8-Bit Computer from Scratch (Built with Logic Gates)

Welcome to the documentation repository for my custom-built 8-bit computer, constructed entirely from logic gates and basic components. This project is a deep dive into computer architecture, taking inspiration from classic microprocessors and educational systems, but designed from the ground up with a custom Instruction Set Architecture (ISA), control logic, and microcode.

🔧 Project Overview

This project is about understanding and constructing the fundamental building blocks of a computer:

• Registers and ALU
• Program Counter and Memory
• Instruction Decoder and Control Unit
• Microcoded Control Logic
• Arithmetic, Logic, and Comparison Units
• Bus-based Data Architecture
• Seven-Segment Display Output

🧠 Key Components

• Registers A-D: General-purpose 8-bit registers.
• ALU: Supports operations like ADD, SUB, AND, OR, XOR, NOT, CMP.
• Program Counter: Controls instruction flow with PCI, PCC, and PCE control signals.
• RAM: General memory with input/output controls (MeI, MeO).
• Microcode ROM / Control Unit: Controls signal sequencing for instruction execution.
• Instruction Register: Stores the current instruction fetched from memory.
• Temp Registers: Temporary internal storage for multi-step operations.
• Flag Register: Holds status flags (Zero, Carry).
• 7-Segment Display: Used for displaying output values in decimal format.

📁 Repository Structure

.
├── Compiler/                        # Basic assembler for the custom ISA
├── Datasheets/                      # Datasheets for different ICs
├── Docs/
|   ├── HwDesign.md                  # Details about hardware design
|   ├── ISA.md                       # Details and documentation of supported instructions
│   └── SignalInfo.md                # Information about all the control signals
├── EepromFlasher/
|   ├── App/                         # GUI Application for flash binary in eeprom
│   └── Firmware/                    # Firmware code for the arduino for the eeprom flasher
├── Gen7segDriver/                   # 7 Segment display driver EEPROM logic
├── Images/
│   ├── Schematic/                   # Schematic diagram for each PCB
│   └── BlockDiagram/                # Top level block diagrams
|       └── TopLevelArchitecture.png # High-level block diagram of the computer
├── MicroCode/
│   └── GenMicrocode.py              # Microcode definitions and sequencing logic
└── README.md

🛠 Features

• Complete microcoded control unit for all supported instructions.
• Instruction decoder and sequencer implemented with logic.
• Custom ISA with binary opcode support.
• Support for logic-level debugging and test forcing.
• Graphical output via 7-segment display.

🧾 Instruction Set

Documentation about the supported instructions (ADD, SUB, AND, OR, MOV, JMP, etc.) is available in the ISA.md file.

Each instruction is defined with:

• Opcode
• Control signal sequences
• Clock cycles
• Examples

🛠 Control Signals

Documentation about all the control signal is available in the SignalInfo.md file.

In the HwDesign.md file, placement of the signals ins the bus is shown visually.

📸 Visuals

• Block Diagram: Images/BlockDiagram/TopLevelArchitecture.png
• Future updates may include breadboard photos, logic analyzer screenshots, and waveforms.

🎯 Goals

• Learn computer architecture hands-on.
• Build a fully functional 8-bit computer using only logic gates.
• Design and implement a custom ISA.
• Optionally simulate with Logisim/Verilog for verification.

📬 Feedback & Contributions

This is a personal learning project, but contributions, discussions, and feedback are welcome! Feel free to open an issue or pull request if you'd like to contribute.

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Built with ❤️ from logic gates.