>
>
> decode using either an interrupt-on-change type of routine or something
> similar which doesn't take a lot of cycles on a fairly busy 'host'
> PIC.    The actual bitrate can be relatively low - even a few hundred
> bits/second should be fine.
>
> I've been looking around and other than async, it looks like manchester
> encoding might be an option, but I also wouldn't be surprised if i've
> missed something else.
>
> I'm asking this under the [PIC] tag as I am specifically hoping to find
> something which is PIC-processor friendly.
>


Lost somewhere in the sands of time was an interesting serial protocol used
on TI graphing calculators. There's plenty of good reference material on
Google, but it basically worked like this:
Two bidirectional lines with pull up resistors. The sender starts by pullin=
g
one line low, the receive end acknowledges by pulling the other line low.
They both release and start again. Zero's and ones were signified by which
line the sender pulled low.

Works _very_ well in a busy processor since every bit waits for an ack. Dat=
a
rate could be quite high with the addition of interrupts if so inclined.
Opto isolation may be more challenging, but seems workable.

I've always been surprised this hasn't found it's way into more
applications.

-Denny
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