AVR Microcontrollers- Introduction

Microprocessors, Lecture 3:

AVR Microcontrollers

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Widely-used microcontroller

Different familiesBased on the application and Flash memory capacity

Classic AVRe.g. AT90S2313, AT90S4433

Megae.g. ATmega8, ATmega32, ATmega128

Tinye.g. ATtiny13, ATtiny25

Special Purpose AVRe.g. AT90PWM216,AT90USB1287

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AVR internal architecture

PROGRAM ROM

PortsOSC

CPU

Timers

OtherPeripherals

ProgramBus Bus

RAM

I/O PINS

EEPROM

Interrupt Unit

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AVR’s CPU

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CPU:RISC architecture131 instructionsMost instructions are executed in a single cycle32 general-purpose registers64 IO registersMany useful peripherals

Very low-powerless than 10mW power consumption

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AVR’s CPU

AVR’s CPUALU

32 General Purpose registers (R0 to R31)

PC register

Instruction decoder

Almost the same for all families

CPUPC

ALU

registers

R1

R0

R15

R2

…

R16

R17

…

R30

R31

Instruction Register

Instruction decoder

SREG: I T H S V N CZ

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SREG flags

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Not all instructions affect flagsExample: load instruction has nothing to do with flags

Decision making by flags

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Memory address space

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A unified address space

32 general-purpose registersDirectly connected to the ALU

64 IO registersTo keep the data sent to/ received from peripherals

StackStarting from the end of SRAM and grow up to lower addressesIndexed by SPL-SPH registers

Internal busses

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Some simple instructions1. Loading values into the general purpose registers

LDI (Load Immediate)LDI Rd, k

Its equivalent in high level languages:

Rd = k

Example: LDI R16,53

R16 = 53

LDS (Load from SRAM)LDS R0,0x300Load R0 by data from address 300

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Some simple instructions2. Arithmetic calculation

There are some instructions for doing arithmetic and logic operations; such as:

ADD, SUB, MUL, AND, etc.

ADD Rd,RsRd = Rd + Rs

Example:

ADD R25, R9

R25 = R25 + R9

ADD R17,R30

R17 = R17 + R30

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Some simple instructions3. store

No immediate value store! Just stores can be done through registers

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Some simple instructions3. IN and OUT

Each IO register can be addressed in two ways:Memory addressIO address (relative to the beginning of the IO registers)

“IN” and “OUT” use the IO address

example: IN r1,0x16 ;// copy IO register no. 10 (memory address 0x36 to r1)

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Some other instructions

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ALU instructions

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Single operand instructions

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Directives

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Like directives in high level languages

For core readability

Not instructions that generate machine code after compile

Example: EQUTo set a constant valueEquivalent to CONSTANT in C++

Other directives

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AVR data size

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AVR just has 8-bit data

Programmer or compiler has to break larger data into 8-bit units

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A simple programWrite a program that calculates 19 + 95

LDI R16, 19 ;R16 = 19

LDI R20, 95 ;R20 = 95

ADD R16, R20 ;R16 = R16 + R20

CPUPC

ALU

registers

R1R0

R15

R2

…

R16R17

…

R30R31

Instruction Register

Instruction decoder

SREG: I T H S V N CZ

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Code memory

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The program after compiling is stored in a ROM (flash memory)

To keep the code even when the system is powered offData is stored in another memory (SRAM)

In AVR each code memory location is 2-bytes

In Atmega32, 32K flash memory is organized as 16Kx16 words

Needs 14-bit PC

Instruction size

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Almost all instructions are 2 bytesExample:

1110: machine code for LDIKkkk…= imidiate valuedddd= destination register

Another example

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32-bit instructions

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ATmega32

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16 MHz clock frequency44 pins32 KB instruction memory (Flash)1KB data memory (EEPROM)2048 B data memory (SRAM)SPI, USART, and I2C serial ports3 timers8 10-bit ADC channelsAnalog comparator4 PWM ports…….

ATMega32 pins

4 8-bit ports

PA, PB, PC, PD

Multiplexed with other in-outs

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AVR programming

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Assembly: AVR Studio

C: Code Vision