8085 program to add 2-BCD numbers

Problem – Write a program to add 2-BCD numbers where starting address is 2000 and the numbers is stored at 2500 and 2501 memory addresses and store sum into 2502 and carry into 2503 memory address.

Example –

Algorithm –

1. Load 00H in a register (for carry)
2. Load content from memory into register pair
3. Move content from L register to accumulator
4. Add content of H register with accumulator
5. Add 06H if sum is greater than 9 or Auxillary Carry is not zero
6. If carry flag is not equal to 1, go to step 8
7. Increment carry register by 1
8. Store content of accumulator into memory
9. Move content from carry register to accumulator
10. Store content of accumulator into memory
11. Stop

Program –

Memory	Mnemonics	Operands	Comment
2000	MVI	C, 00H	[C] <- 00H, carry
2002	LHLD	[2500]	[H-L] <- [2500]
2005	MOV	A, L	[A] <- [L]
2006	ADD	H	[A] <- [A] + [H]
2007	DAA		Add 06 if sum > 9 or AC = 1
2008	JNC	200C	Jump if no carry
200B	INR	C	[C] <- [C] + 1
200C	STA	[2502]	[A] -> [2502], sum
200F	MOV	A, C	[A] <- [C]
2010	STA	[2503]	[A] -> [2503], carry
2013	HLT		Stop

Explanation – Registers A, C, H, L are used for general purpose

1. MVI is used to move data immediately into any of registers (2 Byte)
2. LHLD is used to load register pair direct using 16-bit address (3 Byte instruction)
3. MOV is used to transfer the data from memory to accumulator (1 Byte)
4. ADD is used to add accumulator with any of register (1 Byte instruction)
5. STA is used to store data from accumulator into memory address (3 Byte instruction)
6. DAA is used to check if sum > 9 or AC = 1 add 06 (1 Byte instruction)
7. JNC is used jump if no carry to given memory location (3 Byte instruction)
8. INR is used to increase given register by 1 (1 Byte instruction)
9. HLT is used to halt the program

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