Syd said:
I am trying to learn PIC assember.
Can someone please give me the correct assembler code to program a
16F628A with all pins on PORTA and PORTB as outputs and then toggle
them Hi and Lo.
My efforts to date using MPLAB has always resulted in an error.
Here is some code that will toggle the output pins at quite a clip. IT IS
UNTESTED, but was cut from working code, so it should work fine. ;-) I
assume a 4MHz external crystal is connected. Watch out for line wraps from
the comments when you copy and paste this code.
;---------------------------------------------------------------------------------------------
; HEADER:
;---------------------------------------------------------------------------------------------
LIST P=16f628
RADIX DEC
INCLUDE "p16f628.inc"
__CONFIG _CP_OFF & _WDT_OFF & _XT_OSC & _PWRTE_ON &
_BODEN_OFF & _LVP_OFF
;---------------------------------------------------------------------------------------------
; EQUATES:
;---------------------------------------------------------------------------------------------
STARTOFRAM equ 0x20 ;First Usable RAM Location for
16f628
ENDOFRAM equ 0x6F ;Last Usable RAM Location for
16f628
FIXEDAREA equ 0x70 ;Start of shared memory
between banks
BANK2RAM equ 0xA0 ;Start of Bank 2 RAM
;---------------------------------------------------------------------------------------------
; General Purpose Temp Storage
;---------------------------------------------------------------------------------------------
cblock STARTOFRAM
LoopCounter
endc
;---------------------------------------------------------------------------------------------
; Common Area Temp Storage (visible from any bank)
;---------------------------------------------------------------------------------------------
cblock FIXEDAREA
;
; ISR Register Context Save Areas
;
INT_FLAGS
W_TEMP
STATUS_TEMP
FSR_TEMP
PCLATH_TEMP
endc
;---------------------------------------------------------------------------------------------
; START:
;---------------------------------------------------------------------------------------------
org 0x000
goto Start
; Interrupt handler
org 0x004
movwf W_TEMP ;Save everything
swapf STATUS, W
movwf STATUS_TEMP
movfw FSR
movwf FSR_TEMP
movfw PCLATH
movwf PCLATH_TEMP
goto IntExit
;
; Restore everything and return
;
IntExit
movfw PCLATH_TEMP
movwf PCLATH
movfw FSR_TEMP
movwf FSR
swapf STATUS_TEMP, W
movwf STATUS
swapf W_TEMP, F
swapf W_TEMP, W
retfie
;---------------------------------------------------------------------------------------------
;
; Main level code begins here
;
;---------------------------------------------------------------------------------------------
Start
bsf STATUS, RP0 ; Switch to Bank 1
movlw b'00000000' ; Define I/O on Port B (all
output)
movwf TRISB & 0x07F
movlw b'00000000' ; Define I/O on Port A (all
output)
movwf TRISA & 0x07F
bcf STATUS, RP0 ; Back to Bank 0
movlw 0x07 ; Turn off the comparators
(common newbie mistake to miss this)
movwf CMCON
clrf PORTA ; Drive all pins low
initially
clrf PORTB
Main
; Drive the pins high
movlw 0xFF
movwf PORTA
movwf PORTB
; A couple of no-ops to square up the output waveform
nop
nop
; Drive the pins low
movlw 0x00
movwf PORTA
movwf PORTB
; Loop back forever
goto Main
end ; Don't forget to include
one of these
