I have GENERALLY not run into trouble doing bsf and bcf on ports, but
I'm generally running light loads right next to the PIC.
        A shadow register is a location in RAM where you do all your bsf and bcf
operations for a particular port, then copy the register to the port.
        The 18c series PICs has separate access to the output latch on a port so
you can do bsf lata,0 and not worry about pin loading. In fact, the pin
can be shorted to ground and you'd still get what was previously written
to the latch. On the 18c, I use the port latch (lata, latb, etc.) for all
outputs (including bsf and bcf) and use the port registers (porta, portb,
etc.) for all inputs.

Harold


On Wed, 21 Feb 2001 13:31:37 -0500 Drew Vassallo <snurple@HOTMAIL.COM>
writes:
> >Is this a known problem with PICS?
>
> Yes.  Consecutive PORT operations (namely bcf/bsf) do not always
> work with
> higher capacitance loads.  Also, there is a warning on consecutive
> PORT
> write/read operations in many of the datasheets.  It's always a good
> idea to
> add a nop (or even more than 1) between these commands.
>
> >What do you mean shadow reg?
>
> I dunno.  Never used them.  I would be interested, though, because I
> have
> some untested 20MHz I^2C code that I need to use in the future.  If
> there's
> going to be a problem, it would be nice to know it.
>
> --Andrew
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