Message Exchange Formats
32 RS232 Communications Reference Manual 8/99
4.6 Floating Point Format
Floating point format is per the IEEE Standard for Binary Floating Point Arithmetic (TASK P754). This
format conforms to that of the Unit’s Math Firmware and/or Co-Processor.
4.6.1 IEEE 754 Format
The Floating Point data format consists of four contiguous bytes containing a 23-bit signed binary mantissa
with an 8-bit biased binary exponent. The bits are numbered from 31 to 0, left to right. Byte 4 contains bits
31-24, byte 3 contains bits 23 to 16, and so on. A description of the layout and accompanying figure follow:
BITS DESCRIPTION
0-22 Mantissa
23-30 Exponent: 8-bit unsigned value
31 Sign of the mantissa:
0 = positive, 1 = negative
An implied binary point exists between bits 22 and 23. Note that the transmission order is byte 1 to byte 4.
byte 4 byte 3 byte 2 byte 1
3 2 2 1 1
1 4 3 6 5 8 7 0
xxxxxxxx x.xxxxxxx xxxxxxxx xxxxxxx
mantissa (23 bits)
implied binary point
exponent
sign of the mantissa
The formula for calculating the floating point number is:
+−
.
2
exponent
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