pic microcontroller discussion list <> wrote on Thursday, March 13, 2003
10:22 AM:

>    I'm wondering if a single pin of portD can be
> toggle input or output by using BCF,
>    e.g
>        BCF  TRISD,7 ; to set bit 7 of portD as output
>
>  The above don't seem to work.
>
>  However, if i use:
>        MOVLW 7FH
>        MOVWF TRISD
>
>  I measure and confirmed that pin 7 of portD goes low.
>

Check your bank bits, if necessary for your processor.  If it's not an 18F,
you will need something like

>    Initialization: MOVLW  00H
>                    MOVWF  PORTD
                                bsf STATUS,RP0  ; bank 1 for TRISx registers
>                    MOVLW  FFH
>                    MOVWF  80H^TRISD ;set all input
                                bcf STATUS,RP0  ; bank 0 for normal operation

However, the real problem is probably that when you change the port to an
output, it's initial value will be what it's just read on its input.  Try
adding clrf PORTD after you have change the tristate, to clear any output
pins.

Apart from that, I can't think why there might be a difference between your
bcf and movlw approaches, if those are the only changes to the code.

Nigel

--
Nigel Orr, Design Engineer                 nigel@axoninstruments.co.uk
Axon Instruments Ltd., Wardes Road,Inverurie,Aberdeenshire,UK,AB51 3TT
               Tel:+44 1467 622332 Fax:+44 1467 625235
                   http://www.axoninstruments.co.uk

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