80C186EC/80C188EC Microprocessor User's Manual

MATH COPROCESSING
14.3 THE 80C187 MATH COPROCESSOR
The 80C187’s high performance is due to its 80-bit internal architecture. It contains three units:
a Floating Point Unit, a Data Interface and Control Unit and a Bus Control Logic Unit. The foundation
of the Floating Point Unit is an 8-element register file, which can be used either as individually
addressable registers or as a register stack. The register file allows storage of
intermediate results in the 80-bit format. The Floating Point Unit operates under supervision of
the Data Interface and Control Unit. The Bus Control Logic Unit maintains handshaking and
communications with the host microprocessor. The 80C187 has built-in exception handling.
The 80C187 executes code written for the Intel387 DX and Intel387 SX math coprocessors.
The 80C187 conforms to ANSI/IEEE Standard 754-1985.
14.3.1 80C187 Instruction Set
80C187 instructions fall into six functional groups: data transfer, arithmetic, comparison, transcendental,
constant and processor control. Typical 80C187 instructions accept one or two operands
and produce a single result. Operands are usually located in memory or the 80C187 stack.
Some operands are predefined; for example, FSQRT always takes the square root of the number
in the top stack element. Other instructions allow or require the programmer to specify the operand(s)
explicitly along with the instruction mnemonic. Still other instructions accept one explicit
operand and one implicit operand (usually the top stack element).
As with the basic (non-numerics) instruction set, there are two types of operands for coprocessor
instructions, source and destination. Instruction execution does not alter a source operand. Even
when an instruction converts the source operand from one format to another (for example, real to
integer), the coprocessor performs the conversion in a work area to preserve the source operand.
A destination operand differs from a source operand because the 80C187 can alter the register
when it receives the result of the operation. For most destination operands, the coprocessor usually
replaces the destinations with results.
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