Hello, I got a device from which I require to read values from I am using a WAGO PLC 750-8212 and I am communicating through Modbus Master FUNCTION BLOCK from library WagoAppPLCModbus in Codesys 3.5 to this device. I already receive data from the device that is a CVM to monitor voltage from a fuel cell. The technical support of the company that makes these devices says that the data is sent in little endian form. And I want to convert it to a float value. The tech support sent me the next instructions of how to do it but I am new using codesys, so any advice or help I will really appreciate so much.

Message from tech support:
The process is complicated, better to do it with already implemented library in the language/program you use.

Basically the process should be next:

To convert the two Modbus registers containing parts of a 32-bit float in little-endian byte order to a floating-point number using mathematical operations, you first need to combine the two 16-bit integers (assuming reg1 is the lower word and reg2 is the higher word) and then interpret the result according to the IEEE 754 standard.

Given:
- Register 192 (reg1) = 4096
- Register 193 (reg2) = 14884

Step 1: Combine the two registers. Since we are dealing with little-endian byte order, reg2 is the high word, and reg1 is the low word:

combined = reg2 * 2^16 + reg1
combined = 14884 * 65536 + 4096
combined = 975175680 + 4096
combined = 975179776

Step 2: Convert the combined value to binary:

combined_binary = '1110101101011100000000000000000'

Step 3: Split the binary into IEEE 754 components:

• Sign bit (1 bit): 0
• Exponent (8 bits): 11101011
• Mantissa (23 bits): 01011100000000000000000

Step 4: Convert the binary exponent to decimal and subtract the bias (127 for 32-bit floats):

exponent = int('11101011', 2) - 127
exponent = 235 - 127
exponent = 108

Step 5: Calculate the mantissa as a fraction:

The mantissa in IEEE 754 format is the fractional part after the leading 1 (which is implicit). Therefore, we need to convert the binary mantissa to decimal and add the implicit leading 1:

mantissa_fractional = 1 + int('01011100000000000000000', 2) / 2^23
mantissa_fractional = 1 + 18688 / 8388608
mantissa_fractional = 1 + 0.002227783203125
mantissa_fractional ≈ 1.002227783203125

Step 6: Combine the sign, exponent, and mantissa to get the float value:

float_value = (-1)^0 * mantissa_fractional * 2^exponent
float_value = 1 * 1.002227783203125 * 2^108

Because the exponent is quite large, the resulting float value is a very large number.

Maybe try going back to step one and:

Var
    Reg1: WORD;
    Reg2: WORD;
    Reg12: DWORD;
    Value: REAL;
end_var

// program
Reg1:= 4096;
Reg2:= 14884;
Reg12:= (reg2 * 65536) + reg1;
Value:= DWORD_TO_REAL(Reg12);