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ICC
11.12.2.3
Modbus RTU Sniffer
11.12.2.3.1 Overview
The gateway supports a Modbus RTU sniffer driver on its RS-485 port. This
driver enables fully non-intrusive insight into any existing Modbus RTU network
consisting of a master and at least one slave. The driver can be configured to
“sniff” the requests of the master and log the responses of the slave(s) into the
database. Some notes of interest are:
•
Supported Modbus functions are indicated in Table 13.
Table 13: Supported Modbus RTU Sniffer Functions
Function
Code
Function
03
Read Holding Registers
04
Read Input Registers
06
Preset Single Register
16
Force Multiple Registers
•
The filtering of specific actions targeting registers of interest is fully
configurable through service objects.
•
Both Holding and Input Registers are supported in Modbus Service Objects.
•
The Modbus Sniffer Service Objects are identical to those of the Modbus
Master Service Objects with the exception that instead of the gateway itself
generating requests, it must rely on the existing Modbus master to make
requests on its behalf. Therefore, if the master never reads or writes a
certain register that is configured in a service object on the gateway, the
value of that register will never be updated. For more information on
Modbus Service Objects, refer to section 8.8.13.2.
•
The Modbus Sniffer driver never transmits on the Modbus network being
sniffed.
