Switches and LEDs - An Atmel ATmega328 Program

main.asm

;Equate easy to read names to the I/O memory addresses
.EQU DDRB = 0x04
.EQU PORTB = 0x05

.EQU PIND = 0x09
.EQU DDRD = 0x0A
.EQU PORTD = 0x0B

.CSEG
.ORG 0x0200
	;setup bits 2 and 3 of port D as inputs
	IN R16, DDRD
	ANDI R16, 0b11110011
	OUT DDRD, R16

	;setup bits 0 and 1 of port B as outputs
	IN R16, DDRB
	ORI R16, 0b00000011
	OUT DDRB, R16

	;both pins B0 (D8) and B1 (D9) start low
	IN	R16, PORTB
        ANDI R16, 0b11111100
        OUT PORTB, R16

	;Enable the pull up resistor for bits 2 and 3 of port D
	IN	R16, PORTD
        ORI	R16, 0b00001100
        OUT PORTD, R16

LOOP:
	IN R16, PIND
	ANDI R16, 0b00000100
	LDI R17, 0x00
	CP R16, R17
	BREQ LED1

	IN R16, PIND
	ANDI R16, 0b00001000
	LDI R17, 0x00
	CP R16, R17
	BREQ LED2

	IN R16, PORTB
	ANDI R16, 0b11111100
	OUT PORTB, R16
	RJMP LOOP

LED1:
	IN R16, PORTB
	ORI R16, 0b00000001
	OUT PORTB, R16
	RJMP LOOP

LED2:
	IN R16, PORTB
	ORI R16, 0b00000010
	OUT PORTB, R16
	RJMP LOOP

.EXIT