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I am trying to figure out how the calculate the CRC for very simple SDLC frames.

Using an MLT I am capturing the stream and i see some simple frames being sent out like: 0x3073F9E3 and 0x3011EDE3

From my understanding the F9E3 and EDE3 are the 2 byte checksums of the 3073 and 3011 since that is all that was in that frame.

using numerous CRC calculators and calculations I have been able to get the first byte of the checksum, but not the last byte (the F9 and the ED).

Using this calculator (http://www.zorc.breitbandkatze.de/crc.html):

  1. Select CRC-CCITT
  2. Change Final XOR Value to: FFFF
  3. Check Reverse Data Bytes and reverse CRC result before Final XOR
  4. Then type the input: %30%11

Which will give the output B8ED so the last byte is the ED.

Any ideas?

dsolimano
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cuatro
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1 Answers1

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You are getting the correct crc16's (F9 F8, ED B8). I don't know why your last byte is E3 in both cases. This is perhaps a clue that the packets are not being disassembled correctly.

Mark Adler
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