AIM: Write a Program to generate Factorial of a number

Objective:

To understand the concept of multiplication using direct MUL instruction in 8086. To understand how to use 16-bit results

To analyze the process and the result

System Requirement : 

8086 Trainer Kit with Key Board

Setting up the Trainer Kit:

1. Ensure that standard IBM PC/AT system keyboard is connected
2. System is Powered ON
3. Student has a handy opcode table for programming
4. Use data Address as :
   1. For Program Code

segment address : 1000       Offset address : 0200

1. For Data

segment address  : 0000      Offset address : 1300

Result               : from offset 130A

Flowchart:

Algorithm to find the factorial of a number–

1. Input the Number whose factorial is to be find and Store that Number in CL Register (Condition for LOOP Instruction)
2. Initialize AL=01, AH=00
3. Multiply CL with AL until CL become Zero(0) using LOOP Instruction
4. Copy the content of AL to Destination Address
5. Copy the content of AH to Destination Address + 01
6. Stop Execution

Explanation of the code for factorial of a number

Code Segment	Op-Code	Mnemonic	Explanation
1300: 0200	BE 0013	MOV SI, 1300h	; set source index
1300: 0203	BF 0A 13	MOV DI, 130Ah	; set destination index
1300: 0206	8A 0C	MOV CL, [SI]	; CL loaded with 8-bit FROM 1300
1300: 0208	B0 01	MOV AL, 01	; AL is initialized to 01h
1300: 020A	B4 00	MOV AH, 00	; AH register initialized to 0000
1300: 020C	F6 E1	Back: MUL CL	; Multiply  AX
1300: 020E	FE C9	DEC CL	; Decrement multiplier by 1
1300: 0210	75 FA	JNZ Back	; Go To back label
1300: 0212	88 05	MOV [DI], AL	; store low part of result
1300: 0214	47	INC DI	; increment destination index
1300: 0215	88 25	MOV [DI], AH	; Store high byte of result
1300: 0217	F4	HLT	; stops executing  program

Execution of the Program

Address Map for DATA and RESULT

	Data Segment Address	DATA
Number whose factorial is needed	Segment  : Offset: 0000 : 1300	05
Result	Segment  : Offset: 0000 : 130A and 0000 : 130B	78 00 (0078)hex = decimal (120)

Executing The Program

	Key Pressed/Action	Display on LCD
	Press G  from Keyboard	BURST
	Press Enter	Segm_Adr
0000	Press Enter	Ofst
0200	Press Enter	Wait Cmd_Wrd=
Do not press the Reset Key; Check the result by using Sub_Mir Command

Verification of Result

TRY		Address	High Byte	Low Byte
1st	Number	0000:1300	xx
	Factorial	Value->
		Address->	0000:130B	0000:130A
2nd	Number	0000:1300	xx
	Factorial	Value->
		Address->	0000:130B	0000:130A
3rd	Number	0000:1300	xx
	Factorial	Value->
		Address->	0000:130B	0000:130A

Viva Question

Q.1: How do you use MUL instruction for 8-bit multiplication?

Answer:

Syntax ;           MUL CL for 8-bit;           Result in AX

When we multiply two 8-bit number, result will be a 16-bit value. For example if we multiply two 8-bit numbers available in AL and CL the execution of MUL CL will result in AX <- AL*CL

We store content of AL at low address and AH at high address

Q.2: How do you use MUL instruction for 16-bit multiplication?

Answer:

Syntax :           MUL CX for 16-bit value Result in DX:AX

When we multiply two 16-bit number, result will be a 32-bit value. Execution of MUL CX will result in DX : AX  <- AX*CX

We store result at four memory locations