Assembly Language – Lab 5MUL, DIV, Stack, INDEC, OUTDEC

MUL/IMUL Instructions• The MUL (Multiply) instruction handles unsigned data and the IMUL

(Integer Multiply) handles signed data.

• Example - 8-bit unsigned multiplication (5 * 10h):

MOV AL,5HMOV BL,10HMUL BL ; CF=0

Example 1• Program to multiply two 8 bit numbers.

DIV/IDIV Instructions• The division operation generates two elements - a quotient and a remainder.• The DIV instruction is used or unsigned data and the IDIV is used or signed

data.

DIV/IDIV Instructions (Example)• Divide 8003h by 100h, using 16-bit operands:

MOV DX,0 ; clear dividend, highMOV AX,8003H ; dividend, lowMOV CX,100H ; divisorDIV CX ; AX = 0080h, DX = 3

CBW, CWD Instructions• CBW (convert byte to word) extends AL into AH− If bit 7 of AL is a 1, the instruction will place FF in AH.− If bit 7 of AL is a 0, the instruction will place 00 in AH.

• CWD (convert word to doubleword) extends AX into DX− If bit 15 of AX is a 1, the instruction will place FFFF in DX.− If bit 15 of AX is a 0, the instruction will place 0000 in DX.

• NOTE: Use this instruction only with signed arithmetic.

Example 2• Divide 16 bit numbers by an 8 bit numbers.

PUSH/POP Instructions (Stack)• LIFO (Last-In, First-Out) data structure, items are added and removed from

one end of the structure.• To ‘push’ an item means to insert it, and to ‘pop’ an item means to remove it.• Managed by the CPU, using two registers:

• SS (stack segment)• ESP (stack pointer): point to the top of the stack.

stacksegment

SS

ESP

memory

Example 3• Program to swap the content of AX and BX.

Procedures• The procedure start with the name of the procedure followed by PROC

(reserved word), at the end of procedure write RET, also the procedure name followed with ENDP.

• To invoke a procedure, the CALL instruction is used.

name PROC..RET

name ENDP

INDEC / OUTDEC Procedures• Procedures used to read and print decimal data. • INDEC

Code of INDEC exist in file PGM9_3.ASM• OUTDEC

Code of OUTDEC exist in file PGM9_1.ASM

• Include the two files using INCLUDE directive. • Syntax: INCLUDE C:\emu8086\MySource/PGM9_3.ASM

INCLUDE C:\emu8086\MySource/PGM9_1.ASM

OUTDEC ProcedurePGM9_1.ASM

INDEC ProcedurePGM9_3.ASM

INDEC ProcedurePGM9_3.ASM

INDEC / OUTDEC ProceduresMAIN PROGRAM