8085 program to swap two 8 bit numbers using Direct addressing mode

Problem – Write a program to swap two 8-bit numbers using direct addressing mode where starting address is 2000 and the first 8-bit number is stored at 3000 and the second 8-bit number is stored at 3001 memory address.

Example –

Algorithm –

1. Load a 8-bit number from memory 3000 into accumulator
2. Move value of accumulator into register H
3. Load a 8-bit number from memory 3001 into accumulator
4. Move value of accumulator into register D
5. Exchange both the register pairs
6. Stop

Program –

Memory	Mnemonics	Operands	Comment
2000	LDA	[3000]	[A] <- [3000]
2003	MOV	H, A	[H] <- [A]
2004	LDA	[3001]	[A] <- [3001]
2007	MOV	D, A	[D] <- [A]
2008	XCHG		[H-L] [D-E]
2009	HLT		Stop

Explanation – Registers A, H, D are used for general purpose.

1. LDA is used to load accumulator direct using 16-bit address (3 Byte instruction)
2. MOV is used to transfer the data (1 Byte instruction)
3. XCHG is used to exchange the data of both the register pair (H-L), (D-E) (1 Byte instruction)
4. HLT is used to halt the program.