Hi all,

I intend to read a proprietary serial data stream from another product into
a spare PortA pin on a 16F pic.  Currently 8Mhz internal osc, but the PCB is
setup for a 3-pin resonator (20Mhz or other) resonator if necessary.

Essentially there is a relatively long idle period, followed by over 70
sequential data bits which are around 400ms long each, and at approx 1%
timing error from the sender.  This becomes fun because I don't have
interrupt-on-change on this pin, and trying to set a constant time for each
bit will be difficult because and error will accumulate over 70 bits.

So my plan is to generate Timer 2 interrupts every 50 to 100 ms looking for
the idle period, then end-of-idle transition, adjust the timer (PR2) to poll
in the middle as appropriate to capture the bit value, then adjust PR2 again
to end a few percent before the expected transition, and then poll in a loop
to accurately determine the edge/transition that marks the end of the bit
(the beginning of the bit).  The "few percent" will allow for all sources of
timing errors from the sender, receiver (pic) clock, etc.

Now the question -- since the pic is doing other things, the timer interrupt
that should be triggered a few percent before the end of the bit may get
delayed, so the few percent may change to 5 percent or more, and I could be
waiting for maybe over 100 clock cycles before returning from that
interrupt.  I hate doing that, and always try to keep my interrupt
processing as short as possible.  Is there another/better way to do this?

Cheers,
-Neil.

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