Communication
2.2 Modbus
18 SICAM Q100, 7KG95xx, System Manual
E50417-C1040-C522-A8, Edition 09.2020
2.2 Modbus
2.2.1 Modbus Functions for Modbus TCP Server and Modbus RTU Slave
The Modbus TCP server of SICAM Q100 supports the following Modbus functions:
2.2.2 Exception Responses for Modbus TCP Server and Modbus RTU Slave
The Modbus server performs a series of consistency checks of the Modbus client requests, and if errors (for
example 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 Q100. The
supported Modbus functions are listed in chapter .
Exception Code 02 ILLEGAL_DATA_ADDRESS
• An attempt is made to read out or write to a nonexistent Modbus register (see chapter 2.2.7, Modbus
mapping for valid registers).
• An attempt is made to read out or write to too many registers. A Modbus message enables reading out
125 holding registers and writing to 123 holding registers maximum.
• The Modbus client tries to write to a register in the Modbus server for which only read access is allowed
according to the Modbus mapping (see chapter 2.2.7).
NOTE
The Modbus functions are the same for Modbus TCP (Ethernet) and Modbus RTU (serial).
Table 2-1 Supported Modbus TCP Server 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.
NOTE
The exception responses for Modbus TCP (Ethernet) and Modbus RTU (serial) are the same.
SYS_SICAM_Q100_US.book Page 18 Thursday, September 24, 2020 1:17 PM
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