8085 program to multiply two 8 bit numbers using logical instructions

Prerequisite – Logical instructions in 8085 microprocessor Problem – Write a assembly language program multiply two 8 bit numbers and store the result at memory address 3050 in 8085 microprocessor. Example – The value of accumulator(A) after using RLC instruction is:

A = 2n*A

Where n = number of times RLC instruction is used. Assumptions – Assume that the first number is stored at register B, and second number is stored at register C. And the result must not have any carry. Algorithm –

1. Assign the value 05 to register B
2. Assign the value 04 to register C
3. Move the content of B in A
4. Rotate accumulator left without carry
5. Rotate accumulator left without carry
6. Store the content of accumulator at memory address 3050
7. Halt of the program

Program –

MEMORY ADDRESS	MNEMONICS	COMMENTS
2000	MVI B 05	B <- 05
2002	MVI C 04	C <- 04
2004	MOV A, B	A <- B
2005	RLC	rotate the content of A without carry
2006	RLC	rotate the content of A without carry
2007	STA 3050	3050 <- A
200A	HLT	End of the program

Explanation –

1. MVI B 05: assign the value 05 to B register.
2. MVI C 04: assign the value 04 to C register.
3. MOV A, B: move the content of register B to register A.
4. RLC: rotate the content of accumulator left without carry.
5. RLC: rotate the content of accumulator left without carry.
6. STA 3050: store the content of register A at memory location 3050
7. HLT: stops the execution of the program.

Advantages:

• The program is simple and easy to understand since it only uses a few instructions.
  
• The program uses only logical instructions to perform the multiplication operation, which reduces the number of registers required.
  
• The program produces accurate results since it performs a series of bitwise operations to calculate the product.
  

Disadvantages:

• The program is computationally intensive and time-consuming since it requires several instructions to perform the multiplication operation.
  
• The program is not very efficient in terms of memory usage since it requires several registers to store the operands and intermediate results.
  
• The program is not very scalable since it requires a large number of iterations to multiply large numbers, which may cause overflow or underflow conditions.
  
• The program does not handle overflow or underflow conditions, which may occur if the product of the two numbers is greater than 255.
  
• The program does not provide any error checking or reporting mechanism, which may make it difficult to identify errors or faults in the program.