Modbus; Modbus Functions; Exception Responses - Siemens SICAM MMU 7KG9663 Device Manual

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:
Table 9-1
Function
Number
03
(03H)
06
(06H)
16
(10H)
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).
SICAM MMU 7KG9663, Device Manual
E50417-H1040-C514-A3, Edition 01.2016
Supported Modbus Functions
Function
Name
Read Holding Reading one or more holding registers from the Modbus server
Registers
Up to 125 registers can be read with one message.
Write Single Writing a holding register
Register
Function 16 is used for writing multiple holding register using one Modbus
message.
Write Multiple Writing one or more holding registers
Registers
Up to 123 registers can be written with one message.
Description
9 Communication
9.2 Modbus
149