> >> 1) How few pins can I get away with?
> >
> >    For example:
> >
> >    Your Master PIC controls the Slave PIC's MCLR line.  The Master
> >    normally keeps the Slave's MCLR line high (out of reset).  When
> >    the Master wants to send a message, it pulls the Slave's MCLR
> >    line low, then pulls it high for a short time before pulling it
> >    low, then high again.
> >
> >    The "message" is the time between MCLR-low pulses.
>
> OK, that's got me interested.. the SLAVE's second job out of reset is to
> increment a register, so that next time it comes out of reset, the first
> job it has is testing that same register for the message sent to it... So
> far so good. What's the approved method of determining if it's a valid
> message, or just random powerup garbage?

This method sounds dangerously exciting. I guess, glitches and
power up garbage can be filtered by the value of timer.
That is data only valid if the timer is between N1 and N2.

Aydin

> Bob