Scott Dattalo wrote:

 (Obsequious comments glossed over)

> Incidently, the TRIS instruction AFAIK is available on the f877 (at
> least it is in gpsim).  A quick glance at the data sheet shows that it
> isn't.

  Not so.  In fact, the opposite, but oh, so subtly.

  In all 14-bit series parts, TRIS and OPTION aren't confessed in the
instruction set tabulation, but appear with the bizarre petulant
"warnings" about the possibility of non-compatible vapourware in the
imagined future; in the detailed instruction descriptions.

  It gets worse!  I just browsed DS35007A-page 33 (PIC16F84A), which
contains the apocryphal: "Note: To maintain upward compatibility with
future PIC16CXXX products, do not use the OPTION and TRIS instructions."

  Since this document does *not* contain the full instruction
description, (refers rather to DS33023) it certainly doesn't help you to
understand TRIS and OPTION, *however*, and I have to laugh, because on
page 32 it contains the every-bit-as-sensible advice: "Note: Microchip
does not recommend code protecting windowed devices."

  I really think that says it all.

  To remain on track however (forever difficult), the PIC16F87X
datasheet DS30292A contains the admonishment about TRIS and OPTION,
which de facto *confirms* that they are there.  I really wonder why on
these parts they *didn't* remove that functionality.  Is it because they
actually wouldn't *dare* present a blatantly sub-functional part to an
ever more discerning market (notably: this list)?

  Presumably however they employed a knowledgeable proof-reader on this
occasion, as the comment about windowed devices has been edited out.

Tony Nixon wrote:

> I had 1 single pin floating out of 78 possible PIC pins (4 PICs) in
> the virtual car project and it caused the system to crash
> intermittantly.  Very hard to track down |:-(

  Oh, so *that's* how it happened!  :)

Alice Campbell wrote:

> hmm, good thought.  Now is there a nice way to terminate all
> those lines?

  My goodness, how soon these things are forgotten (overlooked)!

  Are we not discussing embedded *programming*? ;-)  Be a programmer;
terminate them in *software* (make them outputs, set them low, or port B
has pull-ups).
--
  Cheers,
        Paul B.