Satel ETHM-1 - Manual (Page 23)

SATEL 2014-04-02
Appendix 4 - crc calculation example
Assume that the following data has to be send to INT-RS module: 0xE0, 0x12, 0x34, 0xFF, 0xFF (i.e. read information about user
with 1234 code). For this case the following frame should be generated:
0xFE 0xFE 0xE0 0x12 0x34 0xFF 0xFF 0x8A 0x9B 0xFE 0x0D
The 16-bit crc sum calculation goes as below:
1) crc := 0x147A
2) for byte b = 0xE0:
- crc := rl(crc) = rl(0x147A) = 0x28F4
- crc := crc xor 0xFFFF = 0x28F4 xor 0xFFFF = 0xD70B
- crc := crc + crc.high + b = 0xD70B + 0xD7 + 0xE0 = 0xD8C2
3) for byte b = 0x12:
- crc := rl(crc) = rl(0xD8C2) = 0xB185
- crc := crc xor 0xFFFF = 0xB185 xor 0xFFFF = 0x4E7A
- crc := crc + crc.high + b = 0x4E7A + 0x4E + 0x12 = 0x4EDA
4) for byte b = 0x34:
- crc := rl(crc) = rl(0x4EDA) = 0x9DB4
- crc := crc xor 0xFFFF = 0x9DB4 xor 0xFFFF = 0x624B
- crc := crc + crc.high + b = 0x624B + 0x62 + 0x34 = 0x62E1
5) for byte b = 0xFF:
- crc := rl(crc) = rl(0x62E1) = 0xC5C2
- crc := crc xor 0xFFFF = 0xC5C2 xor 0xFFFF = 0x3A3D
- crc := crc + crc.high + b = 0x3A3D + 0x3A + 0xFF = 0x3B76
6) for byte b = 0xFF:
- crc := rl(crc) = rl(0x3B76) = 0x76EC
- crc := crc xor 0xFFFF = 0x76EC xor 0xFFFF = 0x8913
- crc := crc + crc.high + b = 0x8913 + 0x89 + 0xFF = 0x8A9B
And the final crc sum is 0x8A9B.
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