Date: 2021-08-17
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4. The slave receives a valid request that cannot be answered
This occurs if a requested register does not exist. If the slave unit receives a valid request, but the requested readings
are not available, the slave unit will respond a specific exception message in order to inform the master about the
reason for this error.
The CS141 provides these error codes:
o 02H - Illegal Data Address
The address data obtained with the valid request is not a valid address servable by the slave.
o 03H - Illegal Data Value
A contained value inside a valid request is not an allowed for this slave.
o 06H - Slave device busy
The slave has received a valid request, but is currently busy with a time-consuming or time-critical process.
As a result, he cannot serve the master for now. For the master, there is no reason to assume a timeout- he
will repeat the request sometime later.
How to configure Modbus
For this configuration step, navigate to the following menu:
Since Modbus is standardized, the basic configuration is intuitive to handle. To configure the Modbus agent, go to services and
open Modbus.
TCP Port 502
The TCP port 502 is a static port setting within the Modbus standard that cannot be changed or customized without leaving
standards - This port value is hardcoded inside the CS141 source code.
Slave Address
The Modbus slave is the ID that make a Modbus device addressable. The Slave ID mentioned by a master's query will cause
this device to answer This ID may be customized, but only exist once inside a Modbus network.
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