Rockwell Automation 2755 Enhanced Decoder Series B - Manual (Page 312)

Appendix
C
Publication 2755-833
Transmission Check
The decoder can generate three types of transmission checks:
•
Longitudinal Redundancy Check
A byte developed by an exclusive OR of all bytes in a message.
•
Checksum, Most Significant Byte First
Sixteen bit sum of all the bytes in a message with the most significant
byte transmitted first.
•
Checksum, Least Significant Byte First
Sixteen bit sum of all the bytes in a message with the least
significant byte transmitted first.
The following example illustrates a transmission check. The
message contains the following data:
Start Character = *
Label Delimiter = $
End of Message = CR LF
Symbol Data = ABC
The message transmits in this sequence:
* $ A B C $ $ CR LF TRANSMISSION CHECK
The table below shows transmission checks for the message.
Transmission Check ASCII Character Hex Value Binary Value
* 2A 0010 1010
$ 24 0010 0100
A 41 0100 0001
B 42 0100 0010
C 43 0100 0011
$ 24 0010 0100
$ 24 0010 0100
CR OD 0000 1101
LF OA 0000 1010
LRC Check I 49 0100 1001
Checksum MSB SOH
s
01
73 0000 0001
0111 0011
Checksum LSB s
SOH
73
01 0111 0011
0000 0001
The sum of all bytes in the message is 173 Hex. Checksums are
transmitted in a sixteen bit format. The value 01 Hex is equivalent to
the ASCII control code SOH, 73 Hex is equivalent to the ASCII
character “s”.