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

2. 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,5H
MOV BL,10H
MUL BL ; CF=0

3. Example 1
Program to multiply two 8 bit numbers.

4. 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.

5. DIV/IDIV Instructions (Example)
Divide 8003h by 100h, using 16-bit operands:
MOV DX,0 ; clear dividend, high
MOV AX,8003H ; dividend, low
MOV CX,100H ; divisor
DIV CX ; AX = 0080h, DX = 3

6. 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.

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

8. 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. SS
stack
segment
ESP
memory

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

10. 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

11. 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

12. OUTDEC Procedure
PGM9_1.ASM

13. INDEC Procedure
PGM9_3.ASM

14. INDEC Procedure
PGM9_3.ASM

15. INDEC / OUTDEC Procedures MAIN PROGRAM