Siemens floating-point representation data type 8

Siemens Floating points are supported only for inputs.

The Siemens PLC uses a special bitmap representation. The float bitmap representation is listed below:

Bits map: 31 30 29 28 27 26 25 24 23 22 21 20 ....................................01 00

Siemens: S X X X X X X X S M M M ...................................M M

where: S=Sign Bits, X=Exponent Bits, and M=Mantissa

Bit31 is the sign bit of the exponent.

Bit30 to Bit24 represent a decimal value of 26.....20 (64 ... 1) and are used to compose the exponent.

Bit23 is the sign bit of the mantissa,

bit22 to Bit00 represent a decimal value of 2-1...2-23and are used to compose the mantissa.

The following formula is used to generate the decimal value from the four bytes that are sent:

and the exponent:

The default is for the ModbusE interface to expect the high order register first.