Schneider Electric LXM32M Modbus response to a Modbus request, Excep Name Description Tion Code

3 Basics LXM32M

3.3.2Modbus response to a Modbus request

The Modus server generates a Modbus response after having pro- cessed a Modbus request.

Depending on the type of processing, two types of Modbus responses are possible:

•Positive Modbus response

-The "Function Code" in the Modbus response corresponds to the "Function Code" in the Modbus request.

•Negative Modbus response

-The client receives pertinent information on error detection dur- ing processing;

-The "Function Code" in Modbus response corresponds to the "Function Code" in the Modbus request + 80h.

-The "Exception Code" indicates the cause of the error.

If a syntactically incorrect Modbus PDU (Protocol Data Unit) is trans- mitted, the connection is terminated. In the case of other other error, a negative Modbus response is sent.

Excep-	Name	Description
tion Code
01	Illegal Function Code	The "Function Code" is unknown to the
		server.
02	Illegal Data Address	Depends on the Modbus request
03	Illegal Data Value	Depends on the Modbus request
04	Server Failure	The server was unable to properly termi-
		nate processing.
05	Acknowledge	The server has accepted the Modbus
		request. However, the execution takes a
		relatively long time. The server therefore
		only returns an acknowledgement con-
		firming receipt of the service request.
06	Server Busy	The server was unable to accept the
		Modbus request. It is the responsibility of
		the application on the client to determine
		whether and when to re-send the request.
0A	Gateway Problem	The gateway path is unavailable.
0B	Gateway Problem	The targeted device does not respond.
		The gateway generates this error.

0198441113843, V1.01, 01.2012

20 Modbus-TCP module