Mitsubishi Electric MELSEC FX3U Programming Manual page 163

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
Scientific notation (real number)
Because binary floating point (real number) is difficult to understand for users, it can be converted into
scientific notation (real number). But internal operations are executed using binary floating point (real
number).
Scientific notation (real number) is handled by a pair of data registers having serial device numbers. Different
from binary floating point (real number), a data register having a smaller device number handles the mantissa
part, and the other data register having a larger device number handles the exponent part.
For example, when data registers D1 and D0 are used, they handle scientific notation as shown below. Data
can be written to D0 and D1 by MOV instruction.
Scientific notation (real number) = [Mantissa D0] × 10 [Exponent D1]
The most significant bit of D0 and D1 specifies the positive or negative sign respectively, and is handled as
the complement of 2 respectively.
The mantissa D0 does not allow "100", for example. In the case of "100", it is handled as "1000 × 10
The scientific notation (real number) range is as follows:
- Minimum absolute value: 1175 × 10
- Maximum absolute value: 3402 × 10
Number of significant figures
The number of significant figures of scientific notation is approximately 4 when expressed in decimal. The
scientific notation range is as described above.
Scientific notation (real number) is valid in the following instructions:
- Conversion from binary floating point (real number) into scientific notation (real number): FNC118
([D]EBCD)
- Conversion from scientific notation (real number) into binary floating point (real number): FNC119
([D]EBIN)
5 How to Specify Devices and Constants to Instructions
5.1 Numeric Values Handled in PLCs (Octal, Decimal, Hexadecimal and Real Numbers)
Mantissa D0 = ± (1000 to 9999) or 0
Exponent D1 = −41 to +35
−41
35
1
2
3
−1
".
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5
6
7
8
9
10
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