Version: 2020-09-04
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3. Master or slave will send invalid queries / answers
Such a phenomenon can occur if the termination resistors are not set up correctly: Although data is being sent, there are clear
parity, LRC, or CRC errors within the data packet. Since invalid packets are discarded, the slave will usually ignore an invalid
request without answering. However, the master's reaction will differ: In general, he will handle a faulty slave response with a
corresponding timeout message.
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 some time 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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