3 Reserved R 0h Reserved. Always reads as 0.
2 SETUPIE RW 0h Setup interrupt enable. Causes an interrupt to be generated if the SETUPIFG bit
is set.
0b = Setup interrupt disabled
1b = Setup interrupt enabled
1 Reserved R 0h Reserved. Always reads as 0.
0 STPOWIE RW 0h Setup Overwrite interrupt enable. Causes an interrupt to be generated if the
STPOWIFG bit is set.
0b = Setup Overwrite interrupt disabled
1b = Setup Overwrite interrupt enabled

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1.4.2.15 USBIFG Register

USB Interrupt Flag Register

Figure 1-29. USBIFG Register

7 6 5 4 3 2 1 0
RSTRIFG SUSRIFG RESRIFG Reserved SETUPIFG Reserved STPOWIFG
rw-0 rw-0 rw-0 r0 r0 rw-0 r0 rw-0
Can be modified only when USBEN = 1

Table 1-28. USBIFG Register Description

Bit Field Type Reset Description
7 RSTRIFG RW 0h USB reset request bit. This bit is set to one by hardware in response to the host
initiating a USB port reset. A USB reset causes a reset of the USB module logic,
but this bit is not affected.
6 SUSRIFG RW 0h Suspend request bit. This bit is set by hardware in response to the host/hub
causing a global or selective suspend condition.
5 RESRIFG RW 0h Resume request bit. This bit is set by hardware in response to the host/hub
causing a resume event.
4-3 Reserved R 0h Reserved. Always reads as 0.
2 SETUPIFG RW 0h Setup transaction received bit. This bit is set by hardware when a SETUP
transaction is received. As long as this bit is set, transactions on IN and OUT on
endpoint-0 receive a NAK, regardless of their corresponding NAK bit value.
1 Reserved R 0h Reserved. Always reads as 0.
0 STPOWIFG RW 0h Setup overwrite bit. This bit is set by hardware when a setup packet is received
while there is already a packet in the setup buffer.

1.4.2.16 USBFUNADR Register

USB Function Address Register

Figure 1-30. USBFUNADR Register

7 6 5 4 3 2 1 0
Reserved FA6 FA5 FA4 FA3 FA2 FA1 FA0
r0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0
Can be modified only when USBEN = 1

Table 1-29. USBFUNADR Register Description

Bit Field Type Reset Description
7 Reserved R 0h Reserved. Always reads as 0.
6-0 FA[6:0] RW 0h Function address (USB address 0 to 127). These bits define the current device
address assigned to this USB device. Software must write a value from 0 to 127
when a Set-Address command is received from the host.

46 USB Module SLAU284F – August 2012 – Revised March 2018

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1.4.3 USB Buffer Registers and Memory

The data buffers for all endpoints, as well as the registers that define endpoints 1 to 7, are stored in the
USB RAM buffer memory. Doing so allows for efficient and flexible use of this memory. The memory area
is known as the USB buffer memory, and the registers that define its use are the buffer descriptor
registers.
The buffer memory blocks are listed in Table 1-30. The registers are listed in Table 1-31. All addresses
are expressed as offsets; the base address can be found in the device-specific data sheet.
All memory is byte and word accessible.

Table 1-30. USB Buffer Memory

Offset Acronym Memory Type
0000h USBSTABUFF Start of buffer space Read/Write
⋮ ⋮ 1904 bytes of configurable buffer space ⋮
076Fh USBTOPBUFF End of buffer space Read/Write
0770h Read/Write
⋮ USBOEP0BUF Output endpoint_0 buffer ⋮
0777h Read/Write
0778h Read/Write
⋮ USBIEP0BUF Input endpoint_0 buffer ⋮
077Fh Read/Write
0780h Read/Write
⋮ USBSUBLK Setup Packet Block ⋮
0787h Read/Write

