> My problems are on the preamble, sync word, and the checksum/
> CRC. Basically, it's packet transmission and reception.

Preamble's are just a long string of 1's and 0's to indicate transmission is
about to start.

Sync words are just a collecting of 1's and 0's in a specific pattern that
is long enough for the receiving system to lock onto (correlate) and
synchronise at the appropriate bit rate.

Checksum is a Cyclic Redundancy Check and is normally a delay line with
XOR'ed taps fedback into the delay line input. (The feedback bit gives you
the "cyclic" term)

There are many many text books that explain CRC generation. It can be as big
or small as you like. If it's a PC you are talking to then I don't know the
correct polynomial for the CRC in this circumstance.

You notice how again you can break this down into smaller and smaller bits.
If it's a PC you're talking to get the speification of the interface and
read it. Then just try a simple terminal program and turn off all fancy
handshaking or parity checking. Just try raw data communications. When that
works try adding CRC (parity) etc etc.

Pete

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