Modbus RTU Communications Protocol
F-13
SEL-300G Instruction Manual
Date Code 20060731
Table F.13: 07h Read Exception Status Command
Bytes Field
Requests from the master must have the following format:
1 byte
Slave Address
1 byte
Function Code (07h)
0 bytes
No Data Fields Are Sent
2 bytes
CRC-16
A successful response from the slave will have the following format:
1 byte
Slave Address
1 byte
Function Code (07h)
1 byte
Status Byte
2 bytes
CRC-16
The status byte is sent least significant bit first, and consists of the
following bits:
Bit 0
OUT1 Status
Bit 1
OUT2 Status
Bit 2
OUT3 Status
Bit 3
OUT4 Status
Bit 4
Alarm Output status
Bit 5
Input 1 Status
Bit 6
Input 2 Status
Bit 7
Relay Status
If the status bit is set to 1, the following are true for the status indicated by the bit:
•
Alarm contact is asserted.
•
Relay is disabled.
If the status bit is set to 0, the following are true for the status indicated by the bit:
•
Alarm contact is deasserted.
•
Relay is enabled.
The relay response to errors in the query is shown below:
Error
Error Code
Returned
Communication
Counter Increments
Format error
Illegal Data Value
(03h)
Bad Packet Format
08h Loopback Diagnostic Command
The SEL-300G uses this function to allow a Modbus master to perform a diagnostic test on the
Modbus communications channel and relay. When the subfunction field is 0000h, the relay
returns a replica of the received message.
Summary of Contents for SEL-300G
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