Table 1-31. USB Buffer Descriptor Registers

Offset Acronym Register Name Type Section
0788h USBOEPCNF_1 Output Endpoint_1 Configuration Register Read/Write Section 1.4.3.1
0789h USBOEPBBAX_1 Output Endpoint_1 X Buffer Base Address Register Read/Write Section 1.4.3.2
078Ah USBOEPBCTX_1 Output Endpoint_1 X Byte Count Register Read/Write Section 1.4.3.3
078Dh USBOEPBBAY_1 Output Endpoint_1 Y Buffer Base Address Register Read/Write Section 1.4.3.4
078Eh USBOEPBCTY_1 Output Endpoint_1 Y Byte Count Register Read/Write Section 1.4.3.5
078Fh USBOEPSIZXY_1 Output Endpoint_1 X and Y Buffer Size Register Read/Write Section 1.4.3.6
0790h USBOEPCNF_2 Output Endpoint_2 Configuration Register Read/Write Section 1.4.3.1
0791h USBOEPBBAX_2 Output Endpoint_2 X Buffer Base Address Register Read/Write Section 1.4.3.2
0792h USBOEPBCTX_2 Output Endpoint_2 X Byte Count Register Read/Write Section 1.4.3.3
0795h USBOEPBBAY_2 Output Endpoint_2 Y Buffer Base Address Register Read/Write Section 1.4.3.4
0796h USBOEPBCTY_2 Output Endpoint_2 Y Byte Count Register Read/Write Section 1.4.3.5
0797h USBOEPSIZXY_2 Output Endpoint_2 X and Y Buffer Size Register Read/Write Section 1.4.3.6
0798h USBOEPCNF_3 Output Endpoint_3 Configuration Register Read/Write Section 1.4.3.1
0799h USBOEPBBAX_3 Output Endpoint_3 X Buffer Base Address Register Read/Write Section 1.4.3.2
079Ah USBOEPBCTX_3 Output Endpoint_3 X Byte Count Register Read/Write Section 1.4.3.3
079Dh USBOEPBBAY_3 Output Endpoint_3 Y Buffer Base Address Register Read/Write Section 1.4.3.4
079Eh USBOEPBCTY_3 Output Endpoint_3 Y Byte Count Register Read/Write Section 1.4.3.5
079Fh USBOEPSIZXY_3 Output Endpoint_3 X and Y Buffer Size Register Read/Write Section 1.4.3.6

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Table 1-31. USB Buffer Descriptor Registers (continued)

