Edwards Signaling 5530M-485 - Manual (Page 9)

P/N 3100345 ISSUE 2 PAGE 9
4.3 Calculating the checksum is done by first converting each ASCII character, found in the message string, to
the hexadecimal equivalent and then summing these characters. See below.
ASCII HEXADECIMAL
0 0x30
1 0x31
4 0x34
3 0x33
D 0x44
A 0x41
✓ (ACK) 0x06
(ETX) 0x03
0x156 hexadecimal total
4.4 Dropping the upper hexadecimal byte from the above total yields a final result of 56 hexadecimal. The
calculated hexadecimal checksum value should match the ASCII value received in the message string. If it
does not match, a possible error occurred during transmission and the message is considered unreliable.
The master or controlling computer should try to resend the message again.
Example of a POLL Command 43 issued to unit 05, Zone B
054300B
ASCII HEXADECIMAL
0 0x30
5 0x35
4 0x34
3 0x33
0 0x30
0 0x30
B 0x42
(ETX) 0x03
0x171 hexadecimal total
The calculated Message Block checksum are appended to the message string. Two bytes, ASCII 7 and
ASCII 1, consume these two checksum data fields. See below.
Send format: 054300A71
5.0 Wiring applications
RS-232 to RS-485 Multi or Single drop
RS-232 Port
DB9 F/M
(MCN485CB2323A9)
RS232/485 Converter
(MCN485CB2EOLT)
RS-485 cable
(up to 4000 ft)
Adaptatone
55XX-485Y6
Adaptatone
55XX-485Y6
Up to 32 units
(maximum)
IBM PC or Terminal