# Computer

----------

## Summary

1. [Aims and challenges](#aims-and-challenges)
2. [Architecture choices](#architecture-choices)
3. [Design](#design)
    1. [The instruction set.](#the-instruction-set)

## Aims and challenges

Make a turing complete computer from scratch.

The computer will be composed of :
 - A CPU
 - Some RAM
 - Some ROM

At first every part will be the "industrial" version :
 - The CPU from logic gates.
 - The RAM a [SRAM](https://en.wikipedia.org/wiki/Static_random-access_memory) chip (*[UM61256BK-20](/Documents/Datasheets/UM61256.pdf) from 1993*)
 - The ROM another chip (*[D27C010](/Documents/Datasheets/D27C010-200V10.pdf) from 1986 !*)

Then the aim is to replace them with made from scratch versions.
For the moment only the RAM is meant to be replaced with homemade magnetic core RAM.

**NOT ANY SORTS OF AI WILL BE USED IN THIS PROJECT.**

*Why ?*

People in the 70s got someone on the moon with their brain, and made him come back.
AI is useful for medicine, protein research or other deep research subjects.
I do not need a LLM to understand and make a computer.

## Architecture choices

The computer will be in 8 bits since the RAM and ROM are meant to be in 8 bits.
The CPU will have ports for inputs / outputs, not a north and south bridge.

## Design

The design is inspired of great people hard work :
 - [Ben Eater's 8 bits breadboard computer](https://eater.net/8bit)
 - [Mattbatwings's minecraft computer tutorial](https://youtu.be/hAZEXqWLTmY?si=qgic0b28PMeOPs_l)

The core architecture will be inspired of the legendary [Intel's MCS-51](/Documents/Datasheets/8051.PDF) [microcontroller series](https://en.wikipedia.org/wiki/Intel_MCS-51).

### Core architecture

![Computer diagram.](/Documents/Computer%20diagram.svg)
Made with [Drawio](https://app.diagrams.net/).

### Registers

| Name | Long Name               | Description                  |
| :--: | :---------------------- | :--------------------------- |
|  IR  | Instruction Register    | Running instruction storage. |
|  A   | A Register              | ALU first input register.    |
|  B   | B Register              | ALU second input register.   |
|  MAR | Memory Address Register | RAM heap access address.     |
|  SP  | Stack pointer           | RAM stack access pointer.    |

### The instruction set.

Every instruction is 1 to 3 bytes long.
First is the opcode, and the optionnal 2 bytes are the operands.
Operands can be an data (1B), address (1B), or full address (2B).

These are only real instructions. Pseudoinstruction will be defined later.

| Mnemonic  | Description   | Pseudocode    |
| :-------: | :------------ | :------------ |
|