Common issues faced by Modbus driver: Registers addresses indexation.

Question:

A common problem faced by Modicon Modbus Master driver is the following: communication takes place as usual, however the values to be read are different from the ones expected. This can happen due to discrepancies in the indexation of addresses of registers used by Modbus driver and the device. This situation can happen especially when reading FLOAT-type variables. How can I fix this?

 

Solution:

The indexation of addresses of registers at Modbus driver can start at two points: from 0, or from 1.  If the driver’s indexation doesn’t match the right values, the driver may end up reading some incorrect values , or even accessing invalid addresses. It is crucial, therefore, that the indexation begin right from the expected value, be it 0 or 1.

To work around this situation, you can use the driver’s configuration window to access the Modbus tab and then check the Data Address Model Offset option according to the device’s addressing standard (whether it starts in 0 or it starts in 1). To find out the device’s addressing standard, you must check the corresponding documentation supplied by its vendor.

Registers addresses indexation at Modbus

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