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Modbus RTU Message Format

02/13 Modbus® RTU Serial Communications User Manual 5

Exponent

The exponent is defined by an unsigned 8-bit binary value (bits 23 through 30). The value of the exponent

is derived by performing a signed subtraction of 127 (decimal) from the 8-bit exponent value.

DECIMAL HEXADECIMAL BINARY

100 42C80000 01000010 11001000 00000000 00000000

removing the sign and mantissa bits, the exponent becomes:

DECIMAL HEXADECIMAL BINARY

133 85 x1000010 1xxxxxxx xxxxxxxx xxxxxxxx

or:

1x2x x2x2x2x2x2x2

7543210

+++++++02 0 0 0 1 0 1

Subtract a bias of 127 (decimal) from the exponent to determine its value: 133 – 127 = 6.

Mantissa and Exponent Combination

Combining the mantissa and exponent from the two previous examples:

float number = mantissa x 2

float number = 1.5625 x 2 x 64 = 100.0

exponent

= 15625.

Below is a list of sample float values in IEEE format:

DECIMAL HEXADECIMAL

100.0 42C80000

-100.0 C2C80000

0.5 3F000000

-1.75 BFE00000

0.0625 3D800000

1.0 3F800000

0.0 00000000

2.0 40000000

55.32 425047AE

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 75 76

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Siemens NAN 67 Series Manuel d'utilisateur Page 11