Tait T2000-A75, Operation Manual, Page: 18 / 38

18 M2256-000-00-051 November 2001
Calculating the [CHECKSUM]
[CHECKSUM] is calculated by applying the following algorithm:
1. Take the modulo-2 sum of all message bytes preceding [CHECKSUM].
2. Retain bits 0 to 7, discarding any higher order bits resulting from the summation.
3. Form the two’s complement of the remainder.
4. Convert the binary number into two ASCII-hex digits, MSD first.
Example
#12C401060A010000BASE8F
1. Take the modulo-2 sum of all message bytes preceding [CHECKSUM].
• # = 23h, 1 = 31h, 2 = 32h, C = 43h etc. therefore the modulo-2 sum is:
23h + 31h + 32h + 43h + 34h + 30h + 31h + 30h + 36h + 30h + 41h + 30h + 31h + 30h
+30h + 30h + 30h + 42h + 41h + 53h + 45h = 471h
2. Retain bits 0 to 7, discarding any higher order bits resulting from the summation.
• 71h
3. Form the two’s complement of the remainder.
• 71h = 0111 0001
two’s complement = 1000 1111
4. Convert the binary number into two ASCII-hex digits, MSD first.
• 1000 1111 = 8F