I was dissapointed to find that the picstart programmer was incapable of
programming the data memory on a 16c84. (or at least so I'm told by my
microchip rep.)

As I have not yet seen a serial mode programmer designed for the mac I
had an Idea that may work in hardware.

Looking at the programming spec in the databook, all that appears to be
different between programming "programme". and data memory is the need
to set RB0 to 1 during the control word.
I assume that if that is done the picstart and mps16b software will
think it is programming prog memory while it is actually reading/writing
from the data memory. I'm not quite sure what happens when it tries to
write/read addresses above 40h but lets not worry about that just yet.

I believe that a simple circuit;

RB7 ->[inverted] ->
                    [AND]-> [DIODE]-> RB0
RB2 ->[XOR]------->
RB3 ->[   ]

would give the logic required, that is RBO forced to one when a "load
data" or "read data" instruction is sent to the chip. At all other times
I assume the diode woold look like a high impedence to 0, and not effect
the programmer to chip traffic.

Before I try this and blow everything up, I invite comments.

a) good idea, might work.
b) good idea, will not work.
c) why bother when there is a much better way of doing it.(remember this
needs to work on a mac, and I do not want to buy a more expensive
programmer!)
All feedback in these catagories appreciated.
(As I have not tried it out, please do not destroy your own picstarts.)


john