Consider a base 16 adder. How can I modify the adder so that it can perform a base 8 addition?

I expect this question will appear in my exam tomorrow; if anyone can give me a hint or a solution, I'd be grateful. I've tried searching the net and my textbook to get some insight, but nothing is clicking.

my textbook digital design 5th morris mano

  • $\begingroup$ Perhaps it helps if you think about it in decimal. Suppose you have a machine that can add two 2-digit numbers. How can you use it to add two 1-digit numbers? $\endgroup$ – Yuval Filmus Dec 30 '14 at 6:41

Assumptions/Statements: A base 16 adder: an adder that adds two 4-bit binary numbers I1 and I2 and outputs the 4-bit result R and a carry bit C

To use as a base 8 adder (as above) discard the Most Significant Bit from both I1 and I2 (i.e. ground/zero them). Now your inputs are base-8. From the output discard the Carry bit C it will always be zero. Your new Carry bit will be the Most Significant Bit from result R. Your new result will be the 3 least significant bits from R.

Please check Assumptions/Statements are in accordance to your book!


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