A quick peek at the datasheet (hint, hint) reveals that PORTA has a dual
duty with analog comparators.  I don't see any disabling code for those in
your code...that's almost certainly the problem:  the PORTA pins need to
be configured as digital pins.

The following code should disable the comparator:

movlw  b'00000111'  ; the lower 3 bits of CMCON control the status of
                              ; the compartor
movwf CMCON

CMCON is in bank 1, so no selection needs to be done.  Alles klar?

Mike H.


>From: rrc124+@PITT.EDU
>Reply-To: pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>
>To: PICLIST@MITVMA.MIT.EDU
>Subject: [PIC]:beginner needs help with input pins, read all the FAQ
>Date: Tue, 10 Jun 2003 20:47:34 -0400
>
>I can't get my inputs to work. I am using a pull up switch, have set all
>pins but 1 to outputs, then tied them to ground. I am using a PIC16F628
>with the configs set to everything off/disabled except the power up timer.
>I have selected the internal oscillator. I'm a programmer..not EE, so
>that's my weak point but i have been checking the circuit for 3 days and
>can't find what's wrong. The chip works because i got one of those LED
>blinking things to work fine. Guys...thank you so much...it's very
>upsetting when you're just starting out and can't get the easiest thing to
>work. The only odd thing i could find was that my programming software
>(WinPicProg, from Dontronics) generates a different config word then does
>MPLAB with the same settings.
>
>Here is my code:
>
>TMR0            EQU             1
>OPTION_R        EQU             1
>PORTA           EQU             5
>PORTB           EQU             6
>TRISA           EQU             5
>TRISB           EQU             6
>STATUS          EQU             3
>ZEROBIT         EQU             2
>CARRY           EQU             0
>PCON            EQU             0EH
>COUNT           EQU             20H
>
>                         LIST P=16F628
>            ;  tells which processor is use
>;MPLAB generated        __CONFIG 0x3F10
>                         __CONFIG 0x3D10  ;WinPicProg generated
>
>                         org             0
>                         goto    START
>
>; config section
>
>START                   bsf     STATUS, 5
>                         movlw   b'11111111'
>                         movwf   TRISA
>                         movlw   b'00000000'
>                         movwf   TRISB
>
>                         movlw   b'00000100'
>                         movwf   OPTION_R
>                         clrf    PCON
>
>                         bcf     STATUS, 5
>                         clrf    PORTA
>                         clrf    PORTB
>
>; program starts now
>
>BEGIN           btfsc   PORTA, 1
>                         goto    BEGIN
>                         movlw   b'11111111'
>                         movwf   PORTB
>KEEPON          btfss   PORTA, 1
>                         goto    KEEPON
>                         clrf    PORTB
>                         goto    BEGIN
>
>                         END
>
>Here is my circuit:
>                                    GND
>                                     |
>[9V+ Battery]--[914 diode]--[7805 Volt Reg]--+
>                                              |
>                           +-----[10k Res]----+
>                           |                  |
>             A1/PIN 18-----+--[switch]--GND   |
>                                              |
>            Vdd/PIN 14------------------------+
>
>            Vss/PIN 05------------------------GND
>
>             B4/PIN 10--[470 Ohm Res]--[LED]--GND
>
>             B3/PIN 09--[470 Ohm Res]--[LED]--GND
>
>All other pins set as output, tied to ground. The switch part of the
>circuit allows 4.5V to A1 and when pressed drops the voltage down to 0. I
>checked with my multimeter. Thank you so much everyone.
>
>E-Mail: rrc124@pitt.edu
>
>Robert Campbell
>
>
>--
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