Introduction STM32 Analog do Digital Converter ADC registers
Outline
1 Introduction
Introduction to Analog to Digital Converters
Analog to Digital Converter types
Analog to Digital Converter characteristics
2 STM32 Analog do Digital Converter
Introduction
Features
ADC and DMA
3 ADC registers
Overview
Introduction STM32 Analog do Digital Converter ADC registers
Introduction to Analog to Digital Converters (1/2)
Definition
An analog-to-digital converter is a device that converts a continuous
quantity to a discrete time digital representation
Introduction STM32 Analog do Digital Converter ADC registers
Introduction to Analog to Digital Converters (2/2)
Introduction STM32 Analog do Digital Converter ADC registers
Continuous quantity to discrete quantity (1/2)
N = 2n
LSB = VREF /2n
Introduction STM32 Analog do Digital Converter ADC registers
Continuous quantity to discrete quantity (2/2)
Introduction STM32 Analog do Digital Converter ADC registers
Continuous time to discrete time (1/2)
Introduction STM32 Analog do Digital Converter ADC registers
Continuous time to discrete time (2/2)
Nyquist rate
The Nyquist rate is the minimum sampling rate required to avoid
aliasing, equal to twice the highest frequency contained within the signal.
def
fN = 2B
Minimum sampling rate
To avoid aliasing, the sampling rate must exceed the Nyquist rate.
fS > fN
Introduction STM32 Analog do Digital Converter ADC registers
Analog to Digital Converter diagram
Introduction STM32 Analog do Digital Converter ADC registers
FLASH Analog to Digital Converter
Introduction STM32 Analog do Digital Converter ADC registers
SAR Analog to Digital Converter
Introduction STM32 Analog do Digital Converter ADC registers
Sigma-delta Analog to Digital Converter
Introduction STM32 Analog do Digital Converter ADC registers
Analog to Digital Converter characteristics
Resolution
Max sampling rate
Signal to Noise Ratio (SNR)
Input voltage offset
Gain stability
Linearity
Introduction STM32 Analog do Digital Converter ADC registers
Gain error
Introduction STM32 Analog do Digital Converter ADC registers
Voltage offset error
Introduction STM32 Analog do Digital Converter ADC registers
Non-linearity errors
Introduction STM32 Analog do Digital Converter ADC registers
Outline
1 Introduction
Introduction to Analog to Digital Converters
Analog to Digital Converter types
Analog to Digital Converter characteristics
2 STM32 Analog do Digital Converter
Introduction
Features
ADC and DMA
3 ADC registers
Overview
Introduction STM32 Analog do Digital Converter ADC registers
STM32 Analog do Digital Converter
Successive approximation analog-to-digital converter
12-bit resolution
Interrupt generation at End of Conversion, End of Injected
conversion and Analog watchdog event
Single and continuous conversion modes
Scan mode for automatic conversion of channel 0 to channel n
Self-calibration
External trigger option for both regular and injected conversion
Total conversion time: 14 to 252 TCK (tS for sampling + 12.5 for
successive approximation)
Introduction STM32 Analog do Digital Converter ADC registers
STM32 Analog do Digital Converter accuracy
Introduction STM32 Analog do Digital Converter ADC registers
Analog power supply
Introduction STM32 Analog do Digital Converter ADC registers
STM32 clock tree
Introduction STM32 Analog do Digital Converter ADC registers
STM32 Analog do Digital Converter diagram
Introduction STM32 Analog do Digital Converter ADC registers
Channel selection
16 multiplexed channels
It is possible to organize the conversions in groups
A group consists of a sequence of conversions which can be done on
any channel and in any order
Regular group:
up to 16 conversions
the conversion sequence must be selected in the ADC SQRx registers
Injected group:
up to 4 conversions
This mode is intended for use when conversion is triggered by an
external event or by software
The injected group has priority over the regular channel group
It interrupts the conversion of the current channel in the regular
channel group
Introduction STM32 Analog do Digital Converter ADC registers
Single and continuous conversion mode
In Single conversion mode the ADC does one conversion
In Continuous mode (CONT = 1) another conversion starts as soon
as it finishes one
The conversion is started either by setting the ADON bit or by
external trigger
If the EOCIE is set, an interrupt is generated at the end of each
conversion
Introduction STM32 Analog do Digital Converter ADC registers
Scan conversion mode
Scans a group of analog channels
A single conversion is performed for each channel of the group
After each end of conversion the next channel of the group is
converted automatically
If CONT = 1, on last channel conversion, the ADC starts again
from the first group channel
If the DMA bit is set, the direct memory access controller is used to
transfer the converted data to SRAM after each EOC
Introduction STM32 Analog do Digital Converter ADC registers
Analog watchdog
The AWD analog watchdog status bit is set if the analog voltage
converted by the ADC is below a low threshold or above a high
threshold
These thresholds are programmed in the 12 least significant bits of
the ADC HTR and ADC LTR 16-bit registers
An interrupt can be enabled by using the AWDIE bit in the
ADC CR1 register
Introduction STM32 Analog do Digital Converter ADC registers
Direct Memory Access
Introduction STM32 Analog do Digital Converter ADC registers
ADC and DMA
Converted regular channels value are stored in a unique data register
It is necessary to use DMA for conversion of more than one regular
channel
The end of conversion of a regular channel generates a DMA request
Converted data is transferred from the ADC DR register to the
destination location selected by the user
Introduction STM32 Analog do Digital Converter ADC registers
Outline
1 Introduction
Introduction to Analog to Digital Converters
Analog to Digital Converter types
Analog to Digital Converter characteristics
2 STM32 Analog do Digital Converter
Introduction
Features
ADC and DMA
3 ADC registers
Overview
Introduction STM32 Analog do Digital Converter ADC registers
ADC status register (ADC SR)
0 AWD: Analog watchdog flag
This bit is set by hardware when the converted voltage crosses the values programmed
in the ADC LTR and ADC HTR registers. It is cleared by software.
