8085 program to find nth power of a number

Problem – Write an assembly language code for calculating the nth power of a number using 8085 microprocessor.

Example –

Input : Base=>02H
        Exponent=>03H  
Output :08H 

In 8085 microprocessor, no direct instruction exists to multiply two numbers, so multiplication is done by repeated addition as 4*4 is equivalent to 4+4+4+4(ie 4 times).
Load 02H(base) to register B and 03H(exponent) to register C -> set D register to 02H -> Add 02H B(ie 2) times -> D register now contains 04H -> Add 04H B(ie 2) times -> D register now contains 08H -> Output is 08H.

Algorithm –

1. Load the base into register B and exponent into register C.
2. To start multiplication set D to 01H.
3. Jump to step 7.
4. Decrements C.
5. Jump to step 3 till value of C>0.
6. Take memory pointer to next location and store result.
7. Load E with contents of B and clear accumulator.
8. Repeatedly add contents of D to accumulator E times.
9. Store accumulator content to D.
10. Go to step 4.

Program –

Address	Label	Mnemonic	Comment
2000H	Base		Data Byte for base
2001H	Exponent		Data Byte for exponent
2002H	Result		Result of factorial
2003H		LXI H, 2000H	Load data from memory
2006H		MOV B, M	Load base to B register
2007H		INX H	Increment memory
2008H		MOV C, M	Load exponent to C register
2009H		MVI D, 01H	Set D register to 1
200BH	POWER_LOOP	CALL MULTIPLY	Subroutine call for multiplication
200EH		DCR C	Decrement C
200FH		JNZ POWER_LOOP	Call power_loop till C becomes 0
2012H		INX H	Increment memory
2013H		MOV M, D	Store result in memory
2014H		HLT	Halt
2100H	MULTIPLY	MOV E, B	Transfer contents of B to E
2101H		MVI A, 00H	Clear accumulator to store result
2103H	MULTIPLYLOOP	ADD D	Add contents of D to A
2104H		DCR E	Decrement E
2105H		JNZ MULTIPLYLOOP	Repeated addition
2108H		MOV D, A	Transfer contents of A to D
2109H		RET	Return from subroutine

Explanation –

1. Set register B with base and register C with exponent.
2. Set register D with base by calling MULTIPLY subroutine one time.
3. Decrement C and add D to itself B times by calling MULTIPLY subroutine.
4. Repeat the above step till C reaches 0 and then exit the program.
5. The result is obtained in D register which is stored in memory

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