Microprocessor based Design for Biomedical Applications
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Microprocessor based Design for Biomedical Applications MBE 3 – MDBA III : The ATmega8 Basic Features (2) PowerPoint PPT Presentation

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Microprocessor based Design for Biomedical Applications MBE 3 – MDBA III : The ATmega8 Basic Features (2). Let‘s repeat some important topics of the last lecture: AVR memories SFRs – GFRs Bit Operations GPIO Ports Clock Sources Interrupt Handling. Today: Fix the IDE – Bug (update AVR-Studio)

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Microprocessor based Design for Biomedical Applications MBE 3 – MDBA III : The ATmega8 Basic Features (2)

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Microprocessor based Design for Biomedical ApplicationsMBE 3 – MDBAIII :The ATmega8Basic Features (2)

Let‘s repeat some important topics

of the last lecture:AVR memoriesSFRs – GFRsBit OperationsGPIO PortsClock SourcesInterrupt Handling

Today:Fix the IDE – Bug (update AVR-Studio)

Repeat blink.c source

Use the Simulator

Look at avr-gcc, avr-objdump, make

ISR – Interrupt Service Routines

Timer Interrupt Example

16-Bit Timer, ModesUART – Configuration and Modes

Start with Uart Example

Blink.c – sourcecode review

#include <avr/io.h>

#include <util/delay_basic.h>

#define Bit(x) (1<<x)

void delay_ms(uint16_t ms)


uint16_t t;

for (t=0;t<ms;t++)

_delay_loop_2(1843); // 1843 * 4 clock cycles gives 7372 cycles:

// (approx. 1 millisecond at 7,3728 MHz


int main( void )


DDRD = Bit(5); // DataDirection Port D: Pin D5 = Output (Led)

PORTD= Bit(5); // Switch on led and deactivate pullups on the inputs

while (1)


PORTD ^= Bit(5); // toggle D5

delay_ms(500); // wait 500 milliseconds




Include device specific definitions (SFRs,..)

Macro definition, shift left operation

Function definition, call by value

(call by reference: pointer)

SFRs for Port D configuration

Bit manipulation Port D (XOR)

Using the AVRStudio - Simulator

additional information to the Getting_Started.pdf

AVRStudio Simulator


Flow Control






AVRStudio Simulator



Watch Window

AVRStudio Simulator


Register and Memory Views

Watch Window

Disassembly Window

AVRStudio Simulator notes

● Select the Crystal / Oscillator frequency to get

accurate time measurements in the Simulator

●beware of delay loops (they take long to simulate)

● use „run to cursor“ or breakpoints for getting into

interrupt handlers

● on-chip debugging is useful,

needs devices with JTAG interface

or debugWire interface

Using the WinAVR-Toolchain from commandline

WinAVR-Toolchain – avr-gcc.exe



Convert .elf

to .ihex


to Device



and Linking


segment and



WinAVR-Toolchain – make.exe


The makefile

automates the build


only changed modules

are compiled



add flexibility

SRC = blink.c test.c

CFLAGS= -O2 -g -Wall

PRG = $(SRC:.c=.hex)

all: $(PRG)

# Create .hex files from .o files

%.hex : %.o

echo Creating $@

avr-objcopy -O ihex $< $@

# Compile

%.o : %.c

echo Compiling $@

avr-gcc $(CFLAGS) -mmcu=atmega8 $< -o $@


rm -f *~ *.bak *.lst *.o *.hexc

Variables &




current target

current prerequistite

Browse the GNU MAKE User Manual: http://www.gnu.org/software/make

WinAVR-Toolchain – avr-objdump.exe


Extract information

from .elf – file

Here: show



Where to find AVR C - specific information ?

● AVR-GCC is ANSI-C compatible

● browse the AVR Libc – Documentation

● examine module header files (#include <…>)

subdirectory avr/include

●use example code, play with open source firmware

Where to find AVR C - specific information ?

<assert.h>: Diagnostics

<ctype.h>: Character Operations

<errno.h>: System Errors

<inttypes.h>: Integer Type conversions

<math.h>: Mathematics

<stdint.h>: Standard Integer Types

<stdio.h>: Standard IO facilities

<stdlib.h>: General utilities

<string.h>: Strings, memory functions

<avr/boot.h>: Bootloader Support Utilities

<avr/eeprom.h>: EEPROM handling

<avr/interrupt.h>: Interrupts

<avr/pgmspace.h>: Program Space Utilities

<avr/power.h>: Power Reduction Management

<avr/io.h>: Special function registers and IO definitions

<avr/sleep.h>: Power Management and Sleep Modes

<util/delay_basic.h>: Basic busy-wait delay loops

<util/parity.h>: Parity bit generation

<util/twi.h>: TWI bit mask definitions

Useful modules,

all documented in

the AVR-Libc manual !

Where to find AVR C - specific information ?

Standard integer and character types, defined in <stdint.h>:

8, 16, 32 and 64 bit, signed and unsigned

• typedef signed char int8_t

• typedef unsigned char uint8_t

• typedef signed int int16_t

• typedef unsigned int uint16_t

• typedef signed long int int32_t

• typedef unsigned long int uint32_t

• typedef signed long long int int64_t

• typedef unsigned long long int uint64_t

#define INT8_MAX 0x7f

#define INT8_MIN (-INT8_MAX - 1)

Constants for

min and max values

Where to find AVR C - specific information ?