Offset Acronym Register Name Type Section
07A0h USBOEPCNF_4 Output Endpoint_4 Configuration Register Read/Write Section 1.4.3.1
07A1h USBOEPBBAX_4 Output Endpoint_4 X Buffer Base Address Register Read/Write Section 1.4.3.2
07A2h USBOEPBCTX_4 Output Endpoint_4 X Byte Count Register Read/Write Section 1.4.3.3
07A5h USBOEPBBAY_4 Output Endpoint_4 Y Buffer Base Address Register Read/Write Section 1.4.3.4
07A6h USBOEPBCTY_4 Output Endpoint_4 Y Byte Count Register Read/Write Section 1.4.3.5
07A7h USBOEPSIZXY_4 Output Endpoint_4 X and Y Buffer Size Register Read/Write Section 1.4.3.6
07A8h USBOEPCNF_5 Output Endpoint_5 Configuration Register Read/Write Section 1.4.3.1
07A9h USBOEPBBAX_5 Output Endpoint_5 X Buffer Base Address Register Read/Write Section 1.4.3.2
07AAh USBOEPBCTX_5 Output Endpoint_5 X Byte Count Register Read/Write Section 1.4.3.3
07ADh USBOEPBBAY_5 Output Endpoint_5 Y Buffer Base Address Register Read/Write Section 1.4.3.4
07AEh USBOEPBCTY_5 Output Endpoint_5 Y Byte Count Register Read/Write Section 1.4.3.5
07AFh USBOEPSIZXY_5 Output Endpoint_5 X and Y Buffer Size Register Read/Write Section 1.4.3.6
07B0h USBOEPCNF_6 Output Endpoint_6 Configuration Register Read/Write Section 1.4.3.1
07B1h USBOEPBBAX_6 Output Endpoint_6 X Buffer Base Address Register Read/Write Section 1.4.3.2
07B2h USBOEPBCTX_6 Output Endpoint_6 X Byte Count Register Read/Write Section 1.4.3.3
07B5h USBOEPBBAY_6 Output Endpoint_6 Y Buffer Base Address Register Read/Write Section 1.4.3.4
07B6h USBOEPBCTY_6 Output Endpoint_6 Y Byte Count Register Read/Write Section 1.4.3.5
07B7h USBOEPSIZXY_6 Output Endpoint_6 X and Y Buffer Size Register Read/Write Section 1.4.3.6
07B8h USBOEPCNF_7 Output Endpoint_7 Configuration Register Read/Write Section 1.4.3.1
07B9h USBOEPBBAX_7 Output Endpoint_7 X Buffer Base Address Register Read/Write Section 1.4.3.2
07BAh USBOEPBCTX_7 Output Endpoint_7 X Byte Count Register Read/Write Section 1.4.3.3
07BDh USBOEPBBAY_7 Output Endpoint_7 Y Buffer Base Address Register Read/Write Section 1.4.3.4
07BEh USBOEPBCTY_7 Output Endpoint_7 Y Byte Count Register Read/Write Section 1.4.3.5
07BFh USBOEPSIZXY_7 Output Endpoint_7 X and Y Buffer Size Register Read/Write Section 1.4.3.6
07C8h USBIEPCNF_1 Input Endpoint_1 Configuration Register Read/Write Section 1.4.3.7
07C9h USBIEPBBAX_1 Input Endpoint_1 X Buffer Base Address Register Read/Write Section 1.4.3.8
07CAh USBIEPBCTX_1 Input Endpoint_1 X Byte Count Register Read/Write Section 1.4.3.9
07CDh USBIEPBBAY_1 Input Endpoint_1 Y Buffer Base Address Register Read/Write Section 1.4.3.10
07CEh USBIEPBCTY_1 Input Endpoint_1 Y Byte Count Register Read/Write Section 1.4.3.11
07CFh USBIEPSIZXY_1 Input Endpoint_1 X and Y Buffer Size Register Read/Write Section 1.4.3.12
07D0h USBIEPCNF_2 Input Endpoint_2 Configuration Register Read/Write Section 1.4.3.7
07D1h USBIEPBBAX_2 Input Endpoint_2 X Buffer Base Address Register Read/Write Section 1.4.3.8
07D2h USBIEPBCTX_2 Input Endpoint_2 X Byte Count Register Read/Write Section 1.4.3.9
07D5h USBIEPBBAY_2 Input Endpoint_2 Y Buffer Base Address Register Read/Write Section 1.4.3.10
07D6h USBIEPBCTY_2 Input Endpoint_2 Y Byte Count Register Read/Write Section 1.4.3.11
07D7h USBIEPSIZXY_2 Input Endpoint_2 X and Y Buffer Size Register Read/Write Section 1.4.3.12
07D8h USBIEPCNF_3 Input Endpoint_3 Configuration Register Read/Write Section 1.4.3.7
07D9h USBIEPBBAX_3 Input Endpoint_3 X Buffer Base Address Register Read/Write Section 1.4.3.8
07DAh USBIEPBCTX_3 Input Endpoint_3 X Byte Count Register Read/Write Section 1.4.3.9
07DDh USBIEPBBAY_3 Input Endpoint_3 Y Buffer Base Address Register Read/Write Section 1.4.3.10
07DEh USBIEPBCTY_3 Input Endpoint_3 Y Byte Count Register Read/Write Section 1.4.3.11
07DFh USBIEPSIZXY_3 Input Endpoint_3 X and Y Buffer Size Register Read/Write Section 1.4.3.12

48 USB Module SLAU284F – August 2012 – Revised March 2018

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Table 1-31. USB Buffer Descriptor Registers (continued)

