IDEC MICROSmart FC6A Series - Page 253

FC6A S ERIES MICROS MART L ADDER P ROGRAMMING M ANUAL FC9Y-B1726 12-5
12: D ISPLAY I NSTRUCTIONS
Floating Point Value Notation on LCD
Whether or not F (float) LCD notation uses decimal notation or exponent notation is determined according to the single-
precision floating point definition in IEEE 754 and the internal system function included in the CPU module.
The IEEE 754 single precision format consists of three fields: a 23-bit fraction, f; an 8-bit biased exponent, e; and 1-bit sign,
s. These fields are stored contiguously in one 32-bit word, as shown in the figure below. Bits 0:22 contain the 23-bit fraction,
f, with bit 0 being the least significant bit of the fraction and bit 22 being the most significant; bits 23:30 contain the 8-bit
biased exponent, e, with bit 23 being the least significant bit of the biased exponent and bit 30 being the most significant;
and the highest-order bit 31 contains the sign bit, s.
The table below shows the correspondence between the values of the three constituent fields s, e, and f and the value
represented by the single precision format bit pattern.
When the value is ±0, denormalized number, or normalized number, the value is displayed according to the internal system
function of the CPU module.
Example: This table shows the representation on the LCD for the following floating-point values.
Value Exponent Field e Fraction Field f Representation
±0 e=0 f=0 0
Denormal numbers e=0 f≈0•Displayed in decimal notation
0.0001 ≤ | Value | < 9,999,999.5
(Number of significant digits is 7 digits, 8th
digit is rounded)
• Displayed in exponent notation
| Value | < 0.0001
| Value | ≥ 9,999,999.5
Normal numbers 0<e<255 Arbitrary
±∞ (± infinities)
e=255
f=0 INF
NaNs (Not a number) f≈0NAN
Value Representation in LCD
1234567 1234567
12345678 1.234568E+07
1234567.8 1234568
0.0001 0.0001
0.00001 1E-05
0.000001 1E-06
0.0000001 1E-07
0.123456 0.123456
0.1234567 0.1234567
0.12345678 0.1234568
0.0000012 1.2E-06
1.2345678 1.234568
00
0.0001234568 0.0001234568
s e[30:23] f[22:0]
31 30 23 22 0
23-bit fraction8-bit biased exponent
Sign bit (0: positive, 1: negative)
Bit Bit Bit Bit Bit