----- Original Message -----
From: Bob Barr <bob_barr@HOTMAIL.COM>

> Useful perhaps, but IMHO very dangerous to use.
>
> An undocumented opcode in a processor is generally a side-effect that was
> never intended to be there in the first place. The original chip
> manufacturer (or a licensed second source) is under no obligation to keep
> that side-effect present in future versions of the chip.

This is pretty much the reason not to use them.  Even if there were valid
opcodes intentionally put in, it might be under a specific revision,
specific sub-family, specific part, etc., it may be removed at any time and
might further reduce the range of chips that your code would work under.

Microchip is trying to ween developers from using OPTION and TRIS for the
16x family as it is, if those are possibly subject to future elimination or
non-support on new chips, I imagine the undocumented ones way be under an
even greater threat.

Jeff

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu