3 ms·
This took the place of a full adder, which has three input bits. (In other words, it was a single adder with three inputs, not a 3-bit-wide adder.) I don't see
by kens 7y ago
This took the place of a full adder, which has three input bits. (In other words, it was a single adder with three inputs, not a 3-bit-wide adder.) I don't see how 5 bits would help.
- kragen 7y agoA carry in, two bits from each addend, and three bits out. Halves your carry-chain length in a ripple adder, and the DAC and adder parts of the circuit are a doddle; even an R–2R DAC is plenty, even at many MHz. But then you need a 3-bit ADC for the output. They didn't know about lookahead carry yet, did they? As I said below, the Chinese abacus uses it, but the relevance of that may not have been apparent at the time.