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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Section 10.2</TITLE></HEAD><BODY><B>up:</B> <A HREF="c10.htm">Chapter 10 -- Initialization</A><BR><B>prev:</B> <A HREF="s10_01.htm">10.1 Processor State After Reset</A><BR><B>next:</B> <A HREF="s10_03.htm">10.3 Switching to Protected Mode</A><P><HR><P><H1>10.2 Software Initialization for Real-Address Mode</H1>In real-address mode a few structures must be initialized before a programcan take advantage of all the features available in this mode.<P><H2>10.2.1 Stack</H2>No instructions that use the stack can be used until the stack-segmentregister (SS) has been loaded. SS must point to an area in RAM.<P><H2>10.2.2 Interrupt Table</H2>The initial state of the 80386 leaves interrupts disabled; however, theprocessor will still attempt to access the interrupt table if an exceptionor nonmaskable interrupt (NMI) occurs. Initialization software should takeone of the following actions:<UL><LI> Change the limit value in the IDTR to zero. This will cause a shutdownif an exception or nonmaskable interrupt occurs. (Refer to the 80386Hardware Reference Manual to see how shutdown is signalled externally.)<LI> Put pointers to valid interrupt handlers in all positions of theinterrupt table that might be used by exceptions or interrupts.<LI> Change the IDTR to point to a valid interrupt table.</UL><H2>10.2.3 First Instructions</H2>After RESET, address lines A{31-20} are automatically asserted forinstruction fetches. This fact, together with the initial values of CS:IP,causes instruction execution to begin at physical address FFFFFFF0H. Near(intrasegment) forms of control transfer instructions may be used to passcontrol to other addresses in the upper 64K bytes of the address space. Thefirst far (intersegment) <A HREF="JMP.htm">JMP</A> or <A HREF="CALL.htm">CALL</A> instruction causes A{31-20} to droplow, and the 80386 continues executing instructions in the lower onemegabyte of physical memory. This automatic assertion of address linesA{31-20} allows systems designers to use a ROM at the high end ofthe address space to initialize the system.<P><HR><P><B>up:</B> <A HREF="c10.htm">Chapter 10 -- Initialization</A><BR><B>prev:</B> <A HREF="s10_01.htm">10.1 Processor State After Reset</A><BR><B>next:</B> <A HREF="s10_03.htm">10.3 Switching to Protected Mode</A></BODY>⌨️ 快捷键说明
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