KEYENCE N-400 - Manual (Page 143)

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Appendices
Appendices
Appendix G Checksum Calculation Method
You can add a checksum to transmitted data. (The checksum cannot be added to a
command or a response to a command.)
Adding a checksum enables incorrect data translation to be detected in the RS-
232C communication. If the checksum does not match when the PASS/RTRY or
ACK/NAK protocol is used, modify the program so that the “Request to resend”
(RTRY or NAK) command is sent to the N-400. To set the checksum, use the
“PROTOCOL SETUP” screen of the N-400 setup software. (The checksum cannot
be added when the PLC link is used.)
■ Checksum calculation range and the position to add checksum
The checksum calculation is performed with all characters except for the header
and delimiter. The checksum is added immediately before the delimiter.
CC = Checksum (Two ASCII code characters)
• Data communication in multi-drop link mode
• Data communication in multi-head mode
■ Checksum calculation method
Example:
Calculate the checksum (CC) in the above example.
Convert each character into the ASCII code as shown below, and express the
result as 8-bit binary numbers.
Calculate the “Exclusive-OR” of the binary numbers of each bit.
Header % P mm CC – Delimiter Read Data
Calculation range
Result
Header CC Delimeter Read Data
Calculation range
Result
* Based on the “Exclusive OR” logic,
when an odd number of “1”s are
present, the calculation result is “1”,
and when an even number of “1”s
are present, the calculation result is
“0”.
Header % P 01 CC – Delimiter AB12
% 25h 0010 0101
P 50h 0101 0000
0 30h 0011 0000
1 31h 0011 0001
– 2Dh 0010 1101
A 41h 0100 0001
B 42h 0100 0010
1 31h 0011 0001
2 32h 0011 0010
0101 1001 59h
+
ASCII code
(Hexadecimal) Binary
Data