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2's Complement of 2Byte Number

This program will work out the 2's Complement of a 2 Byte Number. As Microprocessor can perform 8 bits at a time in Accumulator, so we follow the foloowing Algo

  1. Fetch the 2 Byte Number in a Register Pair
  2. Bring Least Significant Byte of the Number from last Register into A (Accumulator)
  3. Make Complement of A and add 1
  4. Store back the Updated LSByte into its source Register
  5. Bring MSByte of the Number from another Register into A
  6. Make Complement of A and add 1 if carry was genetrated at the time of LSByte opeartion
  7. Store back the Updated MSByte into its source Register
  8. Store the Result to a Memory location

Suppose, Argument Number is stored in Location 1000H and 1001H Memory Location and store the value in 2000H and 2001H Memory Locations.
Memory LocationHex CodeLabelMnemonicsComment
3050
3051
3052		2A
00
10		START:LHLD 1000H;Load the HL Register Pair with the content of Memory Location 1000H and 1001H
30537DMOV A, L;Move the Content of L to A (Accumulator)
30542FCMA;Make Complement of Least Significant Byte of the Number
3055
3056		C6>
01		ADI 01H;Add 1 with LSByte of the number to make 2's complement
30576FMOV L, A;Send Back the Updated Data to L
30587CMOV A, H;Bring the MSByte of the Number in A
30592FCMA;Make 1's Complement of MSByte of Number
305A
305B
305C		D2
5F
30		JNC NOCARRY;If Carry was not generated in LSByte Operation, Jump into NOCARY Section
305D
305E		C6
01		ADI 01H;Make 2's Complement of MSByte if carry was generated in LSByte operation
305F67NOCARRY:MOV H, A;Send back the Updated MSByte to H
3060
3061
3062		22
00
20		SHLD 2000H;Store the Result from HL to the Memory Location 2000H
306376HLT;End of Program

If you want to use INR A to add 1 with 1's Complement to make 2's Complement, you should use at the time of increamention of MSByte not at LSByte. Because INR do not update CY(Carry) Flag if carry is generated.

You can use the following algo also to do the same.

  1. Fetch the 2 Byte Number in a Register Pair
  2. Bring the Least Significant Byte into A
  3. Make Complement of A
  4. Store back to Register
  5. Bring the MSByte into A
  6. Make Complement of A
  7. Store Back to Register
  8. increase this Resgister pair using INX Rp
  9. Store the Result in Memory
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