My Nand2Tetris Journey #2 - Building Basic Chips And ALU
What I Built HalfAdder, FullAdder, Add16, Inc16, And ALU. How I Solved Like when I built logic gates, I started with analyzing truth table of HalfAdder , FullAdder . HalfAdder was really easy. After looking at the truth table, I could map the sum and carry outputs to logic gates pretty quickly. FullAdder was also not hard since it's really similar to HalfAdder except that it can add 3 bits. I realized that I could build it by combining some chips and logic gates I had already made instead of designing everything again from scratch. Once I finished building them, I was also able to build Add16 . At first, I had no idea how to sum all the 16 bits. But I soon realized that I could build a 16-bit adder by combining the smaller adders I had already built and passing carry information to the next bit. It looks not beautiful, but still works. And about Inc16 , it's basically add exactly 1(0000000000000001) . So I could easily build it using Add16 . (But I did something weird at first.. check the Reflection below) ALU was the core part of project 2. Once I realized that Mux can be used as if , I could make proper outputs using logic gates. ALU is also a combination of logic gates and chips, after all. What I Learned How to build basic chips using logic gates and already-built chips Why I should reuse the chips for another chip(check the Reflection section below) Mux can be used like if How to use bit slicing and fan-out in HDL and why it's important Reflection Before I started this part, I didn't know two things: I could use bit slicing and true , false for each bit. So when I first tried to build Inc16 , it looked really weird, since I calculated all the bits one by one. It's not logically wrong. But not beautiful either. I was not sure if it was right or not. Then I realized that I already built Add16 . But I had no idea how I could use it to add exactly 1(0000000000000001) . After googling, I realized that I could use bit slicing like Python's list slicing and construct