Offset Acronym Register Name Type Section
07E0h USBIEPCNF_4 Input Endpoint_4 Configuration Register Read/Write Section 1.4.3.7
07E1h USBIEPBBAX_4 Input Endpoint_4 X Buffer Base Address Register Read/Write Section 1.4.3.8
07E2h USBIEPBCTX_4 Input Endpoint_4 X Byte Count Register Read/Write Section 1.4.3.9
07E5h USBIEPBBAY_4 Input Endpoint_4 Y Buffer Base Address Register Read/Write Section 1.4.3.10
07E6h USBIEPBCTY_4 Input Endpoint_4 Y Byte Count Register Read/Write Section 1.4.3.11
07E7h USBIEPSIZXY_4 Input Endpoint_4 X and Y Buffer Size Register Read/Write Section 1.4.3.12
07E8h USBIEPCNF_5 Input Endpoint_5 Configuration Register Read/Write Section 1.4.3.7
07E9h USBIEPBBAX_5 Input Endpoint_5 X Buffer Base Address Register Read/Write Section 1.4.3.8
07EAh USBIEPBCTX_5 Input Endpoint_5 X Byte Count Register Read/Write Section 1.4.3.9
07EDh USBIEPBBAY_5 Input Endpoint_5 Y Buffer Base Address Register Read/Write Section 1.4.3.10
07EEh USBIEPBCTY_5 Input Endpoint_5 Y Byte Count Register Read/Write Section 1.4.3.11
07EFh USBIEPSIZXY_5 Input Endpoint_5 X and Y Buffer Size Register Read/Write Section 1.4.3.12
07F0h USBIEPCNF_6 Input Endpoint_6 Configuration Register Read/Write Section 1.4.3.7
07F1h USBIEPBBAX_6 Input Endpoint_6 X Buffer Base Address Register Read/Write Section 1.4.3.8
07F2h USBIEPBCTX_6 Input Endpoint_6 X Byte Count Register Read/Write Section 1.4.3.9
07F5h USBIEPBBAY_6 Input Endpoint_6 Y Buffer Base Address Register Read/Write Section 1.4.3.10
07F6h USBIEPBCTY_6 Input Endpoint_6 Y Byte Count Register Read/Write Section 1.4.3.11
07F7h USBIEPSIZXY_6 Input Endpoint_6 X and Y Buffer Size Register Read/Write Section 1.4.3.12
07F8h USBIEPCNF_7 Input Endpoint_7 Configuration Register Read/Write Section 1.4.3.7
07F9h USBIEPBBAX_7 Input Endpoint_7 X Buffer Base Address Register Read/Write Section 1.4.3.8
07FAh USBIEPBCTX_7 Input Endpoint_7 X Byte Count Register Read/Write Section 1.4.3.9
07FDh USBIEPBBAY_7 Input Endpoint_7 Y Buffer Base Address Register Read/Write Section 1.4.3.10
07FEh USBIEPBCTY_7 Input Endpoint_7 Y Byte Count Register Read/Write Section 1.4.3.11
07FFh USBIEPSIZXY_7 Input Endpoint_7 X and Y Buffer Size Register Read/Write Section 1.4.3.12

SLAU284F – August 2012 – Revised March 2018 USB Module 49

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1.4.3.1 USBOEPCNF_n Register

Output Endpoint-n Configuration Register
This register can be modified only when USBEN = 1.

Figure 1-31. USBOEPCNF_n Register

7 6 5 4 3 2 1 0
UBME Reserved TOGGLE DBUF STALL USBIIE Reserved
rw r0 rw rw rw rw r0 r0
Can be modified only when USBEN = 1

