Could you please provide a screenshot for com mod mast to read float value?
You can't read directly float values by using of COM_MOD_MAST - that is serial Modbus RTU. So you can transfer only bits (coils) and words (registers). Usually float values are transferred by means of one or two consequence words - check your slave's mapping.
Here is example for reading of 2 consequence words and transfer them to real:
Provide pulses on EN input.
COM_PORT: BYTE := 1;
SLAVE_ADD_VF1: BYTE := 1;
FCT_READ: BYTE := 3;
TIME_OUT: WORD := 300;
START_ADDRESS_ANSW: WORD := 0;
NUMBER_REG_READ: WORD := 2;
If you use structured data type with different data types eg. first variable type int (16 bit), second variable type real (32 bit) then AC500 will create an empty 16 bit space between first and second variable. You can't see this "feature" in simulation mode, only when you are in online.