8085 program to check whether both the nibbles of 8 bit number are equal or not

Problem – Write an assembly language program in 8085 microprocessor to check whether both the nibbles of 8 bit number are equal or not. If nibbles are equal then store 00 in memory location 3050 otherwise store FF in memory location 3050.

Example –

Assumption – Number, to check for similar nibbles is stored at memory location 2050.

Algorithm –

1. Load the content of memory location 2050 in A.
2. Moves the content of A in B.
3. Mask the lower nibble and store it in register C.
4. Move the content of B in A.
5. Mask the higher order nibble and store it in A.
6. Reverse the content of A by using RLC instruction 4 times.
7. Compare the contents of A and C by help of CMP instruction. Update the flags of 8085.
8. Now store FF if ZF = 0 otherwise store 00 if ZF = 1.
9. Store the final result in memory location 3050.

Program –

MEMORY ADDRESS	MNEMONICS	COMMENT
2000	LDA 2050	A <- M[2050]
2003	MOV B, A	B <- A
2004	ANI 0F	A <- A (AND) 0F
2006	MOV C, A	C <- A
2007	MOV A, B	A <- B
2008	ANI F0	A <- A (AND) 0F
200A	RLC	Rotate content of A left by one bit without carry
200B	RLC	Rotate content of A left by one bit without carry
200C	RLC	Rotate content of A left by one bit without carry
200D	RLC	Rotate content of A left by one bit without carry
200E	CMP C	A – C
200F	JZ 2018	Jump if ZF = 1
2013	MVI A, FF	A <- FF
2015	JMP 201A	Jump to memory location 201A
2018	MVI A, 00	A <- 00
201A	STA 3050	M[3050] <- A
201D	HLT	END

Explanation – Registers A, B, C are used for general purpose.

1. LDA 2050: load the content of memory location 2050 in accumulator A.
2. MOV B, A: moves the content of A in register B.
3. ANI 0F: performs AND operation in contents of A and 0F. Store the result in A.
4. MOV C, A: moves the content of A in register C.
5. MOV A, B: moves the content of B in A.
6. ANI F0: performs AND operation in contents of A and F0. Store the result in A.
7. RLC: rotates content of A left by one bit without carry. Use the instruction 4 times to reverse the number.
8. CMP C: compares the content of A and C. Update the flags of 8085 accordingly.
9. JZ 2018: jump to memory location 2018 if zero flag is set.
10. MVI A, FF: assign FF to A.
11. JMP 201A: jump to memory location 201A.
12. MVI A, 00: assign 00 to A.
13. STA 3050: store the content of A in memory location 3050.
14. HLT: stops executing the program and halts any further execution.

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