Correct way to program ports on 16F628A - Help

If it were the 16F88, I'd be able to help, because that's what I have. Either way, it seems as if the following might be a lead to what you want (one of the programs does exactly what you asked for):

Don't fear the Google. PSM

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

;--------------------------------------------------------------------------------------------- ; 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