Explain the following instructions with an example for each: (i) XLAT (ii) AND (iii) RCR (iv) DAA (v) AAS

(i) XLAT (Translate):

This instruction is used for table lookups. It takes the value in AL (the accumulator register) as an offset into a table and replaces the value in AL with the byte at the effective address.


MOV AL, 2      ; AL contains the offset
MOV BX, OFFSET Table ; BX points to the start of the table
XLAT           ; Replace AL with the byte at Table+2

(ii) AND (Logical AND):

This bitwise AND operation performs the logical AND between each pair of corresponding bits of the two operands. The result is stored in the destination operand.


MOV AX, 5      ; Binary: 0000 0101
AND AX, 3      ; Binary: 0000 0011
; After AND operation, AX will be: 0000 0001 (1 in decimal)

(iii) RCR (Rotate through Carry Right):

This instruction rotates the bits in the specified operand to the right through the carry flag. The carry flag is included in the rotation.


MOV AX, 8      ; Binary: 0000 1000
RCR AX, 1      ; Rotate AX right through carry by 1 bit
; After RCR operation, AX will be: 1000 0100 (carry will be set to 0)

(iv) DAA (Decimal Adjust Accumulator):

This instruction adjusts the contents of the AL register after an addition operation in packed decimal (BCD) arithmetic.


MOV AL, 90 ; AL contains unpacked BCD (9 in tens place, 0 in units place)
ADD AL, 25 ; Add 25 to AL (BCD addition)
DAA ; Adjust AL to correct BCD representation
; After DAA operation, AL will be: 15 (1 in tens place, 5 in units place)

(v) AAS (ASCII Adjust for Subtraction):

This instruction adjusts the result in the AL register after a subtraction operation in ASCII-coded decimal arithmetic.


MOV AL, '7'    ; AL contains ASCII representation of the digit 7
SUB AL, 3      ; Subtract 3 from AL (ASCII subtraction)
AAS            ; Adjust AL to correct ASCII representation
; After AAS operation, AL will be: '4' (ASCII representation of the digit 4)