Nand2Tetris
, ,
Source
Edit
History

Project 3: Sequential Chips

Catalogue
  1. 1. The Chips to implement
    1. 1.1. 1-Bit Register Chip
    2. 1.2. 16-Bit Register
    3. 1.3. 8-Register Chip
    4. 1.4. RAM64, RAM512, RAM4K,RAM16K
    5. 1.5. Program Counter
  2. 2. Some Questions
  3. 3. While Doing It
  4. 4. Reference

​ We are going to implement 8 chips in this project.

The Chips to implement

1-Bit Register Chip

Tip: It can be built from a DFF and a multiplexor.

16-Bit Register

Tip: A little bit different wiring from the last one.

8-Register Chip

This is the first RAM device consisting of 8 registers. Here is its API:

1
2
3
4
CHIP RAM8 {
	IN in[16], load, address[3];
	OUT out[16];
}

Tips:

  1. We need to feed the in value to all the 8 registers simultaneously.
  2. Then use the Mux or DeMux chips to select the one to operate.

RAM64, RAM512, RAM4K,RAM16K

Tips:

As we started the last RAM8, we can stack the small RAM chip to larger ones, grouping them layer by layer.

Think about the address input as consisting of 2 fields: one to select the RAM, the other to select the register.

Program Counter

Tip: It can be built from a register, an incrementor and other taught gates.

Some Questions

Q. Why there are 2 folders a/ and b/ in Project 3 directory?

A. The larger RAMs, like RAM16K, are built from smaller ones down to the Bit Register, so it will involves a huge recursion. This will be too much for a humble simulator to handle. Therefore, we are supposed to use the built-in Java implementations, which makes it faster and smoother.

Q. We take the Flip Flop as a black box in this course. How is it implemented in real?

A. The core is 2 NAND Gates connected in a loop. A change in a moment can decide the output in the future.

How DFF remembers data

Above shows how gate maintains “memory”. Of course the outer layer is necessary for the DFF functionality.

While Doing It

  • HDL is a description language not a programming language. It is OK to input a new pin name, which appears in the line below, to implement the circle between gates.

Reference