8085 program to count the number of ones in contents of register B

Problem – Write an assembly language program to count the number of ones in contents of register B and store the result at memory location 3050.

Example –

Algorithm –

• Convert the decimal number in Accumulator to its binary equivalent
• Rotate the digits of the binary number right without carry
• Apply a loop till count is not zero to change the values of D register and count
• Copy the value of D register to accumulator and store the result

Program –

MEMORY ADDRESS	MNEMONICS	COMMENTS
2000	MVI B 75	B ← 75
2002	MVI C 08	C ← 75
2004	MVI D 00	D ← 00
2006	MOV A, B	A ← B
2007	RRC	Rotate right without carry
2008	JNC 200C	Jump if Not Carry
200B	INR D	D ← D+1
200C	DCR C	C ← C-1
200D	JNZ 2007	Jump if Not Zero
2010	MOV A, D	A ← D
2011	STA 3050	A → 3050
2014	HLT	Stops execution

Explanation –

1. MVI B 75 moves 75 decimal number into B register
2. MVI C 08 moves 08 decimal number into C register, which is taken as counter as the number is of 8 bites
3. MVI D 00 moves 00 number into d register
4. MOV A, B moves the contents of B register into A (accumulator) register
5. RRC rotates the contents of A (which is 75 with binary equivalent 01110101) right
   

6. JNC 200C jumps to 200C address and perform the instructions written there if the carry flag is not zero
7. INR D increases the value of D register by adding one to its contents
8. DCR C decreases the value of C register by subtracting one from its contents
9. JNZ 2007 jumps to 2007 address and perform the instructions written there if the zero flag is not zero
10. MOV A, D moves the contents of B register into A register
11. STA 3050 store the contents of A at 3050 memory location
12. HLT stops execution