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Modbus Functions489
Communications Guide
http://www.GEindustrial.com/multilin
6
GE Multilin
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 status 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.
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 DESCRIPTION BIT DESCRIPTION
B0 1 TRIP relay operated = 1 B4 5 ALARM relay operated = 1
B1 2 AUXILIARY relay operated = 1 B5 6 SERVICE relay operated = 1
B2 3 AUXILIARY relay operated = 1 B6 Stopped = 1
B3 4 AUXILIARY relay operated = 1 B7 Running = 1
Master Transmission Bytes Example Description
Slave Address 1 0B message for slave 11
Function Code 1 07 read device status
CRC (low, high) 2 47 42 computed CRC error code
Slave Response Bytes Example Description
Slave Address 1 0B message from slave 11
Function Code 1 07 read device status
Device Status 1 59 status = 01011001b
CRC (low, high) 2 C2 08 computed CRC error code
Master Transmission Bytes Example Description
Slave Address 1 0B message for slave 11
Function Code 1 08 loopback test
Diagnostic Code 2 00 00 must be 0000h
Data 2 00 00 must be 0000h
CRC (low, high) 2 E0 A1 computed CRC error code
Slave Response Bytes Example Description
Slave Address 1 0B message from slave 11
Function Code 1 08 loopback test
Diagnostic Code 2 00 00 must be 0000h
Data 2 00 00 must be 0000h
CRC (low, high) 2 E0 A1 computed CRC error code