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Does parallel binary adder actually make additions in each position simultaneously? I have read various sources and they all have this description relating to the parallel binary adder: "The additions in each position are taking place at the same time."

However, in my opinion, lefter positions have to wait for the results of the righter ones because of carry bits.

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Am I thinking right? I really appreciate any helps!!

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  • \$\begingroup\$ "The additions in each position are taking place at the same time." Seems like it is referring to look ahead carry adder. While the schematic that you have provided works the way you have described. \$\endgroup\$ – Transistor Mar 31 '18 at 3:32
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Each bit is added simultaneously. However, the bit sum will not be accurate until the carry in has propagated from it's lower order neighbor. Each carry will propagate in turn. Therefore, you must wait until the last carry has arrived at the MSB and been included in the sum of that MSB (S4 in your example) before you consider the result S1..S4 to be stable. At this time, you can latch or otherwise evaluate the sum.

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