Ken Parkyn <PICLIST@MITVMA.MIT.EDU> wrote:

> I have a problem using a 16C64.
>
> 00028 init    bsf     STATUS,5      ;go to bank 1
> 00029         movlw   0x3F
> 00030         movwf   TRISA   ;set port a as inputs
> ....
> 00034         bcf     STATUS,5      ;back to bank 0
> 00035         clrf    PORTA
>
> When I single-step it on MPSIM, at the instruction to clear PORTA,
> (00035) PORTA remains at 3F and the program steps on to the next
> instruction
>
> Is this an oddity of MPSIM, the 16c64 or me?

    It's you, Ken.  You've made PORTA all inputs; clearing the port
    output latches (which is what happens when you execute a "CLRF
    PORTA") won't affect what's read from the input pins, which is
    what MPSIM shows as the contents of the PORTA register.

    -Andy

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499