Table 1-32. USBOEPCNF_n Register Description

Bit Field Type Reset Description
7 UBME RW 0h UBM out endpoint-n enable. This bit is to be set or cleared by software.
0b = UBM cannot use this endpoint
1b = UBM can use this endpoint
6 Reserved R 0h Reserved. Always reads as 0.
5 TOGGLE RW 0h Toggle bit. The toggle bit is controlled by the UBM and is toggled at the end of a
successful out data stage transaction, if a valid data packet is received and the
data packet's packet ID matches the expected packet ID.
4 DBUF RW 0h Double buffer enable. This bit can be set to enable the use of both the X and Y
data packet buffers for USB transactions, for a particular out endpoint. Clearing it
results in the use of single buffer mode. In this mode, only the X buffer is used.
0b = Primary buffer only (X-buffer only)
1b = Toggle bit selects buffer
3 STALL RW 0h USB stall condition. This bit can be set to cause endpoint transactions to be
stalled. When set, the hardware automatically returns a stall handshake to the
host for any transaction received on endpoint-0. The stall bit is cleared
automatically by the next setup transaction.
0b = Indicates no stall
1b = Indicates stall
2 USBIIE RW 0h USB transaction interrupt indication enable. Can be set or cleared to define if
interrupts are to be flagged in general. To generate an interrupt, the
corresponding interrupt flag must be set (OEPIE).
0b = Corresponding interrupt flag will not be set
1b = Corresponding interrupt flag will be set
1-0 Reserved R 0h Reserved. Always reads as 0.

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1.4.3.2 USBOEPBBAX_n Register

Output Endpoint-n X Buffer Base Address Register
This register can be modified only when USBEN = 1.

Figure 1-32. USBOEPBBAX_n Register

7 6 5 4 3 2 1 0
ADR
rw rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-33. USBOEPBBAX_n Register Description

Bit Field Type Reset Description
7-0 ADR RW 0h X-buffer base address. These are the upper eight bits of the X-buffer's base
address. The three LSBs are assumed to be zero, for a total of 11 bits. This
value needs to be set by software. The UBM uses this value as the start address
of a given transaction. It does not change this value at the end of a transaction.

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1.4.3.3 USBOEPBCTX_n Register

Output Endpoint-n X Byte Count Register
This register can be modified only when USBEN = 1.

Figure 1-33. USBOEPBCTX_n Register

7 6 5 4 3 2 1 0
NAK CNT
rw rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-34. USBOEPBCTX_n Register Description

Bit Field Type Reset Description
7 NAK RW 0h No-acknowledge status bit. The NAK status bit is set by the UBM at the end of a
successful USB out transaction to that endpoint, to indicate that the USB
endpoint-"n" buffer contains a valid data packet, and that the buffer data count
value is valid. When this bit is set, all subsequent transactions to that endpoint
result in a NAK handshake response to the USB host. To re-enable this endpoint
to receive another data packet from the host, this bit must be cleared.
0b = No valid data in buffer. The buffer is ready to receive OUT packets from the
host.
1b = The buffer contains a valid packet from the host, and it has not been picked
up (subsequent host-out requests receive a NAK)
6-0 CNT RW 0h X-buffer data count. The Out_EP-n data count value is set by the UBM when a
new data packet is written to the X-buffer for that out endpoint. It is set to the
number of bytes received in the data buffer.

1.4.3.4 USBOEPBBAY_n Register

Output Endpoint-n Y Buffer Base Address Register
This register can be modified only when USBEN = 1.

Figure 1-34. USBOEPBBAY_n Register

7 6 5 4 3 2 1 0
ADR
rw rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-35. USBOEPBBAY_n Register Description

Bit Field Type Reset Description
7-0 ADR RW 0h Y-buffer base address. These are the upper eight bits of the Y-buffer's base
address. The three LSBs are assumed to be zero, for a total of 11 bits. This
value needs to be set by software. The UBM uses this value as the start address
of a given transaction. It does not change this value at the end of a transaction.

52 USB Module SLAU284F – August 2012 – Revised March 2018

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1.4.3.5 USBOEPBCTY_n Register

Output Endpoint-n X Byte Count Register
This register can be modified only when USBEN = 1.

