Hi.  I have a SilentRadio ADT7405 LED Sign that can be serially =
programmed using an old DOS program.  I want to be able to program it =
using a PIC and/or my own software on the PC.  My problem is there seems =
to be some sort of CRC check in the serial protocol that I can't figure =
out.  I have sent messages from the DOS program and used another PC to =
catch the serial output.  Here's an example of a message that says the =
letter "A"

00 00 00 00 00 00 00 FF 35 35 00 0B 5A BA 01 00 00 05 00 17 02 41 1F E9 =
1D

the 00 00 00 00 00 00 00 FF 35 35 00 part is always the same for all =
messages I think.  01 00 00 05 00 17 02 have to do with Odd/even stuff =
and message length.  41 is the ASCII "A".  1F is also related to length. =
 now the E9 1D is the hard part.  I believe it is a CRC check of some =
kind but I can't figure it out.  Is there anybody out there who thinks =
they may be able to help me out?  I've been searching for an answer to =
this problem for a very long time.  If you think you might be able to =
help out, I will be glad to provide more examples and if you like I can =
send you the DOS program if that would help. =20
Thanks for any help or tips!

   -Dan

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