~NOSPAM~phil@spam@ at @spam@advancedarchitecture.org
shares this code:
;Title 1khurts.asm
;a 1.00kHz square wave generator.
;program runs a xtal oscillator PIC16f872 to exactly 1000 hertz.
;comments: phil@advancedarchitecture.org
include "P16f872.inc" ; use definition file for 16F872
; configure the chip for a crystal oscillator, with code protection and watchdog timer off.
__CONFIG _CP_OFF & _XT_OSC &_WDT_OFF
; define RAM =, give RAM registers names.
CBLOCK 0x20 ; RAM starts at address 20h
d1
ENDC
;
org 0x0000 ; start address = 0000h
; INITIALISE PORTS
; binary used to see individual pin level
movlw b'00000000' ; all port pins = low
movwf PORTA
movlw b'00000000'
movwf PORTB
movlw b'00000000'
movwf PORTC
bsf STATUS,RP0 ; set RAM Page 1 for TRIS registers
; initialize ports
; set all pins to outputs, and analog pins to digital.
movlw b'00000000' ; all IO pins = outputs
movwf TRISA
movlw b'00000000'
movwf TRISB
movlw b'00000000'
movwf TRISC
movlw b'00000110' ; all analog pins = digital
movwf ADCON1
bcf STATUS,RP0 ; back to RAM page 0
; LED FLASH LOOP
Loop bsf PORTC,4 ; RC4 = high
nop ; these two nop's make each half of cycle the same delay.
nop
call Delay
bcf PORTC,4 ; RC4 = low
call Delay
goto Loop
; trial 1kHz delay subroutine
; delay is period/2
; 1kHz = 1000/s => period = .001 = 1ms
; 1ms/2 = 0.5 ms = .0005s
; 0.0005x1Mips = 500 instruction cycles (clock is 4MHz).
; 500 - 5 (overhead of calling delay, and looping) = 495
Delay movlw 0xA4 ;A4 = 164, see below, Delay is 2 instruction cycles so 495 - 2 = 493.
movwf d1
Count decfsz d1 ;493 required by Count, Count is 3 instructions each loop + 1 for skip, 492, w/o skip 492/3=164=A4
goto Count
return
END
