Paja

Digital and analog pins are controlled by accessing bits. Arduino NG Diecimila has Atmel Atmega8 on board and Atmega8 has two digital ports and one analog (digital to analog converter) port. This post describes Pin assign between Arduion and Atmega8. It also describes location of bits assigned to specific ports.

With AVR-GCC, digital pins need to be declare if they are output or input mode before pins create any signal.

 

#include <avr/io.h>

#include <util/delay.h> 

int main(void){

DDRB = (1<<PB5); // make Arduino Pin 13 (Atmega8 PortB pin 5) an output

for(;;){

char i;

for(i = 0; i < 10; i++){

_delay_ms(30);      // max is 262.14 ms / F_CPU in MHz

}

PORTB = (1<<PB5);     // Put Arduino Pin 13 (Atmega8 PortB pin 5) HIGH

}

return 0;

}

 

 

Pin assign in Arduion NG and Atmega8

Arduino Pin	0 (RX)	1 (TX)	2	3	4	5	6	7	8	9 (PWM)	10 (PWM)	11 (PWM)	12	13
Atmega8 Pin (Port + Pin)	PD0	PD1	PD2	PD3	PD4	PD5	PD6	PD7	PB0	PB1	PB2	PB3	PB4	PB5

Atmega8 has Port B and D as digital I/O. Port C is for digital to analog converter. 

Arduino NG schematic

 

DDRB Direction pin register (0 -> input, 1 -> output)

Bit	7	6	5	4	3	2	1	0
	—–	—–	DDB5	DDB4	DDB3	DDB2	DDB1	DDB0
Arduino Digital Pin			13	12	11	10	9	8
Read/Write	R	R	R/W	R/W	R/W	R/W	R/W	R/W
Initial value	0	0	0	0	0	0	0	0

DDRD Direction pin register (0 -> input, 1 -> output)

Bit	7	6	5	4	3	2	1	0
	DDD7	DDD6	DDD5	DDD4	DDD3	DDD2	DDD1	DDD0
Arduino Digital Pin	7	6	5	4	3	2	1	0
Read/Write	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Initial value	0	0	0	0	0	0	0	0

If DDxn is written logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input pin.

 

 

PORTB register (Digital I/O)

Bit	7	6	5	4	3	2	1	0
	—–	—–	PORTB5	PORTB4	PORTB3	PORTB2	PORTB1	PORTB0
Arduino Digital Pin			13	12	11	10	9	8
Read/Write	R	R	R/W	R/W	R/W	R/W	R/W	R/W
Initial value	0	0	0	0	0	0	0	0

PORTD register (Digital I/O)

Bit	7	6	5	4	3	2	1	0
	PORTD7	PORTD6	PORTD5	PORTD4	PORTD3	PORTD2	PORTD1	PORTD0
Arduino Digital Pin	7	6	5	4	3	2	1(TX)	0(RX)
Read/Write	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Initial value	0	0	0	0	0	0	0	0

If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one).

 

 

PINB register (Digital In)

Bit	7	6	5	4	3	2	1	0
	PINB7	PINB6	PINB5	PINB4	PINB3	PINB2	PINB1	PINB0
Arduino Digital Pin	7	6	5	4	3	2	1(TX)	0(RX)
Read/Write	R	R	R	R	R	R	R	R
Initial value	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A

PIND register (Digital In)

Bit	7	6	5	4	3	2	1	0
	?	?	PIND5	PIND4	PIND3	PIND2	PIND1	PIND0
Arduino Digital Pin			13	12	11	10	9	8
Read/Write	?	?	R	R	R	R	R	R
Initial value	?	?	N/A	N/A	N/A	N/A	N/A	N/A

These ports are used to read pin status.