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

6.2 SUPPORTED MODBUS FUNCTIONS
Modbus Implementation:
489 Implementation:
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
6
DEVICE STATUS
CRC
Modbus Implementation:
489 Implementation:
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
6-6
Read Exception Status
Read Device Status
BYTES
1
1
2
BYTES
1
1
1
2
Loopback Test
Loopback Test
BYTES
1
1
2
2
2
BYTES
1
1
2
2
2
489 Generator Management Relay

6.2.5 FUNCTION CODE 07: READ DEVICE STATUS

EXAMPLE (HEX):
0B message for slave 11
07 read device status
47 42 CRC calculated by the master
EXAMPLE (HEX):
0B message for slave 11
07 read device status
59 status = 01011001 in binary
C2 08 CRC calculated by the slave

6.2.6 FUNCTION CODE 08: LOOPBACK TEST

EXAMPLE (HEX):
0B message for slave 11
08 loopback test
00 00 must be 00 00
00 00 must be 00 00
E0 A1 CRC calculated by the master
EXAMPLE (HEX):
0B message for slave 11
08 loopback test
00 00 must be 00 00
00 00 must be 00 00
E0 A1 CRC calculated by the slave
6 COMMUNICATIONS
GE Power Management