On Sep 4, 1997, John Craft asked...

> If this is infantile, excuse me, but on the PIC 14000
> can I make the entire PORTD a general output.
> I have set the TRISD, and tried to set the options
> to turn off I2C and AD functions with no luck.
>
> It's as if it toggles.  I turn on bit 0, then 1 and 0 goes off.
>
> Any thoughts.  The 14000 is nice, but way too many options.
>

I had a very similar problem last week using Port C on the
PIC 14000 for INPUT.  I would provide an external high input
on one of the lines, and sure enough, when I read Port C,
the corresponding bit was set.  Then, if I provided an
external high input on one of the other lines, it would
set the proper bit, but the other bit turned back off.

Needless to say, the problem was quite perplexing.  I finally
got it to work by doing the following:

Prior to configuring Port C for input, I would first configure
it for output.  Then I wrote 0FFh to the port to set all of
the output lines high.  Then, I switched the port back over
to input (using TRISC).  From that point on, there were no
more vanishing bits.  Why this works is beyond me.

I realize that your question was about using Port D for
OUTPUT, but the problems you are having seemed similar enough
to warrant a posting.

As far as the 14000 having too many options, they did indeed
pack a lot into this particular chip, except much needed
program memory.  With only 4K of program space, its a challenge
to make use of all of the chips options in a single application.
I wish they would make an 8K version of this chip.



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