Q. Explain XLAT instruction with help of example?

Let's presume a table of hexadecimal characters signifying all 16 hexadecimal digits in table:

HEXA      DB      '0123456789ABCDEF'

The table comprises the ASCII code of every hexadecimal digit:

(All value in hexadecimal)

If we place 0Ah in AL with the thought of converting it to ASCII we have to set BX to offset of HEXA and invoke XLAT.  You need not specify table name with XLAT hence it is implicitly passed by setting BX to HEXA table offset. This instruction would do the subsequent operations:

It will first add AL to BX producing an effective address which points to eleventh entry in the HEXA table.

Content of this entry is now moved to AL register which means 41h is moved to AL. 

Or we can say in other words, XLAT sets AL to 41h since this value is located at HEXA table offset 0Ah. Please consider that 41h is the ASCII code for hex digit A. The subsequent sequence of instructions will accomplish this:

MOV AL, 0Ah    ; index value

MOV BX, OFFSET HEXA; offset of the table HEXA

XLAT     

The above tasks can be executed without XLAT instruction however it will need a long series of instructions like:

MOV AL, 0Ah                                   ; index value

MOV   BX, OFFSET HEXA             ; offset of the table HEXA

PUSH BX                                           ; save the offset

ADD BL, AL                                     ; add index value to table

                                                                        ; HEXA offset

MOV   AL, [BX]                                ; retrieve the entry

POP    BX                                           ; restore BX