Function Code 07: Read Device Status; Function Code 08: Loopback Test - GE 489 Instruction Manual

6 COMMUNICATIONS
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:
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
Note that if status is neither stopped or running, the generator is starting.
MESSAGE FORMAT AND EXAMPLE
Request status from slave 11.
MASTER TRANSMISSION:
SLAVE ADDRESS
FUNCTION CODE
CRC
SLAVE RESPONSE:
SLAVE ADDRESS
FUNCTION CODE
DEVICE STATUS
CRC
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.
MASTER TRANSMISSION:
SLAVE ADDRESS
FUNCTION CODE
DIAG CODE
DATA
CRC
SLAVE RESPONSE:
SLAVE ADDRESS
FUNCTION CODE
DIAG CODE
DATA
CRC
GE Multilin

6.2.5 FUNCTION CODE 07: READ DEVICE STATUS

BYTES EXAMPLE (HEX):
1 0B
1 07
2 47 42
BYTES EXAMPLE (HEX):
1 0B
1 07
1 59
2 C2 08
BYTES EXAMPLE (HEX):
1 0B
1 08
2 00 00
2 00 00
2 E0 A1
BYTES EXAMPLE (HEX):
1 0B
1 08
2 00 00
2 00 00
2 E0 A1
489 Generator Management Relay
6.2 MODBUS FUNCTIONS
message for slave 11
read device status
CRC calculated by the master
message for slave 11
read device status
status = 01011001 in binary
CRC calculated by the slave

6.2.6 FUNCTION CODE 08: LOOPBACK TEST

message for slave 11
loopback test
must be 00 00
must be 00 00
CRC calculated by the master
message for slave 11
loopback test
must be 00 00
must be 00 00
CRC calculated by the slave
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