Homebuilt TTL and transistor CPUs - wierd logic
Tony Duell
ard at p850ug1.demon.co.uk
Tue Jan 24 18:50:15 CST 2006
> Balanced trinary means place values go up by three each, but 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
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