s10_01.htm

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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Section 10.1</TITLE></HEAD><BODY><B>up:</B> <A HREF="c10.htm">Chapter 10 -- Initialization</A><BR><B>prev:</B> <A HREF="c10.htm">Chapter 10 -- Initialization</A><BR> <B>next:</B> <A HREF="s10_02.htm">10.2  Software Initialization for Real-Address Mode</A><P><HR><P><H1>10.1  Processor State After Reset</H1>The contents of EAX depend upon the results of the power-up self test. Theself-test may be requested externally by assertion of BUSY# at the end ofRESET. The EAX register holds zero if the 80386 passed the test. A nonzerovalue in EAX after self-test indicates that the particular 80386 unit isfaulty. If the self-test is not requested, the contents of EAX after RESETis undefined.<P>DX holds a component identifier and revision number after RESET as <A HREF="#fig10-1">Figure 10-1</A>  illustrates. DH contains 3, which indicates an 80386 component. DLcontains a unique identifier of the revision level.<P>Control register zero (CR0) contains the values shown in <A HREF="#fig10-2">Figure 10-2</A>  . TheET bit of CR0 is set if an 80387 is present in the configuration (accordingto the state of the ERROR# pin after RESET). If ET is reset, theconfiguration either contains an 80287 or does not contain a coprocessor. Asoftware test is required to distinguish between these latter twopossibilities.<P>The remaining registers and flags are set as follows:<PRE>   EFLAGS             =00000002H   IP                 =0000FFF0H   CS selector        =000H   DS selector        =0000H   ES selector        =0000H   SS selector        =0000H   FS selector        =0000H   GS selector        =0000H   IDTR:              base    =0              limit   =03FFH</PRE>All registers not mentioned above are undefined.<P>These settings imply that the processor begins in real-address mode withinterrupts disabled.<P><A NAME="fig10-1"><IMG align=center SRC="fig10-1.gif" border=0><HR><A NAME="fig10-2"><IMG align=center SRC="fig10-2.gif" border=0><P><HR><P><B>up:</B> <A HREF="c10.htm">Chapter 10 -- Initialization</A><BR><B>prev:</B> <A HREF="c10.htm">Chapter 10 -- Initialization</A><BR><B>next:</B> <A HREF="s10_02.htm">10.2  Software Initialization for Real-Address Mode</A></BODY>

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