Hello Christopher

Have a look at the data sheet at the I/O port part. Some of the porta pins
have additional features assigned to it as the default, and you must change
that so that it is configured as io ports and not something else. E.g. you
should move a value of 7 (b'111') to the cmcon register to deactivate all
the comparitors, and enable the io pins.

Hope this will help

Regards,

Mias van Vuuren



-----Original Message-----
From: Christopher Tyler [mailto:holochris_za@YAHOO.CO.UK]
Sent: Monday, September 10, 2001 10:53
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]:16F628 from 16F84

Hi all
I am working on a project that was using the 16F84. On this chip, the
program runs perfectly. But we are trying to cut our costs. Someone
suggested we use the 16F628 instead. I had a look at the data sheets on
the 16C628, and they seem mostly the same. So I moved to the new
chip. But now the program doesnt work anymore.
The problem is when simulating using MPLAB. U can't change the state of
any of the  "pins" on PORTA. I have tried using Pin Stimulis Files,
Asynchronis Stimulis, etc. But none of the pins ever go high. Port B
works
fine. Does anyone know what I could be doing wrong? We havent used the
628 before....are there any issues to watch out for? (Like the fact that
the General purpose data memory starts at 20h instead of 0Ch on the
16C84)

We had similar (unsovled) problems when we tried to change the code to
work on a 12C508. GPIO,4 would not go high. Could it be something to do
with weak-pull ups or whatever? :)

Here is what the code looks like that sets up the ports,etc. Maybe that
will
help?
#include  P16F628.inc
LIST   P=PIC16F628

PORTASETUP     EQU B'00000011'
PORTBSETUP     EQU B'00001111'
STATUS               EQU H'03'
FLAG1                 EQU H'20'
TIME1                  EQU H'21'
DELAY                EQU H'22'
DELAY2              EQU H'23'
DELAY3              EQU H'24'
DIP                       EQU H'25'
TMOUT               EQU H'26'
SERVFLG            EQU H'27'
LED1FLG            EQU H'28'
LED2FLG            EQU H'29'
LED3FLG            EQU H'2A'
LED4FLG            EQU H'2B'
LEDSTAT            EQU H'2C'

                            org H'01'
START                bsf             STATUS,5
                            movlw        PORTASETUP
                            movwf        h'85'
                            movlw        PORTBSETUP
                            movwf        h'86'
                            movlw         b'00000111'
                            movwf        81h  ;OPTION register
                            bcf             STATUS,5
                            clrf             PORTA
                            clrf             PORTB
                            clrf             LEDSTAT    ;
                            goto           MAIN

Thanks for help in advance..... :)
Christopher Tyler

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