Output number when button is pressed

This is simple demo program of reading button state, lighting LEDs, sending information via USART. 8 buttons are connected to Atmega16 port A, 8 LEDs to port B via current limiting resistors. While none of buttons arent pressed there is running light on LEDs performed, but when any of buttons is pressed then LEDs display current 8 buit counter value in binary format. Same value is sent via USART – you can see number in terminal if connected.

The program is very simple:

#include <avr/io.h>

#include <util/delay.h>

#include <stdio.h>

#ifndef F_CPU

#define F_CPU 1000000

#endif

//set desired baud rate

#define BAUDRATE 9600

//calculate UBRR value

#define UBRRVAL ((F_CPU/(BAUDRATE*16UL))-1)

char n,		//number

	 c;		//current state of display

int main(void)

{

	//Set baud rate

	UBRRL=UBRRVAL;		//low byte

	UBRRH=(UBRRVAL>>8);	//high byte

//Set data frame format: asynchronous mode,no parity, 1 stop bit, 8 bit size

	UCSRC=(1<<URSEL)|(0<<UMSEL)|(0<<UPM1)|(0<<UPM0)|

	(0<<USBS)|(0<<UCSZ2)|(1<<UCSZ1)|(1<<UCSZ0);	

//Enable Transmitter and Receiver

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

	DDRA=0x00;	//all A port pins as input

	PORTA=0xFF;	//Enable internal Pull-Up resistors

	DDRB=0xFF;	//All B port pins as output

	while(1)

		{

			c=1; 	//start with first LED

			while(PINA==0xFF) //wait for button to be pressed

				{

					if (c==0) c=1;	//if light passed all leds start over

					PORTB=~c;		//LED on

					_delay_ms(100);//short delay

					n++;			//increase number value

					c=c<<1;			//shift li9ghted LED

				}

			//wait for empty transmit buffer

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

			UDR=n;		//send number to USART

			PORTB=~n;				//and dislpaly number with led(binary)

			_delay_ms(200);	//long delay

			PORTB=0xFF;			//All LEDs OFF

		}

return 0;

}

You can compile it with AVRStudio4. If you want to simulate the circuit by yourself, you can download Proteus design file . The only limitation is that Atmega16 model doesn't support USART (only UART), so no terminal modeling is present.