; CE-2800 ConditionalLoop.asm
; Purpose: Demonstrate the use of conditional branching to control looping (iteration)

.NOLIST
.INCLUDE "m32def.inc"			; contains .EQU's for DDRB, PORTB, and a lot more
.LIST

.CSEG							; this means further directives are for the Code Segment
.ORG 0x0
	rjmp start					; initialize Reset Vector

.EQU start = 0x2a				; define a symbol to represent address 0x2a in program memory
.ORG start						; define the beginning of the program - where the Assembler places further program instructions

; Note: choice of registers below is somewhat arbitrary
.DEF sum = R20					; define an alias for R20 named "sum"	
.DEF one = R21					; another alias 
.DEF temp = R22

	ldi			temp, 0xff		; load 0xff into temp register
	out			DDRB, temp		; tell DDRB to configure pins as output or input (0xff means all output)

	ldi			sum, 0xf5 		; initialize R20 (via alias)
	ldi			one, 1			; initialize R21 (via alias) to 1

; Note: "loop:" is a label representing an address in program memory.
; The value of loop: is automatically determined by the Assembler
loop:
	add			sum, one		; add value in register one to register sum
; SREG is modified by ALU after each operation
; During add, the Z flag is set only if the result is 0
; In this loop, the result will be 0 when sum "rolls over" from 255 (0xff) to 0
	brne		loop			; if NOT zero, keep summing

done:							; we get here after sum rolls over to 0
	rjmp		done			; loop forever

;	jmp			done			; we can use this instruction in place of rjump,
								;  but it takes 2 words of program memory
								;  instead of 1, and twice as long to execute