Finisar AN-2030 - Manual (Page 23)

AN-2030: Digital Diagnostic Monitoring Interface for Optical Transceivers
F i n i s a r
9/26/02 Revision D Page 23
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Table 3.16c: IEEE-754 Single-Precision Floating Point Number Format 2
FUNCTION SIGN EXPONENT MANTISSA
BIT 31 30……………………23 22……………………………………………………………0
BYTE 3 2 1 0
ß Most Significant Least Significant à
3
4
5
6
7
Rx_PWR(4), as an example, is stored as in Table 3.16d. 8
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Table 3.16d: Example of Floating Point Representation 10
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BYTE
ADDRESS
CONTENTS SIGNIFICANCE
56 SEEEEEEE Most
57 EMMMMMMM 2
nd
Most
58 MMMMMMMM 2
nd
Least
59 MMMMMMMM Least
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13
where S = sign bit; E = exponent bit; M = mantissa bit. 14
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Special cases of the various bit values are reserved to represent indeterminate values 16
such as positive and negative infinity; zero; and “NaN”or not a number. NaN indicates 17
an invalid result. As of this writing, explanations of the IEEE single precision floating 18
point format were posted on the worldwide web at 19
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http://www.psc.edu/general/software/packages/ieee/ieee.html 21
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and 23
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http://research.microsoft.com/~hollasch/cgindex/coding/ieeefloat.html . 25
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The actual IEEE standard is available at www.IEEE.org . 27