Hi,

I am hoping to not to have to totally re-invent the wheel.  I am looking
for a way to set up a bi directional RS-422/485 interface for PC's.

The protocol is propietary, and the signalling rate is something like 10000
BPS.  I am only looking for straight translations of 8 bit numbers, and a
little bit of one byte header de/encoding. I beleive I am guaranteed a
couple ms between each 6 byte burst of data.  Any ideas?

What is the easiest way to do this?  Dropped characters are unacceptable.
I was thinking a ISA interface, but if I use the PIC16F84 as I'd like, it
would only have 10 lines free after doing the RS-422/485 interface.  Is
that enough to handle a bi-directional protocol?  Is the Parallel port an
option?  maybe a nibble at a time?  Or could the PIC keep up spitting out
to the serial port at like 33600 or so and decoding the data?

I need simple yet fast communications to and from the PIC chip.  I need at
least an outgoing buffer of at least 12 to 18 bytes, and maybe an incoming
buffer if needed.  Depending on how much time it takes to load or read data
to and from the PIC.

Any hardware or software ideas, solutions, or examples are appreciated.
David
skipper@interlog.com