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GE Multilin 489 Generator Management Relay 6-5
6 COMMUNICATIONS 6.2 MODBUS FUNCTIONS
6
6.2.5 FUNCTION CODE 07: READ DEVICE STATUS
Modbus Implementation: Read Exception Status
489 Implementation: Read Device Status
This function reads the selected device status. A short message length allows for rapid reading of status. The returned sta-
tus byte has individual bits set to 1 or 0 depending on the slave device status. The 489 general status byte is shown below:
Note that if status is neither stopped or running, the generator is starting.
MESSAGE FORMAT AND EXAMPLE
Request status from slave 11.
6.2.6 FUNCTION CODE 08: LOOPBACK TEST
Modbus Implementation: Loopback Test
489 Implementation: Loopback Test
This function is used to test the integrity of the communication link. The 489 will echo the request.
MESSAGE FORMAT AND EXAMPLE
Loopback test from slave 11.
BIT NO. DESCRIPTION
B0 R1 Trip relay operated = 1
B1 R2 Auxiliary relay operated = 1
B2 R3 Auxiliary relay operated = 1
B3 R4 Auxiliary relay operated = 1
B4 R5 Alarm start relay operated = 1
B5 R6 Service relay operated = 1
B6 Stopped = 1
B7 Running = 1
MASTER TRANSMISSION: BYTES EXAMPLE (HEX):
SLAVE ADDRESS 1 0B message for slave 11
FUNCTION CODE 1 07 read device status
CRC 2 47 42 CRC calculated by the master
SLAVE RESPONSE: BYTES EXAMPLE (HEX):
SLAVE ADDRESS 1 0B message for slave 11
FUNCTION CODE 1 07 read device status
DEVICE STATUS 1 59 status = 01011001 in binary
CRC 2 C2 08 CRC calculated by the slave
MASTER TRANSMISSION: BYTES EXAMPLE (HEX):
SLAVE ADDRESS 1 0B message for slave 11
FUNCTION CODE 1 08 loopback test
DIAG CODE 2 00 00 must be 00 00
DATA 2 00 00 must be 00 00
CRC 2 E0 A1 CRC calculated by the master
SLAVE RESPONSE: BYTES EXAMPLE (HEX):
SLAVE ADDRESS 1 0B message for slave 11
FUNCTION CODE 1 08 loopback test
DIAG CODE 2 00 00 must be 00 00
DATA 2 00 00 must be 00 00
CRC 2 E0 A1 CRC calculated by the slave