On Tue, 9 May 2000 14:38:25 -0400, you wrote:

> Any suggestions on an easier to interface add-on chip or type of PIC?

What I have done so I can use 16F84s in a master/slave serial bus is
to dedicate the INT pin on each slave to be the signal line. The
master pulls the line low for a few hundred microseconds (the time the
line is pulled low needs to be slightly greater than the length of the
longest interrupt on any slave).

The slaves all go into the ISR for the INT line, and watch the signal
line (polling). When it goes high, the master proceeds to clock out 8
bits, which is the slave address to send to. The slaves are all
syncronized, so they each receive the byte and compare it to their
slave ID. If it is the same, they do whatever is approriate in
communication with the master. If its not, they ignore everything else
on the data line and exit the ISR, not to be bothered again until the
signal line gets pulled low again. Only the master may pull the signal
line.

Very simple, very easy to do, very direct, and it works great. I
wouldn't pass huge amounts of data over this bus in one transaction,
since there is no clock pulse to do bit-synching with. But if all
you're doing is sending simple commands and receiving status info, it
works pretty well. The master can be connected to a MAX232 or whatever
to talk to the PC/Palm device.

Its certainly not a 100% efficient solution, but it is very simple to
implement, which for me is much more important...

Later,
Jon