Spellman uX SERIES, Инструкция по эксплуатации

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118153-001 Rev. B
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The following is sample code, written in C#, for the generation of checksums:
for ( int n = begin; n < end; n++)
{
checksum += buf[n];
}
if ( Config .includeEndCharInChecksum)
{
checksum += buf[end];
}
checksum = (((0x100 ‐ checksum) & 0x7F) | 0x40);
Here
is an example of an actual Checksum calculation for command 10
(Program kV setpoint)
The original message with a placeholder for the checksum is
<STX>10,4095,<CSUM><ETX>

First, you add up all the characters starting with the ‘1’ in the command
number, to the comma before the checksum with their ASCII values (in
hexadecimal):
0x31 + 0x30 + 0x2C + 0x34 + 0x30 + 0x39 + 0x35 + 0x2C = 0x18B

Next, you then take the two’s complement of that number by negating it,
by subtracting it from 0x100 (decimal 256), and only retain the lowest 7
bits by bitwise AND the results with 0x7F.
NOTE: This combines the steps of getting the twos complement, truncating the
result to 8 bits and clearing the 8
th
bit.
(0x100 – 0x18B) & 0x7F = 0x75

Finally, bitwise OR the result with 0x40:
0x75 | 0x40 = 0x75
The checksum byte is 0x75 (Decimal 117, ASCII: u)