UNIT 2

ARM7 BASED MICROCONTROLLER

Prof. Vaishali Gongane

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Syllabus

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Architecture

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 Applications
• The ARM7TDMI-S: Thumb, makes it ideally
suited for high-volume applications with memory
restrictions, or where code density is an issue.
• Due to their tiny size and low power
consumption, ideal forapplications where
miniaturization is a key requirement.
•Communication gateways and Protocol converters
•Modems ,Voice recognition, Low end Imaging
•Industrial control and Medical systems.

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BUSES

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Bus Structure

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 Bus Structure
• In LPC2148 three types of busses are used to connect
the core with other peripherals on chip.
1. Local Bus to connect the on chip memory controllers
and fast GPIO’s
2. AMBA Advance High Performance Bus (AHB) for
interrupt controller
• AHB (Advanced High Performance BUS)
-High performance
-Support pipelined
- Each AHB peripheral is allocated a 16 kB address space
within the AHB address space.

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 Bus Structure
2. VLSI Peripheral Bus (VPB) for other on chip
peripherals.
•VPB(VLSI Peripheral bus )
-Low power
-Non pipelined
-Simple interface
AHB acts as a bridge for VPB.
•VPB is mainly meant for connect slower peripherals than
that of processor.
•VPB can drive the peripherals at ¼ CPU clock frequency.
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System Control LPC 2148

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 Example
Development board has 12MHz crystal
frequency. The CPU clock frequency to be
achieved is 60MHz.
• Find M= CCLK/Fosc = 60×106/12×106 = 5
• 156<FCCO<320 = CCLK × 2× P
= 60 × 2× P
P= 156/120= 1.3 P= 320/120=2.67
P must be an integer between 1.3 and 2.67, so
P=2
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• PLLCFG

7 6 5 4 3 2 1 0
R PSEL PSEL MSEL MSEL MSEL MSEL MSEL
0 0 1 0 0 1 0 0

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 Pin Connect Block
• The pin connect block allows selected pins of the
microcontroller to have more than one function.
• Configuration registers control the multiplexers to allow
connection between the pin and the on chip peripherals.
• Peripherals should be connected to the appropriate pins prior
to being activated, and prior to any related interrupt(s) being
enabled.
• Activity of any enabled peripheral function that is not mapped
to a related pin should be considered undefined.
• Selection of a single function on a port pin completely
excludes all other functions otherwise available on the same
pin.

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 PINSEL
• To enable pin functions three 32 bit PINSEL registers: PINSEL0,
PINSEL1 and PINSEL2 are used
• PINSEL0 contains GPIO pins P0.0 to P0.15
• PINSEL1 contains GPIO pins P0.16 to P0.31
• PINSEL2 is a special case, and is used to control whether pins
P1.16...31 are used as GPIO pins, or as a Debug port in
combination with a hardware JTAG debugger.
• Each associated 'pin' in PINSEL0 and PINSEL1 is assigned a 2-bit
address.
• P0.0, for example, uses the first two bits in PINSEL0, P0.1 uses the
next two bits, and so on, until you end up with the following layout:

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• The PINSEL registers control the functions of
device pins as shown below.
Pairs of bits in these registers correspond to
specific device pins.
00: Primary (default) function, typically GPIO
01: First alternate function
10: Second alternate function 11: Reserved

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 Example to select the functionality of
Pin
• P0.0 00 GPIO Port 0.0 01 TXD (UART0) 10
PWM1
11 Reserved
• If we want to choose P0.0 as TXD then we have
to write
PINSEL0=0x00000001
• If we want to choose P0.0 as PWM1 then write
PINSEL0=0x00000002

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ARM Memory
Organization

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 Effect of
• The ARM can beendianess
set up to access its data in either
little or big endian format.
• Little endian:
– Least significant byte of a word is stored in bits 0-7
of an addressed word.
• Big endian:
– Least significant byte of a word is stored in bits 24-
31 of an addressed word.
• This has no real relevance unless data is stored as
words and then accessed in smaller sized
quantities (halfwords or bytes).
– Which byte / halfword is accessed will depend on the
endianess of the system involved.
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 Endianess
Example
r0 = 0x11223344
31 24 23 16 15 87
0

11 22 33 44

STR r0, [r1]

31 24 23 16 15 87 31 24 23 16 15 8 0
0 7
r1 = 0x100 Memory r1 = 0x100
11 22 33 44 44 33 22 11

Little-endian LDRB r2, [r1] Big-endian

31 24 23 16 15 8 0 31 24 23 16 15 8 0
7 7

00 00 00 44 00 00 00 11
r2 = 0x44 r2 = 0x11

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 GPIO
Registers

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Example

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 Problem
• Write the configuration of GPIO registers for
interfacing 8 LEDs connected to P0. 19 to
P0.26.
• Write the configuration of GPIO registers for
interfacing LEDs connected to P1. 16, P1. 18,
P1. 20, P1. 22.

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 Count Control Register (CTCR, TIMER0: T0CTCR
and TIMER1: T1CTCR

• The Count Control Register (CTCR) is used to select

between Timer and Counter mode, and in Counter mode to
select the pin and edge(s) for
• When Counter Mode is chosen as a mode of operation, the
CAP input (selected by the CTCR bits 3:2) is sampled on
every rising edge of the PCLK clock. After comparing two
consecutive samples of this CAP input, one of the following
four events is recognized:
• rising edge, falling edge, either of edges or no changes in
the level of the selected CAP input.
• Only if the identified event corresponds to the one selected
by bits 1:0 in the CTCR register, the Timer Counter register
will be incremented. counting.

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Count Control Register (CTCR, TIMER0: T0CTCR - and
TIMER1: T1CTCR

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 Timer
Features

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 Timer
Registers

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Steps to configure the timer

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Prescale calculations

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 Basic LED Blinking code using
Timers
#include <lpc214x.h>
#define PRESCALE 60000 //60000 PCLK clock
cycles to increment TC by 1

void delayMS(unsigned int milliseconds);

void initTimer0(void);

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 Using Match register
void delay_ MR()
{
T0CTCR=0X0000; //Timer Mode T0PR=59999; //Prescaler Value
T0MR0=1000; //Match Register Value
T0MCR=0x00000004; //TC and PC will be stopped and TCR[0] will
be set to 0 if MR0 matches the TC.
T0TCR=0X02; //Reset Timer T0TCR=0X01; //Timer ON
while(T0TC!=T0MR0);
T0TCR=0; //Timer OFF

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LED Interfacing with LPC2148
Schematic Diagram

88
PCLK= 15 MHz
Considering a delay of 1 ms

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void init_timer() void delay(unsigned int n)
{ {
T0CTCR = 0x0; T0TCR=0x02;
T0PR = 14999; T0TCR=0x01;
T0TCR = 0x02; while (T0TC < n);
} T0TCR=0x00;
}

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#include<lpc214x.h> int main(void)
{
init_timer();
IO0DIR = 0xFFFFFFFF;
while(1)
{ IO0SET = 0xFFFFFFFF; //Turn on LEDs
delay(1000);
IO0CLR = 0xFFFFFFFF; //Turn them off
delay(1000);
}

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