Program to find 2’s complement of a 16-bit number

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Q. Write an 8085 program and draw a flowchart to find 2’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 INX H 23 Increment H-L pair to find 2’s complement.
200A SHLD 3002H 22 Store the result at address 3002H.
200B     02  
200C     30  
200D HLT   76 HALT

Output

Before Execution:

3000H:    12H

3001H:     05H

After Execution:

3002H:     EEH

3003H:     FAH

Program Explanation

  1. This program finds the 2’s complement of a 16-bit number stored in memory locations 3000H-3001H.
  2. There is no direct way to find 2’s complement of the 16-bit number. Therefore, this can be accomplished by finding the 1’s complement of two 8-bit numbers and then incrementing it to get 2’s complement.
  3. Let us assume that the operand stored at memory locations 3000H-3001H is 12H-05H.
  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. H-L pair is incremented to get 2’s complement.
  12. Now, the final result is in H-L pair.
  13. The result is stored from H-L pair to memory locations 3002H-3003H.
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