0: No Analog watchdog event occurred
1: Analog watchdog event occurred
1 EOC: End of conversion
This bit is set by hardware at the end of a group channel conversion (regular or
injected). It is cleared by software or by reading the ADC DR.
0: Conversion is not complete
1: Conversion complete
4 STRT: Regular channel start flag
This bit is set by hardware when regular channel conversion starts. It is cleared by
software.
0: No regular channel conversion started
1: Regular channel conversion has started
Introduction STM32 Analog do Digital Converter ADC registers
ADC control register 1 (ADC CR1)
4:0 AWDCH[4:0]: Analog watchdog channel select bits
These bits are set and cleared by software. They select the input channel to be guarded
by the Analog watchdog.
00000: ADC analog input Channel0
...
10001: ADC analog input Channel17
5 EOCIE: Interrupt enable for EOC
This bit is set and cleared by software to enable/disable the End of Conversion interrupt.
0: EOC interrupt disabled
1: EOC interrupt enabled. An interrupt is generated when the EOC bit is set.
8 SCAN: Scan mode
This bit is set and cleared by software to enable/disable Scan mode. In Scan mode, the
inputs selected through the ADC SQRx or ADC JSQRx registers are converted.
0: Scan mode disabled
1: Scan mode enabled
Introduction STM32 Analog do Digital Converter ADC registers
ADC control register 2 (ADC CR2)
0 ADON: A/D converter ON/OFF
If this bit holds a value of zero and a 1 is written to it then it wakes up the ADC from
Power Down state.
Conversion starts when this bit holds a value of 1 and a 1 is written to it.
0: Disable ADC conversion and go to power down mode.
1: Enable ADC and to start conversion
1 CONT: Continuous conversion
0: Single conversion mode
1: Continuous conversion mode
8 DMA: Direct memory access mode
0: DMA mode disabled
1: DMA mode enabled
11 ALIGN: Data alignment
0: Right Alignment
1: Left Alignment
Introduction STM32 Analog do Digital Converter ADC registers
ADC sample time register 1 (ADC SMPR1)
4:0 SMPx[2:0]: Channel x Sample time selection
These bits are written by software to select the sample time individually for each
channel.
000: 1.5 cycles
001: 7.5 cycles
010: 13.5 cycles
011: 28.5 cycles
100: 41.5 cycles
101: 55.5 cycles
110: 71.5 cycles
111: 239.5 cycles
Introduction STM32 Analog do Digital Converter ADC registers
ADC regular sequence register 1 (ADC SQR1)
19:15 SQ16[4:0]: 16th conversion in regular sequence
These bits are written by software with the channel number (0..17) assigned as the 16th
in the conversion sequence.
23:20 L[3:0]: Regular channel sequence length
These bits are written by software to define the total number of conversions in the
regular channel conversion sequence.
0000: 1 conversion
0001: 2 conversions
...
1111: 16 conversions
Introduction STM32 Analog do Digital Converter ADC registers
ADC value registers
ADC regular data register (ADC DR)
ADC watchdog low threshold register (ADC LTR)
ADC watchdog low threshold register (ADC HTR)
References
http://en.wikipedia.org/wiki/Analog to digital converter
http://en.wikipedia.org/wiki/Sample and hold
http://en.wikipedia.org/wiki/Quantization error
http://en.wikipedia.org/wiki/Nyquist rate
http://en.wikipedia.org/wiki/Nyquist frequency
http://en.wikipedia.org/wiki/Flash ADC
http://en.wikipedia.org/wiki/Successive Approximation ADC
http://en.wikipedia.org/wiki/Sigma-delta modulation
STM32F10xxx Reference Manual (RM0008 - Doc ID 14611)
Application note: STM32 ADC modes and their applications (AN3116 - Doc ID
16840)
