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+---- Thread: The CCA - Carry-Cancel Adder (/thread-5493.html)
RE: The CCA - Carry-Cancel Adder - Magic :^) - 06-19-2015
![[Image: dTxHiq0.png]](http://i.imgur.com/dTxHiq0.png)
The pink line that goes in to the third comparator on the blue section is the OR control line.
That comparator when not disabled floods the xor output with an OR signal instead. It does not matter that the XOR is still active, as the only time that an XOR is on is also a time when the OR line is on.
RE: The CCA - Carry-Cancel Adder - Legofreak - 06-21-2015
the simplicity of how you make it OR makes me want to re-think my life choices.
RE: The CCA - Carry-Cancel Adder - Chibill - 08-22-2015
Sorry for the bump. But I am going to try and make a diagonal or horizontal one of this.
RE: The CCA - Carry-Cancel Adder - Magic :^) - 08-22-2015
nice
it's really interesting seeing other people's takes on the design :3
RE: The CCA - Carry-Cancel Adder - CrazyGuy108 - 08-22-2015
Can't wait till 3 tick CCA comes around. Combining the carry logic with the final XOR, according to Yap7, would definitely tie CLE and CCA for fastest adder, making vertical CPUs not such a bad idea.
But still...
#diagonalmasterrace
RE: The CCA - Carry-Cancel Adder - Yap7 - 08-23-2015
My theory is that a 3 ticks CCA is possible if we use some tricks.
The minimum ticks is 3 because there is at least 3 successive components:
1 - The first XOR, a NOR, a AND
2 - The comparator's carry
3 - The last XOR
As the comparator is 1 tick and it exist design for 1 tick XOR, steps 2 and 3 can take 1 ticks each. If we want 3 ticks, we have to make the first step 1 tick too.
There is 3 components:
- The XOR : We can make it 2 ticks because it can be done at the same time as the carry (the output of this XOR is linked to the input of the last XOR)
- The NOR : /(A+B) It's easy to make it 1 ticks
- The AND : /(/A+/B) It need 2 ticks to build an AND gate, that's the problem here.
A way to solve this is to give the illusion of a 3 ticks CCA in a CCA ALU by using the input inverter (either way, what the need of a CCA if it's not for an ALU?). As it can give both inverted and non inverted input within 1 tick, we can use it to take inverted inputs for the AND gate and make it a NOR witch is 1 tick.
So the CCA will have 4 inputs: A,B,/A,/B and the inverter will have 4 outputs. By mixing them, it's possible to have a system inverter+CCA witch is 4 ticks. As the inverter will be 1 ticks, it will be like the CCA is 3 ticks.
So in theory, it is possible to have a 3 ticks CCA inside a CCA ALU, but the design is hard to find as we had to fit 4 inputs inside a very compact space.
RE: The CCA - Carry-Cancel Adder - Don_Manuel_1229 - 08-23-2015
I was studying CCA today. (I'm confident that i can prove that it is a carry look ahead adder).
There is no AND gate, thus no generate line. The AND is implicit in the (A xnor B) nimplies (A nor B) ....along with a lot other calculations happening on the carry-logi comparator.
I Too believe that CCA can be 3 ticks, but i think that the problem is equivalent to making a 1 tick XNOR gate
#Let me know if you want me to post a proof
!
RE: The CCA - Carry-Cancel Adder - Magic :^) - 08-23-2015
yeah i found out about the xnor thing a while ago, that's how there's a 4-wide 4-tick one in existance.
and yeah, the biggest problem in making it 3 tick is making a 1 tick XNOR gate that outputs full signal strength.
also don, if you look back a few pages i have a logisim circuit modelling how CCA behaves, with an array of transistors, or gates, and weighted wires to represent the signal strength being handled by the comparators. It looks very similar to CLA
RE: The CCA - Carry-Cancel Adder - Don_Manuel_1229 - 08-23-2015
(to any future ppl reading this: a full signal strength xnor or a 14signal strength xnor; for 8 bits)
Yeah, I saw the logisim post. I realized it would be more fun if i figured it out (since i know the 4 tick layout by heart). Hex logic ftw! Spend all night on it, basically ~6hrs. I was sad to learn that there is no generate line, only a propagate line and a "pre generate line" (what you call the cancel line), bc it complicates some project i have. Hopefully I'll overcome it!
Hate to sound like a fan-girl... but great stuff, Magic!
RE: The CCA - Carry-Cancel Adder - jxu - 08-24-2015
I'm still not sure what this is (I never took the time to figure out the carry system), but the title reminds me of an old prototype I had on my plot years ago of a carry-skip adder that delivers good performance increases with very limited extra logic. Maybe this is similar, maybe not, but I haven't seen anyone ever develop the idea.