Homebuilt TTL and transistor CPUs - wierd logic

instead Personally, I prefer negabinary (base -2). It uses 2-state signals, but the column values are powers of -2 : . . .16, -8, 4, -2, 1

Every postive and negative integer has a unique representation. The adder works (obvuiously) with +ve and -ve numbers. Shift-and-and multiplication works, as does shift-and-subtract division (using negabinary adders/subtractors). To negate a number, shift it left one bit and add it to the origiginal number (this is multiplying by 11, which is -1 of course) negabinary decimal 1100 -4 1101 -3 0010 -2 0011 -1 0000 0 0001 1 0110 2 0111 3 0100 4 Note that numbers of a odd-number of bits length (ingoring leading zeros) are +ve, those of an even number of bits are -ve Years ago I built a 4-bit negabinary adder. The full adder stage has 3 outputs (sum, carry, carry+1) since you have to be able to add 1+1 giveing 110 and therefore has 4 inputs (2 bits to sum, carry in from last stage, carry in to last-but-one stage). -tony