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Chapter 17 -- 80386 Instruction Set
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XLAT/XLATB -- Table Look-up Translation
D7 XLAT m8 5 Set AL to memory byte DS:[(E)BX + unsigned AL]
D7 XLATB 5 Set AL to memory byte DS:[(E)BX + unsigned AL]
Operation
IF AddressSize = 16
THEN
AL := (BX + ZeroExtend(AL))
ELSE (* AddressSize = 32 *)
AL := (EBX + ZeroExtend(AL));
FI;
Description
XLAT changes the AL register from the table index to the table entry. AL
should be the unsigned index into a table addressed by DS:BX (for an
address-size attribute of 16 bits) or DS:EBX (for an address-size attribute
of 32 bits).
The operand to XLAT allows for the possibility of a segment override. XLAT
uses the contents of BX even if they differ from the offset of the operand.
The offset of the operand should have been moved intoBX/EBX with a previous
instruction.
The no-operand form, XLATB, can be used if the BX/EBX table will always
reside in the DS segment.
Flags Affected
None
Protected Mode Exceptions
#GP(0) for an illegal memory operand effective address in the CS, DS, ES,
FS, or GS segments; #SS(0) for an illegal address in the SS segment;
#PF(fault-code) for a page fault
Real Address Mode Exceptions
Interrupt 13 if any part of the operand would lie outside of the effective
address space from 0 to 0FFFFH
Virtual 8086 Mode Exceptions
Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault
up:
Chapter 17 -- 80386 Instruction Set
prev: XCHG Exchange Register/Memory with Register
next: XOR Logical Exclusive OR