Figure 1-35. USBOEPBCTY_n Register

7 6 5 4 3 2 1 0
NAK CNT
rw rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-36. USBOEPBCTY_n Register Description

Bit Field Type Reset Description
7 NAK RW 0h No-acknowledge status bit. The NAK status bit is set by the UBM at the end of a
successful USB out transaction to that endpoint, to indicate that the USB
endpoint-"n" buffer contains a valid data packet, and that the buffer data count
value is valid. When this bit is set, all subsequent transactions to that endpoint
result in a NAK handshake response to the USB host. To re-enable this endpoint
to receive another data packet from the host, this bit must be cleared.
0b = No valid data in buffer. The buffer is ready to receive OUT packets from the
host.
1b = The buffer contains a valid packet from the host, and it has not been picked
up (subsequent host-out requests receive a NAK)
6-0 CNT RW 0h Y-buffer data count. The Out_EP-n data count value is set by the UBM when a
new data packet is written to the X-buffer for that out endpoint. It is set to the
number of bytes received in the data buffer.

1.4.3.6 USBOEPSIZXY_n Register

Output Endpoint-n X and Y Buffer Size Register
This register can be modified only when USBEN = 1.

Figure 1-36. USBOEPSIZXY_n Register

7 6 5 4 3 2 1 0
Reserved SIZx
r0 rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-37. USBOEPSIZXY_n Register Description

Bit Field Type Reset Description
7 Reserved R 0h Reserved. Always reads as 0.
6-0 SIZx RW 0h Buffer size count. This value needs to be set by software to configure the size of
the X and Y data packet buffers. Both buffers are set to the same size, based on
this value.
000:0000b to 100:0000b are valid numbers for 0 to 64 bytes.
Any value greater than or equal to 100:0001b results in unpredictable results.

SLAU284F – August 2012 – Revised March 2018 USB Module 53

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1.4.3.7 USBIEPCNF_n Register

Input Endpoint-n Configuration Register
This register can be modified only when USBEN = 1.

Figure 1-37. USBIEPCNF_n Register

7 6 5 4 3 2 1 0
UBME Reserved TOGGLE DBUF STALL USBIIE Reserved
rw r0 rw rw rw rw r0 r0
Can be modified only when USBEN = 1

Table 1-38. USBIEPCNF_n Register Description

Bit Field Type Reset Description
7 UBME RW 0h UBM in endpoint-n enable. This value needs to be set or cleared by software.
0b = UBM cannot use this endpoint
1b = UBM can use this endpoint
6 Reserved R 0h Reserved. Always reads as 0.
5 TOGGLE RW 0h Toggle bit. The toggle bit is controlled by the UBM and is toggled at the end of a
successful in data stage transaction, if a valid data packet is transmitted. If this
bit is cleared, a DATA0 packet ID is transmitted in the data packet to the host. If
this bit is set, a DATA1 packet ID is transmitted in the data packet.
4 DBUF RW 0h Double buffer enable. This bit can be set to enable the use of both the X and Y
data packet buffers for USB transactions, for a particular out endpoint. Clearing it
results in the use of single buffer mode. In this mode, only the X buffer is used.
0b = Primary buffer only (X-buffer only)
1b = Toggle bit selects buffer
3 STALL RW 0h USB stall condition. This bit can be set to cause endpoint transactions to be
stalled. When set, the hardware automatically returns a stall handshake to the
host for any transaction received on endpoint-0. The stall bit is cleared
automatically by the next setup transaction.
0b = Indicates no stall
1b = Indicates stall
2 USBIIE RW 0h USB transaction interrupt indication enable. Can be set or cleared to define if
interrupts are to be flagged in general. To generate an interrupt the
corresponding interrupt flag must be set (OEPIE).
0b = Corresponding interrupt flag will not be set
1b = Corresponding interrupt flag will be set
1-0 Reserved R 0h Reserved. Always reads as 0.

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1.4.3.8 USBIEPBBAX_n Register

Input Endpoint-n X Buffer Base Address Register
This register can be modified only when USBEN = 1.

Figure 1-38. USBIEPBBAX_n Register

7 6 5 4 3 2 1 0
ADR
rw rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-39. USBIEPBBAX_n Register Description

Bit Field Type Reset Description
7-0 ADR RW 0h X-buffer base address. These are the upper eight bits of the X-buffer's base
address. The three LSBs are assumed to be zero, for a total of 11 bits. This
value needs to be set by software. The UBM uses this value as the start address
of a given transaction. It does not change this value at the end of a transaction.

