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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Section 3.9</TITLE></HEAD><BODY><B>up:</B> <A HREF="c03.htm">Chapter 3 -- Applications Instruction Set</A><BR><B>prev:</B> <A HREF="s03_08.htm">3.8 Flag Control Instructions</A><BR><B>next:</B> <A HREF="s03_10.htm">3.10 Segment Register Instructions</A><P><HR><P><H1>3.9 Coprocessor Interface Instructions</H1>A numerics coprocessor (e.g., the 80387 or 80287) provides an extension tothe instruction set of the base architecture. The coprocessor extends theinstruction set of the base architecture to support high-precision integerand floating-point calculations. This extended instruction set includesarithmetic, comparison, transcendental, and data transfer instructions. Thecoprocessor also contains a set of useful constants to enhance the speed ofnumeric calculations.<P>A program contains instructions for the coprocessor in line with theinstructions for the CPU. The system executes these instructions in the sameorder as they appear in the instruction stream. The coprocessor operatesconcurrently with the CPU to provide maximum throughput for numericcalculations.<P>The 80386 also has features to support emulation of the numericscoprocessor when the coprocessor is absent. The software emulation of thecoprocessor is transparent to application software but requires more timefor execution . Refer to <A HREF="c11.htm">Chapter 11</A> for more information on coprocessoremulation.<P>ESC (Escape) is a 5-bit sequence that begins the opcodes that identifyfloating point numeric instructions. The ESC pattern tells the 80386 to sendthe opcode and addresses of operands to the numerics coprocessor. Thenumerics coprocessor uses the escape instructions to performhigh-performance, high-precision floating point arithmetic that conforms tothe IEEE floating point standard 754.<P><A HREF="WAIT.htm">WAIT</A> (Wait) is an 80386 instruction that suspends program execution untilthe 80386 CPU detects that the BUSY pin is inactive. This conditionindicates that the coprocessor has completed its processing task and thatthe CPU may obtain the results.<P><A NAME="fig3-23"><IMG align=center SRC="fig3-23.gif" border=0><P><HR><P><B>up:</B> <A HREF="c03.htm">Chapter 3 -- Applications Instruction Set</A><BR><B>prev:</B> <A HREF="s03_08.htm">3.8 Flag Control Instructions</A><BR><B>next:</B> <A HREF="s03_10.htm">3.10 Segment Register Instructions</A></BODY>⌨️ 快捷键说明
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