; **************************************************************
; * R/2R-Network produces a triangle signal on Port D          *
; * (C)2005 by info@avr-asm-tutorial.net                       *
; **************************************************************
;
.INCLUDE "8515def.inc"
;
; Register definitions
;
.DEF rmp = R16 ; Multipurpose register
.DEF rdl = R17 ; Delay counter
;
; Constants
;
.EQU maxAmp = 127 ; Maximum amplitude setting
.EQU delay = 1 ; Delay, higher value causes lower frequency
;
; Main program start
;
	ldi rmp,0xFF;  Set all pins of Port D as output
	out DDRD,rmp
triangle:
	clr rmp
loopup:
	out PORTD,rmp ; to port
	ldi rdl,delay
delayup:
	dec rdl
	brne delayup
	inc rmp ; next higher value
	cpi rmp,maxAmp
	brcs loopup
loopdwn:
	out PORTD,rmp
	ldi rdl,delay
delaydwn:
	dec rdl
	brne delaydwn
	dec rmp
	brne loopdwn
	rjmp triangle ; and again forever