Working on a new 8 bit ALU!

[Chibill]

Okay so as many of you know I have give up on my item memory as 1.8 will destroy it. So I will start work on an 8 bit ALU but here is the question what are the normal way to make a ALU because many of the ALU's I have build when look at from a real world perceptive would not be an good ALU.

So I am asking you for examples in the form of lists of how I should order or connect the parts and what parts i should have. I might mix and match parts or your list with others.

And this ALU will be made for speed as my last one was a 4 bit one that was a theoretical 9 ticks for adding or subtracting and 6 ticks for logic but i know it could probably not run that fast.

Then my next project will be to make a CPU with both first a 4 bit CPU then a 8 bit one.

[greatgamer34]

6 ops needed,
1)OR
2)CIN
3)Invert A
4) Invert B
5)Flood Carry
6)Right Shift

every logical function could be made with this such as, AND= Invert A,B, OR, Flood Carry. XOR= invert b, flood carry.

[Chibill]

Okay ,But I have no idea how to use the Flood Carry thing. Unless you mean just turn on all carries And I don't believe that this works very well with CLE adders which I think ,If i remember right,are faster the Insta-Carry adders.

[greatgamer34]

Okay ,But I have no idea how to use the Flood Carry thing. Unless you mean just turn on all carries And I don't believe that this works very well with CLE adders which I think ,If i remember right,are faster the Insta-Carry adders.

Actually it works with all adders. For CLE the horizontal bars out of all of the torches are your carries, flood those and that is flood carry. CLE is synced whereas ICA is not. ICA could be instant but most are like 3.5 ticks. A fast Standard CLE is 4 tick, a CLE with inverted output could be 3 ticks.

[Chibill]

That is still an improvement over my adder (which is a greatly modified version of one of shrogg's insta-carry to make it a tick fast).

As for the invert should I also have an invert output?

And finally how should I control if it adds or Ors with a Mux? Because I don't really like it when you Add by default because it makes the controls of the full build more complicated.

[greatgamer34]

No invert output, thats what flood carry does.

No muxes because that is slow, U have control lines that toggle what to do. By default you can have the adder do OR where it will just by pass the inputs if thats what you want

[Chibill]

That's the thing I have never used a mux in an ALU so okay. I have used compactor zeroing gates thou.

[EDevil]

Zero'ing is something the redstone community used to do with ALU's. But when you start hooking your ALU up to some dual read registers, you can also just say that you don't want to read from Reg A or B, meaning an input of 0.

[Chibill]

I mean to select my output.

---

And gamer what do you mean by the or because to make and have a separate IR gate won't work right? P.s. I have never made a Adder base ALU.

[greatgamer34]

If the ALU by default is set to do OR it wont add 2 numbers. It will just let them pass through. Or you can put a and gate on you inputs and decide if you wanted your iputs to go through depending on the OP.

[Chibill]

I mean you said to and you flood carry invert a
,b and OR but the OR would keep it from being and and right? (P.s. on phone.)

[greatgamer34]

Lol what. To make "AND" you do,
1)Invert A
2)Invert B
3)OR
4)Flood Carry
Just try it, you will see.
The purpose of the "OR" is to prevent a carry to the next bit therefore allowing Bitwise functions!

[Chibill]

That makes to sense at all because the or is sreaprate from the adder. Notice like I said before I have never made this type of alu.

[greatgamer34]

To make OR on an alu, just make it so it cannot generate. AKA flood the AND on your first Xor/xnor/

[Chibill]

I understand none of this... The only type of ALU I have ever made was the type with the different gates in it that does not take an a odd input system to get the logic gates.

[EDevil]

Look Chi, i made stuff for you!

Here's what Great means when he says flood the first XOR;



Now, how can we do this in MC? Well with our good old RCA its pretty simple.


Colorscheme ( Orange: first XOR, Yellow: AND gates, Blue: Carry, Cobblestone: preventing signal interference, Red: 2nd XOR)

First we need to deactivate our carry line (for those who think they know it better, yes only OR function will suffice in this adder, and cut carry wont be necessary. However, in some adders just OR isn't enough.). To do that, i placed pistons on top of my carry line to prevent it going into the 2nd XOR. This line is color coded with Cyan wool.


The next thing is making our first XOR into an OR. I choose to do it by placing an extra control wire with torches above the first XOR. If the torch is on, there's no way that the torch in the middle of the XOR will turn on, meaning that you can now toggle between ADD and OR.



And this would be our final result. Our old adder with 2 extra control wires, Cut carry (cyan wool) and OR (purple wire).



And if we have these inputs and flip both our new functions on...


We'll have our OR output

[Chibill]

Thanks! Now to apply this to CLE adders.

[greatgamer34]

The Same way. On the First Xnor you have your "AND" & you have your "NOR". THe OR line is as simple as powering onto the "NAND" part of the "AND" gate. Flood Carry is simply flooding all of the carries(which are the horizontal bars with torches leading into them, they go into the final XNOR).

[Chibill]

I follow you tut on that! :-)

And i am making my own 1.5 tick shifter.

[greatgamer34]

I follow you tut on that! :-)

And i am making my own 1.5 tick shifter.

My shifter is a 1 tick throughput with a 1 tick shift

[Chibill]

Its 2 ticks by the time i fix the weird inverted output for you inverted ram.
And I like mine... Don't want to copy every thing now do i..

[Chibill]

I have a problem with my ALU I try to do and and it is shifted on bit to towards the carry out

[Chibill]

Now done except for the shift. Might just use greats shift and then its an other alu of his but yeah this is basicly done.