SECTION 1
GENERAL DESCRIPTION
The MC68881 and MC68882 floating-point coprocessors (FPCP) both fully implement the
IEEE Standard for Binary Floating-Point Arithmetic
(ANSI-IEEE Std 754-1985) for use with
the Freescale M68000 Family of microprocessors. The coprocessors are both implemented
in VLSl technology to give system designers the highest possible functionality in a phys-
ically small device. The MC68882 provides an increased level of performance in a copro-
cessor that is fully compatible and physically interchangeable with the MC68881.
Intended primarily for use as coprocessors to the MC68020/MC68030 32-bit microprocessor
unit (MPU), the MC68881 and MC68882 provide a logical extension to the main processing
unit integer data processing capabilities. These coprocessors provide a very high perform-
ance floating-point arithmetic unit and a set of floating-point data registers utilized in a
manner that is analogous to the use of the integer data registers. The MC68881/MC68882
instruction set, a natural extension of all earlier members of the M68000 Family, supports
all of the addressing modes of the host MPU. Due to the flexible bus interface of the M68000
Family, the MC68881 or MC68882 can be used with any of the MPU devices of the family
and may also be used
as a peripheral
to other processors.
The major features of the MC68881 and MC68882 are:
• Eight general-purpose floating-point data registers, each supporting a full 80-bit ex-
tended precision real
data
format (a 64-bit mantissa plus a sign bit, and a 15-bit signed
exponent).
• A
67-bit arithmetic unit to allow very fast calculations, with intermediate precision
greater than the extended precision format.
• A 67-bit barrel shifter for high-speed shifting operations (for normalizing, etc.).
•
Forty-six instructions, including 35 arithmetic operations.
• Full conformance to the ANSI-IEEE 754-1985 standard, including all requirements and
suggestions.
• Support of functions not defined by the IEEE standard, including a full set of trigon-
ometric and transcendental functions.
• Seven data formats: byte, word, and long word integers; single, double, and extended
precision real numbers; and packed binary coded decimal string real numbers.
• Twenty-two constants available in the on-chip ROM, including ~r, e, and powers of 10.
• Virtual memory/machine operations.
• Efficient mechanisms for exception processing, context switches, and interrupt han-
dling.
• Fully concurrent instruction execution with the main processor.
• Use with any host processor, on an 8-, 16-, or 32-bit data bus.
MC68881/MC68882 USER'S MANUAL
FREESCALE
1-1
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