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1.4.3.9 USBIEPBCTX_n Register

Input Endpoint-n X Byte Count Register
This register can be modified only when USBEN = 1.

Figure 1-39. USBIEPBCTX_n Register

7 6 5 4 3 2 1 0
NAK CNT
rw rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-40. USBIEPBCTX_n Register Description

Bit Field Type Reset Description
7 NAK RW 0h No-acknowledge status bit. The NAK status bit is set by the UBM at the end of a
successful USB in transaction from that endpoint, to indicate that the EP-n in
buffer is empty. For interrupt or bulk endpoints, when this bit is set, all
subsequent transactions from that endpoint result in a NAK handshake response
to the USB host. To re-enable this endpoint to transmit another data packet to
the host, this bit must be cleared.
0b = Buffer contains a valid data packet for the host
1b = Buffer is empty (any host-In requests receive a NAK)
6-0 CNT RW 0h X-buffer data count. The In_EP-n X-buffer data count value must be set by
software when a new data packet is written to the buffer. It should be the number
of bytes in the data packet for interrupt, or bulk endpoint transfers.
000:0000b to 100:0000b are valid numbers for 0 to 64 bytes.
Any value greater than or equal to 100:0001b results in unpredictable results.

1.4.3.10 USBIEPBBAY_n Register

Input Endpoint-n Y Buffer Base Address Register
This register can be modified only when USBEN = 1.

Figure 1-40. USBIEPBBAY_n Register

7 6 5 4 3 2 1 0
ADR
rw rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-41. USBIEPBBAY_n Register Description

Bit Field Type Reset Description
7-0 ADR RW 0h Y-buffer base address. These are the upper eight bits of the Y-buffer's base
address. The three LSBs are assumed to be zero, for a total of 11 bits. This
value needs to be set by software. The UBM uses this value as the start address
of a given transaction. It does not change this value at the end of a transaction.

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1.4.3.11 USBIEPBCTY_n Register

Input Endpoint-n Y Byte Count Register
This register can be modified only when USBEN = 1.

Figure 1-41. USBIEPBCTY_n Register

7 6 5 4 3 2 1 0
NAK CNT
rw rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-42. USBIEPBCTY_n Register Description

Bit Field Type Reset Description
7 NAK RW 0h No-acknowledge status bit. The NAK status bit is set by the UBM at the end of a
successful USB in transaction from that endpoint, to indicate that the EP-n in
buffer is empty. For interrupt or bulk endpoints, when this bit is set, all
subsequent transactions from that endpoint result in a NAK handshake response
to the host. To re-enable this endpoint to transmit another data packet to the
host, this bit must be cleared. This bit is set by USB SW-init.
0b = Buffer contains a valid data packet for host device
1b = Buffer is empty (any host-in requests receive a NAK)
6-0 CNT RW 0h Y-Buffer data count. The In EP-n Y-buffer data count value needs to be set by
software when a new data packet is written to the buffer. It should be the number
of bytes in the data packet for interrupt, or bulk endpoint transfers.
000:0000b to 100:0000b are valid numbers for 0 to 64 bytes.
Any value greater than or equal to 100:0001b results in unpredictable results.

1.4.3.12 USBIEPSIZXY_n Register

Input Endpoint-n X and Y Buffer Size Register
This register can be modified only when USBEN = 1.

Figure 1-42. USBIEPSIZXY_n Register

7 6 5 4 3 2 1 0
Reserved SIZ
r0 rw rw rw rw rw rw rw
Can be modified only when USBEN = 1

Table 1-43. USBIEPSIZXY_n Register Description

Bit Field Type Reset Description
7 Reserved R 0h Reserved. Always reads as 0.
6-0 RW 0h Buffer size count. This value needs to be set by software to configure the size of
the X and Y data packet buffers. Both buffers are set to the same size, based on
this value.
000:0000b to 100:0000b are valid numbers for 0 to 64 bytes.
Any value greater than or equal to 100:0001b results in unpredictable results.

SLAU284F – August 2012 – Revised March 2018 USB Module 57

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