Program to find 1’s complement of an 16-bit number

Q. Write a program and draw a flow chart to find 1’s complement of a 16-bit number.(8085 Microprocessor Program)

Flowchart/Algorithm

Program

Address Mnemonics Operand Opcode Comments
2000 LHLD 3000H 2A Load H-L pair with data from 3000H.
2001     00  
2002     30  
2003 MOV  A, L 7D Move the lower-order from reg. L to reg. A.
2004 CMA 2F Complement accumulator.
2005  MOV  L, A 6F  Move the result from reg. A to reg. L.
2006  MOV  A, H 7C  Move the higher-order from reg. H to reg. A.
2007 CMA   2F Complement accumulator.
2008 MOV H, A 67 Move the result from reg. A to reg. H.
2009 SHLD 3002H 22 Store the result at address 3002H.
200A 02
200B 30
200C HLT 76 HALT

Output

Before Execution:

3000H:    45H

3001H:     6AH

After Execution:

3002H:     7AH

3003H:     95H

Program Explanation

  1. This program finds the 1’s complement of a 16-bit number stored in memory 3000H-3001H.
  2. There is no direct way to find 1’s complement of the 16-bit number. Therefore, this can be accomplished by finding the 1’s complement of two 8-bit numbers.
  3. Let us assume that the operand stored at memory locations 3000H-3001H is 45H-6AH.
  4. The operand is loaded into H-L pair from memory locations 3000H-3001H.
  5. The lower-order is moved from register L to accumulator.
  6. Its complement is found by using CMA instruction.
  7. The result obtained is moved back to register L.
  8. Then, the higher-order is moved from register H to accumulator.
  9. Its complement is found by using CMA instruction.
  10. The result obtained is moved back to register H.
  11. Now, the final result is in H-L pair.
  12. The result is stored from H-L pair to memory locations 3002H-3003H.

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