Experiment-3: Write a program to perform: i. Subtraction of two 8 bit numbers without borrows. ii. Subtraction of two 8 bit numbers with borrows.

Objective:

To understand the assembly program

To draw flowchart for subtraction of two numbers

To develop the assembly program for subtraction

To analyse the program and interpret errors and result

Requirement:

Operating System – Windows, Linux

• 8085 Simulator

ALGORITHM

Data variable

Algorithm:

• Load source (X) address in HL pair
• Load source (Y) address in DE pair
• Load Accumulator (A) from memory i.e [HL]
• Swap HL and DE pair HL ßàDE
• Load register B from memory [HL]
• Subtract A-B
• Save result in register C
• Increment HL
• Swap HL with DE HL  ßàDE
• Increment HL
• Load accumulator from memory address 4201 [HL]
• Swap HL and DE
• Load register B from memory
• Subtract with borrow
• Increment HL to save the result
• Save register C (least significant result) at 4205 [HL] ß C
• Increment HL now 4206
• Save most significant digit of result in memory 4206 [HL] ß A
• stop

Program in assembly with OPCODEs

Result:

Viva Questions:

Que-1: How is subtraction performed in computer.

Ans:

Subtraction is performed by using 2’s complement arithmetic.

Que-2: What are the commands available in 8085 microprocessor for performing subtraction

Ans:

1. SUB    –  Subtraction
2. SBB   – subtraction with borrow