Honeywell HC900 - Page 16

IEEE 32-bit Floating Point Register Information
IEEE Floating Point Data Format
8 HC900 Process Controller Communications User Guide Revision 13
April 2017
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:
1x2 x x2 x2 x2 x2 x2 x2
7 5 4 3 2 1 0
      0 2 0 0 0 1 0 1
6
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
6
 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
3F800000
0
00000000