>Reconsidering, I will abandon the USART.  I am going to use the open drain
of
>RA4 (16F628) for the TX and an ordinary input for RX.  All I need to send
>between the PICs is three bytes, a control byte, a security byte and maybe
a

I fear you are cutting off your nose to spite your face.

Use an external transistor on the TX pin of the uart to give yourself the
open drain equivalent - saves having to generate/debug a software uart
transmitter (assuming you are still going to use the hardware uart to
receive. hardware cost is one transistor and two resistors, less the
resistors if you use one of those so-called digital transistors that have
the resistors built in.

Then on your master PIC you will just need an inverter with a pull up
resistor on the input. This could also be a single transistor if you select
the resistor values right.

It would pay to have a similar arrangement on the transmit from the master
to the slave devices as well, mainly to keep noise spikes from destroying
your PIC's, you are likely to have enough problems with spikes mashing your
messages without worrying about destroyed chips as well.

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