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
0x1
56
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
<STX>054300B<ETX>
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:
<STX>054300A<ETX>
71
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
