Using LPM_ADD_SUB: Signed Numbers

• MegaWizard Assumes Signed Numbers

• Sign Extend Data Width and Ignore Carry

  • Example: Adding Two 8 Bit Signed Buses
    • Sign extend to 9 Bit and use a 9-bit “SIGNED” LPM_ADD_SUB
    • Use the 9 bit result and ignore the carry out
  • Example: Adding Two 8 Bit Unsigned Buses
    • Set the 9th Bit to zero and use a 9-bit “SIGNED” LPM_ADD_SUB
    • Use the 9 bit result and ignore the carry out

• Use LPM_ADD_SUB to access “UNSIGNED” Numbers.

• ADD_SUB port will increase the design size and reduce speed

If possible use ADD functions with sign extension

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