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2.5 Modbus Validation (Continued)
In this instance, the green 'LEDs' are lit signifying slave ID and Function Code (fc)
match. The data is found and displayed properly, and the cyclic redundancy check
(CRC) – or checksum was completed successfully.
The circled section in the log shows >>> Question from DCM and < Response from
simulator/ PLC
This is an example of bad communicatons
In this instance, the Modbus wires are incorrect, and must be swapped.
The first 2 pairs of Hex values should match Slave ID (01) and function code (04) of the
DCM.
The 'LEDs' are out signifying it is not set up correct, as can be seen with no response
given.
The circled section in the log shows >>> Question from DCM. There is no response from
simulator/ PLC
19
Installation
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