My question is "what is the need of using auxiliary carry?" I mean 'AC' flag is set when D3 generates a carry. Then why not different flags for D2 or D4?

Why suddenly we are treating D3 carry in a special way?


It is used for BCD arithmetic. Each decimal requires 4 bits.

  • $\begingroup$ Thank you so much. Obvious logic and I missed the point. Thanks for the answer. $\endgroup$ – Demietra95 May 31 '15 at 13:56

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