04-01-2016, 11:40 PM
(04-01-2016, 11:20 PM)TSO Wrote: Is there a link somewhere where I can learn about this CCA technology. It wasn't something that existed (or at least isn't an acronym I can figure out) last time I was here.
CCA (Carry Cancel Adder) was invented by MagicalGentleman. It uses comparators to simultaneously compute all carry lines (unlike CLA / CLE which creates each carry line separately). Comparators have a subtract mode where you can subtract the side input from the back input, which is the core mechanism of CCA.
The adder is split into two lines, carry line and cancel line. The carry line is the OR of all the generates (A AND B / A XNOR B) and the cancel line is the OR of all the inverted propagates (A NOR B). Each carry is generated from carry line - cancel line, which means that a carry is only generated if a generate is present and if all inverted propagates in between it and the current bit are false (presence of a propagate or another generate). This allows for a very compact vertical adder, the smallest designed by Embizone. I don't know where you could find a better explanation of the carry logic, but you may want to try Magic's forum threads or their YouTube channel (I believe they posted a video about CCA).