Modbus; Modbus Functions - Siemens 7XV5673 Device Manual

8.2

Modbus

For the communication via the Ethernet interface, the Modbus TCP protocol or Modbus UDP protocol is used.
For serial FO and RS485 interface, the Modbus RTU 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
The following features are implemented in the SICAM I/O Unit:
• Modbus TCP server
• Modbus UDP server
• Modbus UDP client (only I/O mirror function)
• Modbus RTU master (only I/O mirror function)
• Modbus RTU slave
• Support of the Modbus function codes 3, 6, 16, and 23
• Support of the data types: ASCII strings, date/time, indications, controllable indications, and command
8.2.1

Modbus Functions

NOTE
The Modbus functions are the same for Modbus TCP and Modbus UDP (Ethernet) and Modbus RTU (serial).
The Modbus server of SICAM I/O Unit supports the following Modbus functions:
Table 8-1
Function
Number
03
(03H)
06
(06H)
16
(10H)
23
(17H)
SICAM I/O Unit, 7XV5673, Device Manual
E50417-H1040-C484-A3, Edition 05.2012
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.
Preset Single Writing of value in a single holding register
Register
Function 16 is used for writing several holding registers via a Modbus
telegram.
Preset Writing of values in several holding register (sequential)
Multiple
Registers A maximum of 123 registers can be written with a telegram.
Read/Write Combination of writing (request indication) and reading (answer indication)
4x Registers in one or more holding registers; writing and reading do not have to take
place in the same register.
Description
8 Communication
8.2 Modbus
139