Mitsubishi Electric MELSEC-Q Structured Programming Manual page 129

FXCPU Structured Programming Manual
[Device & Common]
Decimal floating point (real number) (scientific notation)
Because binary floating point (real number) is difficult to understand for users, it can be converted into
decimal floating point (real number). But the PLC executes internal operations using binary floating point (real
number) in any case.
Decimal floating point (real number) is handled by a pair of data registers having consecutive 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 decimal floating point as shown below.
Data can be written to D0 and D1 by the MOV instruction.
Decimal floating point (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
two's complement respectively.
The mantissa D0 does not allow "100", for example. In the case of "100", it is handled as "1000 × 10
The decimal floating point (real number) handles the following range:
- Minimum absolute value 1175 × 10
- Maximum absolute value 3402 × 10
Number of significant figures
The number of significant figures of decimal floating point is approximately "4" when expressed in the decimal
notation.
Decimal floating point handles the above range.
Decimal floating point (real number) is valid in the following instructions:
- Conversion from binary floating point (real number) into decimal floating point (real number): DEBCD
- Conversion from decimal floating point (real number) into binary floating point (real number): DEBIN
3 How to Specify Devices and Constants in Instructions
3.1 Numeric Values Handled in PLCs (Octal, Decimal, Hexadecimal and Real Numbers)
Mantissa D0=± (1,000 to 9,999) or 0
Exponent D1=-41 to +35
-41
35
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