9 Communication
9.2 Modbus
149
SICAM MMU 7KG9663, Device Manual
E50417-H1040-C514-A3, Edition 01.2016
9.2
Modbus
When communicating via Ethernet, the Modbus TCP protocol is used. The Modbus specification with a detailed
explanation of the Modbus protocol is provided in:
•
Modbus over Serial Line
Specification & Implementation Guide
http://www.modbus.org
•
Modbus Application Protocol Specification
http://www.modbus.org
•
Modbus Messaging on TCP/IP Implementation Guide
http://www.modbus.org
9.2.1
Modbus Functions
The Modbus server of SICAM MMU supports the following Modbus functions:
9.2.2
Exception Responses
The Modbus server performs a series of consistency checks of the Modbus client requests, and if errors (e.g.
request to read a nonexistent register) are detected, it generates Modbus exception codes which are signaled
to the Modbus client in exception responses messages.
The messages contain the following codes:
Exception Code 01
ILLEGAL_FUNCTION
•
The Modbus client uses a function that is not supported by the Modbus server of the SICAM MMU (the
supported Modbus functions are listed in chapter 9.2.1).
Table 9-1
Supported Modbus Functions
Function
Number
Function
Name
Description
03
(03H)
Read Holding
Registers
Reading one or more holding registers from the Modbus server
Up to 125 registers can be read with one message.
06
(06H)
Write Single
Register
Writing a holding register
Function 16 is used for writing multiple holding register using one Modbus
message.
16
(10H)
Write Multiple
Registers
Writing one or more holding registers
Up to 123 registers can be written with one message.
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