80386 Programmer's Reference Manual -- Opcode XLAT

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]


IF AddressSize = 16
   AL := (BX + ZeroExtend(AL))
ELSE (* AddressSize = 32 *)
   AL := (EBX + ZeroExtend(AL));


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


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

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