PPT Slide

4 – Combinational Logic Design Examples

© 1996 Gaetano Borriello

2s complement (cont'd)

• If N is a positive number, then the negative of N ( its 2s complement or N* ) isN* = 2n – N

  • example: 2s complement of 7
  • example: 2s complement of –7
  • shortcut: 2s complement = bit-wise complement + 1
    • 0111 -> 1000 + 1 -> 1001 (representation of -7)
    • 1001 -> 0110 + 1 -> 0111 (representation of 7)

23

2 = 10000

7 = 0111

1001 = repr. of –7

4

2 = 10000

–7 = 1001

0111 = repr. of 7

4

subtract

subtract

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