AMD Am186 Series, Instruction Set, Page: 288 / 320

Instruction Set 4-248
XLAT Translate Table Index to Component XLAT
XLATB Translate Table Index to Byte
What It Does
XLAT translates the offset index of a byte stored in memory to the value of that byte.
Syntax
Description
XLAT changes the AL register from the table index to the table entry. The AL register should
be an unsigned index into a table addressed by the DS:BX register pair.
The operand allows for the possibility of a segment override, but the instruction uses the
contents of the BX register even if it differs from the offset of the operand. Load the operand
offset into the BX register—and the table index into AL—before executing XLAT.
Use the no-operand form, XLATB, if the table referenced by BX resides in the DS segment.
Operation It Performs
Flag Settings After Instruction
Form Opcode Description
Clocks
Am186 Am188
XLAT
m8
D7 Set AL to memory byte segment:[BX+unsigned AL] 11 15
XLATB D7 Set AL to memory byte DS:[BX +unsigned AL] 11 15
Use this form to override the default source segment
(DS), and to have the assembler type-check your
operand. In this form, base is segment:[BX].
XLAT base
XLATB
To translate AL to the value of the byte
located at offset [BX][AL] in the segment
specified in DS, use this form.
/* extend index */
temp = 0x00FF & AL;
/* store indexed component in AL */
AL = DS:[BX + temp];
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Processor Status
Flags Register
reserved
OF DF IF TF SF ZF AF PF CF
? = undefined; – = unchanged
– – – – – – res – res – res –