8-10 SR3 SERIES PROTECTIVE RELAY PLATFORM – COMMUNICATIONS GUIDE
FUNCTION CODE 07H CHAPTER 8: MODBUS FUNCTIONS
Function Code 07H
Modbus Implementation: Read Exception Status
3 Series relay Implementation: Read Device Status
This is a function used to quickly read the status of a selected device. A short message
length allows for rapid reading of status. The status byte returned will have individual bits
set to 1 or 0 depending on the status of the slave device. For this example, consider the
following 3 Series relay
general status byte:
The master/slave packets have the following format:
Table 8-5: Function code 7 bitmask
Table 8-6: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 07H
Query:
Response:
Bit Function
0 Alarm
1 Trip
2 Self Test
3 Breaker Connected
4 52a Contact
5 52b Contact
6 Maintenance
7 Relay in Service
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 07 read device status
CRC 2 4C 22 CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave
17
FUNCTION CODE 1 07 read device status
DEVICE STATUS (see definition
above)
1 2C status = 00101100 (in
binary)
CRC 2 22 28 CRC error code
Field Name Hex
Slave Address FE
Function 07
Field Name Hex
Slave Address FE
Function 07
Device Status (see definition above) 2C
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