CAS CI-150A, Owner'S Manual

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Communication Error Management
The management of communication data error must be controlled by CRC (cycle redundancy
check).
If a communication error occurs, the slave does not reply to any request.
The master must consider the time-out before receiving the reply. If no reply is received, it
can be inferred that a communication error has occurred.
If the data strings have been accurately received but cannot be executed, an exceptional
response is required. The contents are as follows.
Exceptional response
Address Function Code 2bytes
A Funct + 0x80 CRC
CODE DESCRIPTION
1 Invalid or unsupported function (ILLEGAL FUNCTION)
2 When the stated data address cannot be used (ILLEGAL DATA ADDRESS)
3 When the received data value is invalid (ILLEGAL DATA VALUE )
4 Error in the CRC code (CRC Error)