Four bit adder: Difference between revisions

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This design can be realized using four [[wp:Adder_(electronics)#Full_adder|1-bit full adder]]s.

Each of these 1-bit full adders can be built with two [[wp:Adder_(electronics)#Half_adder|half adder]]s and an ''or'' [[wp:Logic gate|gate]]. ~~Finally a half adder can be made using a ''xor'' gate and an ''and'' gate.~~

Each of these 1-bit full adders can be built with two [[wp:Adder_(electronics)#Half_adder|half adder]]s and an   ''or''   [[wp:Logic gate|gate]]. ;

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The ''xor'' gate can be made using two ''not''s, two ''and''s and one ''or''.

Finally a half adder can be made using an   ''xor''   gate and an   ''and''   gate.

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'''Not''', '''or''' and '''and''', the only allowed "gates" for the task, can be "imitated" by using the [[Bitwise operations|bitwise operators]] of your language.

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If there is not a ''bit type'' in your language, to be sure that the ''not'' does not "invert" all the other bits of the basic type (e.g. a byte) we are not interested in, you can use an extra ''nand'' (''and'' then ''not'') with the constant 1 on one input.

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The   ''xor''   gate can be made using two   ''not''s,   two   ''and''s   and one   ''or''.

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Instead of optimizing and reducing the number of gates used for the final 4-bit adder, build it in the most straightforward way, ''connecting'' the other "constructive blocks", in turn made of "simpler" and "smaller" ones.

⚫

'''Not''',   '''or'''   and   '''and''',   the only allowed "gates" for the task, can be "imitated" by using the [[Bitwise operations|bitwise operators]] of your language.

⚫

If there is not a ''bit type'' in your language, to be sure that the   ''not''   does not "invert" all the other bits of the basic type   (e.g. a byte)   we are not interested in,   you can use an extra   ''nand''   (''and''   then   ''not'')   with the constant   '''1'''   on one input.

⚫

Instead of optimizing and reducing the number of gates used for the final 4-bit adder,   build it in the most straightforward way,   ''connecting'' the other "constructive blocks",   in turn made of "simpler" and "smaller" ones.

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