Charles Craft wrote:

> I think the spec sheet at Xilinx showed a JTAG port.
>
> Wouldn't that be used for programming the part?
> Aren't JTAG interface kits pretty easy to build or inexpensive to purchase?

Actualy, I was think about this while driving the kids
to school this morning...

(Note, I haven't studied the JTAG protocol, but it's two pins,
one "clock" and one "data", right ?)

Why not connect the JTAG pins of the CPLD to two unused (or, if
no unused pins, maybe share pins with something else) of the
PIC. Then a function in the PIC firmware could do the re-programming
of the CPLD from the PC-app. (Is there some high voltage needed
for programming ? Then perhaps a pin-header could be added for an
extenal Vpp to the CPLD ?)

Note that all that have to be done now, is to create the connections
on the PCB, the support in firmware and in the PC-app could be added
later so we don't slow down the whole thing.

In this was, the "hardware" could be adjusted/modifyed on-the-fly.
Thsi would have been much harder with discret 74-type logic :-)

Jan-Erik.

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