8085 program to count total even numbers in series of 10 numbers

Program – Write an assembly language program in 8085 microprocessor to count even numbers in a series of 10 numbers. 

Example –

Assumption – Ten 8-bit numbers are stored from starting memory location 2050. Value of count is stored at memory location 3050. 

Algorithm –

1. Initialize register H with 20 and register L with 4F so that indirect memory points to memory location 204F.
2. Initialize register C with 00 and register D with 0A.
3. Increment indirect memory by 1.
4. Store value of M in accumulator A.
5. Check whether the content in A is even or odd by performing AND operation of A with 01.
6. If content of A is 00 after AND operation then the number scanned was even, If so then increment C by 01 else if content of A is 01 after AND operation then number scanned was odd, If so then decrements D by 01.
7. Check if zero flag is not set i.e. ZF = 0 then jump to step 3 otherwise store value of C at memory location 3050.

Program (Using ANI Instruction) –

MEMORY ADDRESS	MNEMONICS	COMMENT
2000	LXI H 204F	H <- 20, L <- 4F
2003	MVI C, 00	C <- 00
2005	MVI D, 0A	D <- 0A
2007	INX H	M <- M + 01
2008	MOV A, M	A <- M
2009	ANI 01	A <- A (AND) 01
200B	JNZ 200F	Jump if ZF = 0
200E	INR C	C <- C + 01
200F	DCR D	D <- D – 01
2010	JNZ 2007	Jump if ZF = 0
2013	MOV A, C	A <- C
2014	STA 3050	M[3050] <- A
2017	HLT	END

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

1. LXI H 204F: assign 20 to H and 4F to L.
2. MVI C, 00: assign 00 to C.
3. MVI D, 0A: assign 0A to D.
4. INX H: increment indirect memory location M by 01.
5. MOV A, M: move content of M to A.
6. ANI 01: perform AND operation of A with 01 and store the result in A.
7. JNZ 200F: jump if ZF = 0 to memory location 200F.
8. INR C: increment C by 01.
9. DCR D: decrements D by 01.
10. JNZ 2007: jump if ZF = 0 to memory location 2007.
11. MOV A, C: moves the content of C to A.
12. STA 3050: store the content of A to memory location 3050.
13. HLT: stops executing the program and halts any further execution.

Alternative Approach (Using Rotate Instructions):

For a given set of numbers, If the Least Significant Bit(LSB) of each number’s Binary representation is 1, then the given number is assured to be an Odd Number.

But if the Least Significant Bit (LSB) of each number’s binary representation is 0, then the given number is assured to be an Even Number.

Hence, here we will use Rotate Instructions of 8085 Microprocessor. i.e. RAR Instruction (Rotate Accumulator Right involving Carry flag in Rotation).

If we rotate the given binary number in the right direction by 1-bit then we will get the carry a flag as Zero or One.

If we get Carry Flag = 1, then the given number is ODD, Otherwise EVEN.

MEMORY ADDRESS	Symbols	COMMENT
2000	LXI H,204FH	Load HL Pair with Previous location of 2050H , H <- 20, L <- 4F
2003	MVI C,00H	For storing count of Even Numbers [C]=0H
2005	MVI D,0AH	For series of 10 numbers we have stored array size as [D]=10
2007	INX H	Increment memory pointer pointed by HL pair
2008	MOV A,M	Move Content of memory location 2050H into Accumulator A. {[A] <- [M]}
2009	RAR	Rotate Accumulator Right with Carry .
200B	JC 200F	After rotating if Carry Flag=1 then we can say that given number is ODD, So we just need to move to next element nothing to do extra here.
200E	INR C	if we found that Carry Flag=0 then we can say that given Number is EVEN, So we need to increment our count by 1.Hence INR C will happen for all subsequent conditions.
200F	DCR D	Now if we have found out whether given number is ODD/EVEN then we need to decrement array size because here size is 10 and we need to decrement till 0.
2010	JNZ 2007	Until [D]=0 we have to decrement D and move to next memory location and take input of 10 numbers (This is looping Structure.)
2013	MOV A,C	(After whole looping is over)Transfer/Copy Contents of register C which contains total number of even numbers into Accumulator.
2014	STA 3050H	Store Accumulator Content which contains count of Even Numbers to Memory Location 3050H as required in Question
2017	HLT	End of a Program Execution