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
Содержание Stellar SR44
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