Thread Starter


i was trying to connect a modbus device which is a annunciator panel using RS485 to RS232 converter. but i am getting a message on my modscan application as "Modbus exception response from slave device". Can anyone help me to solve this issue? has Modbus RTU capability (see near the bottom of the page) and CtrlTerm has nice logging features (see Modbus screen shot). If you are willing and able to use CtrlTerm to troubleshoot I am willing to help a bit.

Santosh Kubasad

The request is received without an error, but cannot be processed by the slave for another reason (may be illegal function code, illegal data address etc). Check if the FC is supported by the annunciator panel by looking at its users manual or if you are sending a request to a non-existing register or coil/discrete input The slave replies with an exception response.

Santosh Kubasad
Modbus Protocol Engineer
Colway Solutions(
Serveral reasons for exception requests are given below

Function code not supported

Starting Address == not OK
Starting Address + Quantity of Registers == not OK

Quantity of Registers > 125 or Quantity of Registers < 1

Device data mapping == not OK
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