Using Modbus register addresses directly
Usually, it is necessary to enter Modbus registered address decremented by 1 as "start address",
but it may lead to confusion when comparing the data point's "start address" with the registered
address from Modbus device's manual. Therefore, enter a negative value in the "response
address offset" field to directly use the registered address from the Modbus device's manual as
"start address". In case a negative value has been entered as "response address offset", this value
will internally be subtracted from the given "start address" number to read the data from
Modbus device. Positive "response address offset" values will be handled to address specific data
within the read data if several registers need to be read to acquire the data from Modbus device
as data block and the necessary data itself is only a part of that data block.
Supported since:
MindConnect Nano V03.04.03.03 b001
Samples:
Using decremented
start address
Using address
from manual
Getting data from a read
data block
Registered address from Modbus
device manual
303 303 64001
Start address 302 303
64001
1)
Quantity 1 1 27
Response address offset 0 -1 11
Response quantity 1 1 16
1)
Sample start offset as documented in SENTRON PAC manual - can be used without
decrementing it by 1.
4.5 Overview of Modbus RTU protocol for MindConnect Nano
The Modbus protocol is supported for the MindConnect Nano plugin. You can select the
protocol type Modbus RTU while adding a new data source in Asset Manager.
Modbus configuration
The Modbus configuration view is only visible after a successful onboarding of the
MindConnect Nano. The MindConnect Nano Version must be higher than V3.3.0.2.
The following picture shows the protocol selection in Asset Manager:
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