IDEC microsmart pentra, Programming Manual

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FT1A S
MART
A
XIS
U
SER
’
S
M
ANUAL
FT9Y-B1382 4-11
4: I
NSTRUCTIONS
R
EFERENCE
Floating-Point Data Format
The SmartAxis can specify the floating-point data type (F) for advanced instructions. Like the double word (D) and long integer (L)
data types, the floating-point data type also uses two consecutive data registers to execute advanced instructions. The SmartAxis
supports the floating-point data based on the single storage format of the IEEE (The Institute of Electrical and Electronics
Engineers) Standard 754.
Single Storage Format
The IEEE single storage 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 storage format bit pattern. When any value out of the bit pattern is entered to the advanced instruction or when
execution of advanced instructions, such as division by zero, has produced any value out of the bit pattern, a user program
execution error will result, turning on special internal relay M8004 and the ERR LED on the CPU module.
Carry and Borrow in Floating-Point Data Processing
When advanced instructions involving floating-point data are executed, special internal relay M8003 (carry and borrow) is updated.
s e[30:23] f[22:0]
31 30 23 22 0
Single Storage Format
23-bit fraction 8-bit biased exponent
Sign bit (0: positive, 1: negative)
Value Exponent field e Fraction field f Representation in WindLDR
±0 e=0 f=0 0.0
Denormal numbers e=0 f ≠ 0 -1.175495E-38 to 1.175495E-38
Normal numbers 0<e<255 Arbitrary
-3.38 to -1.175495E-38
1.175495E-38 to 3.38
± ∞ (± infinities)
e=255
f=0 INF
NaNs (Not a number values) f ≠ 0 NAN
M8003 Execution Result Value
1 Overflow (out of the range between –3.402823  10
38
and 3.402823  10
38
)
1 0 Not zero (within the range between –1.175495  10
–38
and 1.175495  10
–38
)
0 0 Zero
0

0
–1.175495

10
–38
M8003 1 1
1.175495

10
–38
0 –3.402823

10
38
0
Execution Result
1
Overflow
0 1
3.402823

10
38
Overflow
Not Zero