TwinCAT convert two Modbus 16-bit registers to REAL

Hello,

First, please excuse my question I am new to Modbus.

I have a CX-5140 control unit from Beckhoff and an instrumentation device that measures (Temperature, Humidity, etc.).

The device can function as a Modbus slave and hence I am using EL6021 EtherCAT terminal & TwinCAT Modbus RTU library to receive data from the device. The device has 36 registers of data all are 16-bit. In the data sheet of the device, each two registers represents a measured parameter ( for example: register 1 and register 2 are temperature....register 3 and register 4 are humidity ....and so on).

I was able to read the data from the device successfully in an array like so:

arrReceivedData : Array [1..40] of WORD;


Now my question is:
How can I combine any two registers such as arrReceivedData[2] and arrReceivedData[3] into another REAL variable??

In C++ world, I could easily use functions and macros such as HIWORD(something) & LOWORD(something) to re-write a 32-bit data type like "int" by using two 16-bit data type like "short" ....but there is no such function blocks in PLC or CX world to do so.

Thank you all.

In classic C this is a case where you would use a union. I'm not sure if TwinCAT has a system function to produce a REAL from two 16-bit WORDs but I'm pretty sure Codesys supports unions.

Keith

There are probably several ways to do this in TwinCAT. I haven't worked with with unions as mentioned by kamenges, but it appears to be supported:
https://infosys.beckhoff.com/englis..._intro/2529421195.html&id=2192070974948030363

You could also do a straight byte copy:
This assumes that 'destReal' is defined as a 4-byte REAL variable, and the data in the two array words is already in REAL format but just split into 16-bit groups. Be careful with Memcpy because you can crash your controller if your offsets aren't right.

CODESYS