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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Section 15.7</TITLE></HEAD><BODY><B>up:</B> <A HREF="c15.htm">Chapter 15 -- Virtual 8086 Mode</A><BR><B>prev:</B> <A HREF="s15_06.htm">15.6 Differences From 8086</A><BR><B>next:</B> <A HREF="c16.htm">Chapter 16 -- Mixing 16-Bit and 32 Bit Code</A><P><HR><P><H1>15.7 Differences From 80286 Real-Address Mode</H1>The 80286 processor implements the bus lock function differently than the80386. This fact may or may not be apparent to 8086 programs, depending onhow the V86 monitor handles the <A HREF="LOCK.htm">LOCK</A> prefix. <A HREF="LOCK.htm">LOCK</A>ed instructions aresensitive to IOPL; therefore, software designers can choose to emulate itsfunction. If, however, 8086 programs are allowed to execute <A HREF="LOCK.htm">LOCK</A> directly,programs that use forms of memory locking specific to the 8086 may notexecute properly when transported to a specific application of the 80386.<P>The <A HREF="LOCK.htm">LOCK</A> prefix and its corresponding output signal should only be used toprevent other bus masters from interrupting a data movement operation. <A HREF="LOCK.htm">LOCK</A>may only be used with the following 80386 instructions when they modifymemory. An undefined-opcode exception results from using <A HREF="LOCK.htm">LOCK</A> before anyother instruction.<UL><LI> Bit test and change: <A HREF="BTS.htm">BTS</A>, <A HREF="BTR.htm">BTR</A>, <A HREF="BTC.htm">BTC</A>.<LI> Exchange: <A HREF="XCHG.htm">XCHG</A>.<LI> One-operand arithmetic and logical: <A HREF="INC.htm">INC</A>, <A HREF="DEC.htm">DEC</A>, <A HREF="NOT.htm">NOT</A>, and <A HREF="NEG.htm">NEG</A>.<LI> Two-operand arithmetic and logical: <A HREF="ADD.htm">ADD</A>, <A HREF="ADC.htm">ADC</A>, <A HREF="SUB.htm">SUB</A>, <A HREF="SBB.htm">SBB</A>, <A HREF="AND.htm">AND</A>, <A HREF="OR.htm">OR</A>, <A HREF="XOR.htm">XOR</A>.</UL>A locked instruction is guaranteed to lock only the area of memory definedby the destination operand, but may lock a larger memory area. For example,typical 8086 and 80286 configurations lock the entire physical memory space.With the 80386, the defined area of memory is guaranteed to be lockedagainst access by a processor executing a locked instruction on exactly thesame memory area, i.e., an operand with identical starting address andidentical length.<P><HR><P><B>up:</B> <A HREF="c15.htm">Chapter 15 -- Virtual 8086 Mode</A><BR><B>prev:</B> <A HREF="s15_06.htm">15.6 Differences From 8086</A><BR><B>next:</B> <A HREF="c16.htm">Chapter 16 -- Mixing 16-Bit and 32 Bit Code</A></BODY>⌨️ 快捷键说明
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