Some functions from <string.h>:

• void memcpy (void , const void , size_t)

• void memmove (void , const void , size_t)

• char strcat (char , const char )

• char strstr (const char , const char )

• char strupr (char )

Interrupt handling with the AVR-Libc API

Interrupt and Signal definitions:<avr/interrupt.h>

● remember: vector table points to interrupt routines

● by using the appropriate name, your routine will be

installed in the table and called when the interrupt occurs

● a set of default interrupt routines is provided

● Macro for registering interrupt routines: ISR (<signalname>)

● saving and restoring registers is handled

Interrupt handling with the AVR-Libc API

Examle interrupt handler for the ADC:

#include <avr/interrupt.h>



// user code here


● The interrupt source, here the ADC, has to be configured and enabled using SFRs

● Global interrupt instructions: sei () … set interupt enable

(I – bit in SREG) cli () … clear interrupt enable

● AVR hardware clears the global interrupt flag before entering an

interrupt vector -> use sei() to enable nested interrupts

Interrupt handling with the AVR-Libc API

Useful Interrupt vector names for ATmega8:

ADC_vect analog/digital converter

ANA_COMP_vect analog comparator

EE_RDY_vect eeprom ready

INT0_vect external interrupt 0

TIMER0_OVF_vect Timer0 overflow event

TIMER1_CAPT_vect Timer1 capture event

SPI_STC_vect serial transfer complete

USART_UDRE_vect USART data register empty

USART_RXC_vect USART receive complete

more AVR Peripheral Features

16 – bit Timer / Counter 1

● Two Independent Output Compare Units

● can be used as Pulse Width Modulator (PWM)

● Clear Timer on Compare Match (Auto Reload)

● One Input Capture Unit

● can be used asExternal Event Counter

● Four Independent Interrupt Sources

TOV1, OCF1A, OCF1B, and ICF1

16 – bit Timer / Counter 1


OCR1B and ICR1

are 16-bit registers

● write high byte first

read low byte first

(automatically done in C)

● clocking via prescaler or

external clock on pin T1

● output compare register

OCR1A/B can be used

for PWM generation

(output pin: OC1A/B)

or for interrupt request

16 – bit Timer / Counter 1

● Input capture Unit: timestamp external events on ICP1 pin (or on Analog comp.)

Can generate Input Capture Interrupt

16 – bit Timer / Counter 1

● Output Compare Units: compare TCNT1 with OCR1A and OCR1B

Can generate Output Capture Interrupt

● 13 PWM / Waveform

generation modes

● Top and Bottom values

● Auto reload

16 – bit Timer / Counter 1

● Mode configuration using TCCR1A and TCCR1B

PWM Mode, set/clear/toggle of OC1A/B, auto-reload, Noise canceller

Find Details in the ATmega8 datasheet !

16 – bit Timer / Counter 1

● Clock source configuration using TCCR1B

The UART Serial Interface

USART interface

●universal synchronous / asynchronous receiver / transmitter

●Full Duplex Operation: Receive and Transmit Registers

●Asynchronous or Synchronous Operation

● Frames with 5, 6, 7, 8, or 9 Databits and 1 or 2 Stop Bits

●Odd or Even Parity Generation and Parity Check

●Framing Error Detection, Noise Filtering

●Interrupts possible on TX Complete, TX Data Register Empty

and RX Complete

USART interface

●synchronous mode:

Pin XCK is used

as clock Input (slave)

or clock output (master)

●asynchronous mode:

receiver and transmitter

are clocked independently

USART interface

●Frame formats:

USART interface

●calculating the baud rate register value:

low and high byte of ubrr are written into the UBRRL and UBRRH registers

Accuracy depends on System clock source !

(see table in ATmega8 data sheet, pp 155)

USART interface

●Initialisation: set baud rate, frame format, enable TX and RX

RXC: RX complete

TXC: TX complete

UDR: Uart Data Register empty

FE: Frame Error

DOR: Data OverRun

PE: Parity Error

U2X: Double the USART speed

USART interface

●Initialisation: set baud rate, frame format, enable TX and RX

RXCIE: RX complete interrupt enable

TXCIE: TX complete interrupt enable

UDRIE: Uart Data Register empty interrupt enable

RXEN: Receiver Enable

TXEN: Transmitter Enable

UCSZ2: Character Size

RXB8, TXB8: Bit 8 for receive and transmit

USART interface

●Initialisation: set baud rate, frame format, enable TX and RX

URSEL: Register Select (1=UCSR/0=UBRRH)

UMSEL: 0=async. mode, 1=sync. Mode

UMP1, UMP0: Parity mode:

00 = disabled, 10 = even, 11=odd

USBS: Stop Bits: 0=1 Stop Bit, 1= 2 Stop bits

UCSZ2,1, 0 : character size

USART interface

character size selection using the UCSZ bits

USART interface

Selection of the baud rate using the UBRRH and UBRRL SFRs:

URSEL has to be 0 when writing to the UBRRH register

USART interface

●Initialisation: set baud rate, frame format, enable TX and RX

void USART_Init( unsigned int baud )


/* Set baud rate */

UBRRH = (unsigned char)(baud>>8);

UBRRL = (unsigned char)baud;

/* Set frame format: 8data, 2stop bit */

UCSRC = (1<<URSEL)|(1<<USBS)|(3<<UCSZ0);

/* Enable Receiver and Transmitter */

UCSRB = (1<<RXEN)|(1<<TXEN);


USART interface

●Sending bytes in polling mode

void USART_Transmit( unsigned char data )


/* Wait for empty transmit buffer */

while ( !( UCSRA & (1<<UDRE)) );

/* Put data into buffer, sends the data */

UDR = data;


USART interface

●Receiving bytes in polling mode

unsigned char USART_Receive( void )


/* Wait for data to be received */

while ( !(UCSRA & (1<<RXC)) ) ;

/* Get and return received data from buffer */

return UDR;


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