8085 program to subtract two BCD numbers

Problem – Write an assembly language program in 8085 microprocessor to subtract two 8 bit BCD numbers.

Example –

Algorithm –

1. Load the data from address 2051 in A
2. Move the data from A to C
3. Move the data 99 in A
4. Subtract the contents of registers A and C
5. Increment the content of A by 1
6. Move the data from A to B
7. Load the data from address 2050 in A
8. Add the contents of A and C and adjust it in BCD format by using DAA instruction
9. Store the result at memory address 3050
10. Stop

Program –

MEMORY ADDRESS	MNEMONICS	COMMENT
2000	LDA 2051	A <- 2051
2003	MOV C, A	C <- A
2004	MVI A 99	A <- 99
2006	SUB C	A = A – C
2007	INR A	A = A + 1
2008	MOV B, A	B <- A
2009	LDA 2050	A <- 2050
200C	ADD B	A = A + B
200D	DAA	Convert the hexadecimal value to BCD value
200E	STA 3050	3050 <- A
2011	HLT	Stop

Explanation –

1. LDA 2051 is used to load the data from address 2051 in A.
2. MOV C, A is used to move the data from A to C.
3. MVI A 99 is used to move the data to register A.
4. SUB C is used to subtract the contents of registers A and C.
5. INR A is used to increment the content of A by 1.
6. MOV B, A is used to move the data from A to B.
7. LDA 2050 is used to load the data from address 2050 in A.
8. ADD B is used to add the contents of registers A and B.
9. DAA is used to convert the hexadecimal value in Accumulator to BCD value.
10. STA 3050 is used to store the contents of A to 3050.
11. HLT is used end the program.

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