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266CRH / 266CRT, 266CSH / 266CST MULTIVARIABLE PRESSURE TRANSMITTER | OI/266CXX/MODBUS-EN REV. A
Modbus register tables
All registers in this document are referenced to one.
The Modbus messages are referenced to zero.
This means that the number of the mapped register is one
higher than the number that is sent in a Modbus message frame.
There is a difference between function code 3 and
function code 4:
•
Function code 4 can be executed in less time than
function code 3. Function code 4 is meant to access the
process parameters, which possibly could be polled in a
low cycle time (>100ms). Therefore, the data of the
parameters is held in an internal buffer, which has a low
access time.
•
Function code 3 should be used to access parameters
non-cyclic or with a high cycle time (>seconds).
By reading or writing 32 bit or 16 bit registers 4 or 2 bytes are
transmitted. If a parameter has a datatype which uses less bytes
than that, the data is transmitted in the lower data bytes of the
Modbus message frame. The data bytes, that are not used, are
set to zero.
To access the following parameters the device mode must be set
to 'Operate'.
Change from two to one column
69
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