David VanHorn <PICLIST@MITVMA.MIT.EDU> wrote:

> I'd like to see the ability to breakpoint on modification of a
> location

    David:

    The PIC-Master doesn't support that, but the upcoming MPLAB-ICE
    emulator will.

> Can an 84 expert tell me, what the PCLATH is good for on the '84?
> It seemed to get in my way a bit, and looking at it, it didn't seem
> to perform a useful function. My assumption is that it's an
> "appendix" left over from some other flavour of device that has more
> ram or something.

    On the 16x84, PCLATH isn't necessary for CALLs and GOTOs, since
    the entire destination address will fit in the CALL or GOTO
    opcode.

    It IS, however, useful when you're doing a computed GOTO (e.g.,
    for a table lookup) where you modify PCL directly.  Since the
    result of an operation on PCL (like, say, "MOVLW 3 / ADDWF PCL")
    is only 8 bits wide, PCLATH must be preset if your
    PCL-modification will cross a page boundary or whatever.

    Details are in the Microchip appnote that deals with table
    lookups (sorry, don't remember the number), and somewhere in the
    "Answers" section of the Fast Forward Engineering web page at:

        http://www.netcom.com/~fastfwd

    -Andy

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499 (personal)
=== http://www.netcom.com/~fastfwd (business)