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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Opcode SGDT</TITLE></HEAD><BODY><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="SETcc.htm"> SETcc Byte Set on Condition</A><BR><B>next:</B><A HREF="SHLD.htm"> SHLD Double Precision Shift Left</A><P><HR><P><H1>SGDT/SIDT -- Store Global/Interrupt Descriptor Table Register</H1><PRE>Opcode Instruction Clocks Description0F 01 /0 SGDT m 9 Store GDTR to m0F 01 /1 SIDT m 9 Store IDTR to m</PRE><H2>Operation</H2><PRE>DEST := 48-bit BASE/LIMIT register contents;</PRE><H2>Description</H2>SGDT/SIDT copies the contents of the descriptor table register the sixbytes of memory indicated by the operand. The LIMIT field of theregister is assigned to the first word at the effective address. If theoperand-size attribute is 32 bits, the next three bytes are assigned theBASE field of the register, and the fourth byte is written with zero. Thelast byte is undefined. Otherwise, if the operand-size attribute is 16bits, the next four bytes are assigned the 32-bit BASE field of theregister.<P>SGDT and SIDT are used only in operating system software; they arenot used in application programs.<H2>Flags Affected</H2>None<H2>Protected Mode Exceptions</H2>Interrupt 6 if the destination operand is a register; #GP(0) if thedestination is in a nonwritable segment; #GP(0) for an illegal memoryoperand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) foran illegal address in the SS segment; #PF(fault-code) for a page fault<H2>Real Address Mode Exceptions</H2>Interrupt 6 if the destination operand is a register; Interrupt 13 if anypart of the operand would lie outside of the effective address space from0 to 0FFFFH<H2>Virtual 8086 Mode Exceptions</H2>Same exceptions as in Real Address Mode; #PF(fault-code) for a pagefault<H2>Compatability Note</H2>The 16-bit forms of the SGDT/SIDT instructions are compatible withthe 80286, if the value in the upper eight bits is not referenced. The80286 stores 1's in these upper bits, whereas the 80386 stores 0's if theoperand-size attribute is 16 bits. These bits were specified as undefinedby the SGDT/SIDT instructions in the iAPX 286 Programmer'sReference Manual.<P><HR><P><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="SETcc.htm"> SETcc Byte Set on Condition</A><BR><B>next:</B><A HREF="SHLD.htm"> SHLD Double Precision Shift Left</A></BODY>?? 快捷鍵說明
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