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Subtract Two 16-bits numbers | 8086 Microprocessor

In this tutorial, we will learn how to find the subtraction of two 16-bits numbers using 8086 Microprocessor? By Ayush Sharma Last updated : May 22, 2023

Problem Statement

Write a program to subtract two 16-bit numbers where starting address is 2000 and the numbers are at 3000 and 3002 memory address and store result into 3004 and 3006 memory address.

Algorithm

1. Load 0000H into CX register (for borrow)
2. Load the data into AX(accumulator) from memory 3000
3. Load the data into BX register from memory 3002
4. Subtract BX with Accumulator AX
5. Jump if no borrow
6. Increment CX by 1
7. Move data from AX(accumulator) to memory 3004
8. Move data from CX register to memory 3006
9. Stop

Program

ADDRESS	MNEMONICS	OPERANDS	COMMENTS
2000	MOV	CX, 0000	[CX] <- 0000
2003	MOV	AX, [3000]	[AX] <- [3000]
2007	MOV	BX, [3002]	[BX] <- [3002]
200B	SUB	AX, BX	[AX] <- [AX] – [BX]
200D	JNC	2010	Jump if no borrow
200F	INC	CX	[CX] <- [CX] + 1
2010	MOV	[3004], AX	[3004] <- [AX]
2014	MOV	[3006], CX	[3006] <- [CX]
2018	HLT		Stop

Explanation

1. MOV is used to load and store data.
2. SUB is used to subtract two numbers where their one number is in accumulator or not.
3. JNC is a 2-bit command which is used to check whether the borrow is generated from accumulator or not.
4. INC is used to increment an register by 1.
5. HLT is used to stop the program.
6. AX is an accumulator which is used to load and store the data.
7. BX, CX is general purpose registers where BX is used for storing second number and CX is used to store borrow.

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