Intel 80287 Processor Extension Synchronization Instructions, Numeric Data Processor Instructions

BASIC INSTRUCTION SET

A program contains instructions for the NPX in line with the instructions for the CPU. The system executes these instructions in the same order as they appear in the instruction stream. The NPX operates concurrently with the CPU to provide maximum throughput for numeric calculations.

The software emulation of the NPX is transparent to application software but requires more time for execution.

3.12.1 Processor Extension Synchronization Instructions

Escape and wait instructions allow a processor extension such as the 80287 NPX to obtain instructions and data from the system bus and to wait for the NPX to return a result.

ESC (Escape) identifies floating point numeric instructions and allows the 80286 to send the opcode to the NPX or to transfer a memory operand to the NPX. The 80287 NPX uses the Escape instructions to perform high-performance, high-precision floating point arithmetic that conforms to the IEEE float- ing point standard 754.

Example: ESC 6, ARRAY [SIlo The CPU sends the escape opcode 6 and the location of the array pointed to by SI to the NPX.

WAIT (Wait) suspends program execution until the 80286 CPU detects a signal on the BUSY pin. In a configuration that includes a numeric processor extension, the NPX activates the BUSY pin to signal that it has completed its processing task and that the CPU may obtain the results.

Example: WAIT

3.12.2 Numeric Data Processor Instructions

This section describes the categories of instructions available with Numeric Data Processor systems that include a Numeric Processor Extension or a software emulation of this processor extension.

3.12.2.1 ARITHMETIC INSTRUCTIONS

The extended instruction set includes not only the four arithmetic operations (add, subtract, multiply, and divide), but also subtract-reversed and divide-reversed instructions. The arithmetic functions include square root, modulus, absolute value, integer part, change sign, scale exponent, and extract exponerit instructions.

3.12.2.2 COMPARISON INSTRUCTIONS

The comparison operations are the compare, examine, and test instructions. Special forms of the compare

instruction can optimize algoriihms by ailuwiug cOiilpafisuii5 of binary integer:; ....ith real r.:um.ber~ in

memory.

3_12.2.3 TRANSCENDENTAL INSTRUCTIONS

The instructions in this group perform the otherwise time-consuming calculations for all common trigonometric, inverse trigonometric, hyperbolic, inverse hyperbolic, logarithmic, and exponential functions. The transcendental instructions include tangent, arctangent, 2 x - I, Y . log2X, and Y. log2 (X+l).

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