Chapter 3. Program DataGFK-2950C February 2018 533.9.2 Floating Point NumbersFloating point numbers are stored in one of two IEEE 754 standard formats that uses adjacent 16-bitwords: 32-bit single precision or 64-bit double precision.The REAL data type represents single precision floating point numbers. The LREAL data typerepresents double precision floating point numbers. REAL and LREAL variables are typically used tostore data from analog I/O devices, calculated values, and constants.Types of Floating Point VariablesData Type Precision and RangeREAL Limited to 6 or 7 significant digits, with a range of approximately±1.401298x10-45 through ±3.402823x1038.LREAL Limited to 17 significant digits, with a range of approximately±2.2250738585072020x10-308 to ±1.7976931348623157x10308.Note: The programming software allows 32-bit and 64-bit arguments (DWORD, DINT, REAL, andLREAL) to be placed in discrete memories such as %I, %M, and %R in the PACSystems target.This is not allowed on Series 90-70 targets. (Note that any bit reference address that ispassed to a non-bit parameter must be byte-aligned. This is the same as the Series 90-70CPU.)Internal Format of REAL Numbers16 132 178-bit exponent1-bit sign (Bit 32)Bits 1-16Bits 17-3223-bit mantissaRegister use by a single floating point number is diagrammed below. For example, if the floating pointnumber occupies registers R5 and R6, R5 is the least significant register and R6 is the mostsignificant register.Bits 17-32Most Significant RegisterLeast Significant BitMost Significant Bit32 1716 1Bits 1-16Least Significant RegisterLeast Significant BitMost Significant BitInternal Format of LREAL Numbers111-bit exponent1-bit sign (Bit 64)Bits 1-16Bits 49-6452-bit mantissaBits 17-32Bits 33-48
