Rob
Thanks for the information.I am using a picstart plus from microchip to
program my chip. My friend, a local engineer came up with this idea and i
implemented his idea and ran into this problem. He keeps telling its my part
this is causing this problem. But  I modify the program to run in an F 84
and it did the same thing. . The idea about the pass counter was to make
sure that all the leds would come on and they do. This was old idea that i
had some years back
thanks again
Mike Johnston
----- Original Message -----
From: "Rob Stockley" <robstockley@MOWGLI.NET.NZ>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, January 13, 2004 10:27 PM
Subject: Re: [PIC:] 16c54 scanner


> Michael,
>
> Let me try to explain what is going wrong by rewriting the comments in
> your code. I have not changed or removed any commands, just the
> comments.
>
> pascnt1
>         movlw   0x05
>         movwf   C1              ;counter contains value 5
>
> setbitaf
>         clrf    PORTB           ;portb leds all off
>         bsf     PORTA,0         ;first led of porta is lit
> pointaf
>         decf    C1,f            ;decrease counter by one
>         call    delay           ;wait a bit
>         bcf     STATUS,C
>         rlf     PORTA,same      ;change to the next led in porta
>         btfsc   PORTA,3         ;if the fourth led is lit
>         goto    pascnt2         ;time to switch ports
>                                 ;but hang on we only just lit the
>                                 ;fourth led. Don't we need to wait
>                                 ;a bit?
>         movf    C1,f            ;when PORTA,3 is lit, C1=2 so Z will
>                                 ;never be set by this command
>         btfss   STATUS,Z        ;Z is never set so we always execute
>                                 ;the next instruction
>         goto    pointaf         ;keep processing porta
> pascnt2
>         movlw   0x09            ;switching to portb so
>         movwf   C1              ;load counter with 9
> setbitbf
>         clrf    PORTA           ;turn all porta off
>                                 ;remember this is only 5 instructions
>                                 ;since we turned it on!!
>         bsf     PORTB,0         ;turn on portb's first led
> ..........etc
>
> Do you see how your delays are misplaced? A simple fix would be to
> insert another "call delay" immediately after pascnt2. You'll need to
> modify your reverse routines in a similar way.
>
> Also, to tidy up your code, ask yourself these questions;
>
>         What does the counter do?
>         What does checking PORTA,3 do?
>
> If the answers to these are the same then you most likely only need one
> of them.
>
>         When will the Z flag be set?
>         Can this ever happen?
>
> I hope all this is helpful. PICs are great fun to work with. Out of
> interest, what are you using to program them?
>
> Rob
>
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