8085 program to reverse 16 bit number

Problem – Write an assembly language program in 8085 microprocessor to reverse 16 bit number.

Example – Assume 16 bit number is stored at memory location 2050 and 2051.

Algorithm –

1. Load contents of memory location 2050 in register L and contents of memory location 2051 in register H
2. Move contents of L in accumulator A
3. Reverse the contents of A by executing RLC instruction 4 times
4. Move the contents of A in L
5. Move the contents of H in A
6. Reverse the contents of A by executing RLC instruction 4 times
7. Move the contents of L in H
8. Move the contents of A in L
9. Store the content of L in memory location 2050 and contents of H in memory location 2051

Program –

MEMORY ADDRESS	MNEMONICS	COMMENT
2000	LHLD 2050	L <- M[2050], H <- M[2051]
2003	MOV A, L	A <- L
2004	RLC	Rotate accumulator content left by 1 bit without carry
2005	RLC	Rotate accumulator content left by 1 bit without carry
2006	RLC	Rotate accumulator content left by 1 bit without carry
2007	RLC	Rotate accumulator content left by 1 bit without carry
2008	MOV L, A	L <- A
2009	MOV A, H	A <- H
200A	RLC	Rotate accumulator content left by 1 bit without carry
200B	RLC	Rotate accumulator content left by 1 bit without carry
200C	RLC	Rotate accumulator content left by 1 bit without carry
200D	RLC	Rotate accumulator content left by 1 bit without carry
200E	MOV H, L	H <- L
200F	MOV L, A	L <- A
2010	SHLD 2050	M[2050] <- L, M[2051] <- H
2013	HLT	END

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

1. LHLD 2050: loads contents of memory location 2050 in L and 2051 in H.
2. MOV A, L: moves content of L in A.
3. RLC: shift the content of A left by one bit without carry. Repeat the current instruction 4 times so that contents of A get reversed.
4. MOV L, A: moves the content of A in L.
5. MOV A, H: moves the content of H in A.
6. RLC: shift the content of A left by one bit without carry. Repeat the current instruction 4 times so that contents of A get reversed.
7. MOV H, L: moves the content of L in H.
8. MOV L, A: moves the content of A in L.
9. SHLD 2050: stores the content of L in 2050 and H in 2051.
10. HLT: stops executing the program and halts any further execution.

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