GE 745 TRANSFORMER MANAGEMENT RELAY User Manual

8-10 745 Transformer Management Relay GE Power Management
8.2 MODBUS PROTOCOL 8 COMMUNICATIONS
8
8.2.13 EXCEPTION RESPONSES
Programming or operation errors happen because of illegal data in a message, hardware or software problems
in the slave device, etc. These errors result in an exception response from the slave. The slave detecting one
of these errors sends a response message to the master consisting of slave address, function code, error
code, and CRC. To indicate that the response is a notification of an error, the high order bit of the function code
is set to 1.
* Some implementations of Modbus may not support these exception responses.
MESSAGE FORMAT AND EXAMPLE:
Request to slave device 11 to perform unsupported function code 39h.
Table 8–3: ERROR CODES
ERROR
CODE
MODBUS DEFINITION GE POWER MANAGEMENT IMPLEMENTATION
01 ILLEGAL FUNCTION The function code of the master query message is not a function code
supported by the slave.
02 ILLEGAL DATA ADDRESS The address referenced in the data field of the master query message is not
an address supported by the slave.
03 ILLEGAL DATA VALUE The value referenced in the data field of the master query message is not
allowable in the addressed slave location.
04 FAILURE IN ASSOCIATED
DEVICE
An external device connected to the addressed slave device has failed and
the data requested cannot be sent. This response will be returned if a GE
Power Management device connected to the RS485 external device port of
the 745 has failed to respond to the 745.
05* ACKNOWLEDGE The addressed slave device has accepted and is processing a long duration
command. Poll for status.
06* BUSY, REJECTED
MESSAGE
The message was received without error, but the slave device is engaged in
processing a long duration command. Retransmit later, when the slave
device may be free.
07* NAK - NEGATIVE
ACKNOWLEDGE
The message was received without error, but the request could not be
performed, because this version of the 745 does not have the requested
operation available.
Master Query Message: Example (hex):
SLAVE ADDRESS 11 query message for slave 11
FUNCTION CODE 39 unsupported function code – error
CRC: low order byte CD
CRC: high order byte F2
Field: Example (hex):
SLAVE ADDRESS 11 response message from slave 11
FUNCTION CODE B9 return unsupported fn. code with high-order bit set
ERROR CODE 01 illegal function
CRC: low order byte 93
CRC: high order byte 95
NOTE

GE 745 TRANSFORMER MANAGEMENT RELAY Specifications

General

Brand	GE
Model	745 TRANSFORMER MANAGEMENT RELAY
Category	Relays
Language	English