I wrote: UART ;-)

David Tait wrote:
> about the only non-MPU interface UART around these days is the 40-pin
> 6402.  Like all UARTs it needs a clock generator; and it also needs a bit
> of glue logic to play the games I want it to.

I hope I'm not conflating two threads here: the serial port driven
programmer and the PIC expander.  I would not suggest a UART for the
latter, where you can use a data pin and clock pin and shift the bits out
in any format you want.  But for the general case of a serial port, you
may not have any extra pins to play with and you may not have close
control over the character timing.

If you really want to build a programmer that can be used on a generic
serial port with pins 2, 3, and 7, like say on a UNIX box, I think it has
to have a baud rate generator, the functionality of a UART, and plenty of
glue.  I would be delighted to learn that's not true.

William Chops Westfield wrote:
> Creating a port capable of doing this in a general fashion, while
> maintaining the ability to control timing of the bit-twiddling to a very
> fine degree (which is probably why the parallel port was used in the first
> place) is going to be a difficult task.

Yep.  I would expect that things like the timing of a program pulse would
have to be done with a one-shot or something.  And you might still need
the CMOS shift register on the UART outputs to expand to the number of
bits you need.  And yes, a non-MPU-buss UART is probably 40 pins.

Maybe this is all much more complicated than what you wanted to build.
If so, chalk it up to the ramblings of a software weenie.  BTW, I'm
perfectly happy with bit twiddling on a PC parallel port; it's just the
opposite of "universal" though.