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Floating-point Math Instructions Section 5-24
The floating-point data format conforms to the IEEE754 standards. Data is
expressed in 32 bits, as follows:
Number of Digits The number of effective digits for floating-point data is 24 bits for binary
(approximately seven digits decimal).
Floating-point Data The following data can be expressed by floating-point data:
•–
∞
• –3.402823 x 10
38
≤ value ≤ –1.175494 x 10
–38
•0
• 1.175494 x 10
–38
≤ value ≤ 3.402823 x 10
38
•+∞
• Not a number (NaN)
Special Numbers The formats for NaN,
±∞, and 0 are as follows:
NaN*: e = 255, f
≠ 0
+
∞: e = 255, f = 0, s= 0
–
∞: e = 255, f = 0, s= 1
0: e = 0
*NaN (not a number) is not a valid floating-point number. Executing floating-
point calculation instructions will not result in NaN.
Writing Floating-point
Data
When floating-point is specified for the data format in the I/O memory edit dis-
play in the CX-Programmer, standard decimal numbers input in the display
are automatically converted to the floating-point format shown above
(IEEE754-format) and written to I/O Memory. Data written in the IEEE754-for-
mat is automatically converted to standard decimal format when monitored on
the display.
It isn’t necessary for the user to be aware of the IEEE754 data format when
reading and writing floating-point data. It is only necessary to remember that
floating point values occupy two words each.
Data No. of bits Contents
s: sign 1 0: positive; 1: negative
e: exponent 8 The exponent (e) value ranges from 0 to 255.
The actual exponent is the value remaining after
127 is subtracted from e, resulting in a range of –
127 to 128. “e=0” and “e=255” express special
numbers.
f: mantissa 23 The mantissa portion of binary floating-point
data fits the formal 2.0 > 1.f ≥1.0.
Sign
sf
Exponent Mantissa
31 30 23 22 0
e
1.175494 x 10
38
1.175494 x 10
38
−∞
+
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