Automationdirect.com Stellar SR44, User Manual

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Chapter 6: Serial Communications
6.5.5 – Read Exception Status (Modbus Function 07) – Starter 01
This function’s format is per the Modbus standard, but the bits in the value returned have different
meanings shown below. This is the quickest of the Modbus functions, and should be used in the
context of the SR44 to check if a station is present or check if it is busy.
6.5.6 – Returned Errors
If there is a communication error in the query, the SR44 does not reply.
If the network communication is OK, but for some reason the SR44 cannot correctly execute the
query, then it will return an error reply. In an error reply, the function byte is returned OR’ed with
80h, and the following byte contains the error number, e.g. if Function 07 cannot be executed,
87h will be returned.
Modbus Function 07 Transaction Table Showing Error Response
Query Response
Field Hex Byte Field Hex Byte
Slave Address 01 Slave Address 01
Function 07 Function 87
CRC Low 41 Exception Data 01
CRC High E2 CRC Low
PLC & SR44 automatically
calculate CRC checksum values
CRC High
Returned Error Response
Number Modbus Meaning
0 Illegal Function Writing
1 Illegal Data Address Out of allowed parameter range
2 Illegal Data Too many data bytes in query
3 Slave Busy Slave is performing a long command
Modbus Function 07 Transaction Table
Query Response
Field Hex Byte Field Hex Byte
Slave Address 01 Slave Address 01
Function 07 Function 07
CRC Low 41 Exception Data 00
CRC High E2 CRC Low
PLC & SR44 automatically
calculate CRC checksum values
CRC High
Returned Exception Data
Bit Meaning
0 Enabled
1 Stopped
2 Starting
3 Current Limiting
4 TOR (Start Complete)
5 Cooling
6 Alarm
7 Offline Command Failed
SR44 Series Soft Starter User Manual
1st Ed, Rev B 07/31/2019
6–18