Description Of The Modbus Functions - WAGO 750-341 Manual

6.3 Description of the MODBUS Functions

All MODBUS functions in the WAGO ETHERNET fieldbus coupler and
controller are executed as follows:
A MODBUS TCP master (e.g., a PC) makes a request to the fieldbus coupler
using a specific function code based on the desired operation. The fieldbus
coupler receives the datagram and then responds to the master with the proper
data, which is based on the master's request.
If the coupler receives an incorrect request, it sends an error datagram
(Exception) to the master.
The exception code contained in the exception has the following meaning:
Exception Code
The following chapters describe the datagram architecture of request, response
and exception with examples for each function code.
Note
In the case of the read/write functions (FC1 – FC4) the outputs can be
additionally written and read back by adding an offset of 200
MODBUS addresses in the range of [0
(0x01000) to the MODBUS addresses in the range of [6000
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
Meaning
0x01 Illegal Function
0x02 Illegal Data Address
0x03 Illegal Data Value
0x04 Slave Device Failure
MODBUS Functions
Description of the MODBUS Functions
- FF ] and an offset of 1000
hex hex
• 133
(0x0200) to the
hex
hex
- 62FB ].
hex hex