10 489 GENERATOR MANAGEMENT RELAY – COMMUNICATIONS GUIDE
CG.2.9 Error Responses
When a 489 detects an error other than a CRC error, a response will be sent to the master.
The MSbit of the Function Code byte will be set to 1 (i.e. the function code sent from the
slave will be equal to the function code sent from the master plus 128). The following byte
will be an exception code indicating the type of error that occurred.
Transmissions received from the master with CRC errors will be ignored by the 489.
The slave response to an error (other than CRC error) will be:
• SLAVE ADDRESS: 1 byte
• FUNCTION CODE: 1 byte (with MSbit set to 1)
• EXCEPTION CODE: 1 byte
•CRC: 2 bytes
The 489 implements the following exception response codes.
01: ILLEGAL FUNCTION
The function code transmitted is not one of the functions supported by the 489.
02: ILLEGAL DATA ADDRESS
The address referenced in the data field transmitted by the master is not an allowable
address for the 489.
03: ILLEGAL DATA VALUE
The value referenced in the data field transmitted by the master is not within range for the
selected data address.
Number of Setpoints 2 00 02 2 setpoints (4 bytes total)
CRC (low, high) 2 40 8A computed CRC error code
Slave Response Bytes Example Description
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