NPR 21-bit Computer Design

The NPR 21-bit Computer is a specialized architecture featuring a 21-bit word size, segmented into a 4-bit opcode for operation specification, a 15-bit address for memory referencing, and a 2-bit field for versatile addressing modes. This design accommodates four distinct addressing modes, enabling operations like immediate, direct, indirect, and indexed addressing.

Table of Contents

1. Key Features
2. Instruction Set Architecture
   • Memory Reference Instructions (MRIs)
   • Register Reference Instructions (RRIs)
   • Input-Output Instructions (IOIs)
3. Instruction Cycle
4. Design of Individual Components
5. How to Use the NPR 21-bit Computer Design Repository
   • Prerequisites
   • Steps to Run the Design
6. Demo
7. Contributing
8. Support
9. Conclusion

Key Features

• 21-bit word size
• 4-bit opcode
• 15-bit address
• 2-bit addressing mode field
• 32,768 memory locations
• Essential registers: Program Counter, Instruction Register, Accumulator, Memory Address Register, Memory Buffer Register
• Instruction set including load, store, add, subtract, and more

Instruction Set Architecture

The instruction set architecture of the NPR 21-bit Computer includes:

• Memory Reference Instructions (MRIs): 15 instructions with immediate, direct, and indirect addressing modes
• Register Reference Instructions (RRIs): 13 instructions for direct calculations and manipulations of data in registers
• Input-Output Instructions (IOIs): 8 instructions for communication between the computer and external devices

Instruction Cycle

The instruction cycle of the NPR 21-bit Computer consists of four main phases:

1. Fetch: The instruction is fetched from memory.
2. Decode: The opcode and addressing mode are decoded.
3. Execute: The specified operation is performed.
4. Interrupt: Handles interrupts if enabled.

Design of Individual Components

The NPR 21-bit Computer incorporates various components, including:

• Registers: AR, PC, TR, SC, IR, AC, DR, OUTR
• Flags: IEN, FGO, FGI, R, E, S, I0, I1
• Memory: 32K memory locations
• ALU: Performs arithmetic and logical operations
• Common Bus Control: Manages data transfer between components

How to Use the NPR 21-bit Computer Design Repository

To run the NPR 21-bit Computer design using Logisim, follow these steps:

Prerequisites

• Logisim: Ensure you have Logisim installed on your computer. You can download it from the official website or use a compatible version.
• NPR 21-bit Computer Design Files: Obtain the Logisim project files for the NPR 21-bit Computer design, which may be included in this repository or provided separately.

Steps to Run the Design

1. Open Logisim

   Launch the Logisim application on your computer.

2. Load the Project

   • Click on File in the menu bar.
   • Select Open and navigate to the directory where the NPR 21-bit Computer design files are located.
   • Open the main project file (with a .circ extension).

3. Familiarize Yourself with the Design

   Review the components of the NPR 21-bit Computer design within Logisim. Key components to look for include:

   • Registers: Such as the Program Counter (PC), Instruction Register (IR), and Accumulator (AC).
   • ALU: The Arithmetic Logic Unit for performing calculations.
   • Memory: The memory blocks where instructions and data are stored.
   • Control Unit: Manages the execution of instructions.

4. Simulate the Circuit

   • Click on the Simulate menu and select Tick to start the simulation.
   • You can also use the Run button to execute the program continuously.
   • Observe the behavior of the registers and ALU as instructions are executed.

5. Input Instructions

   • To test the functionality, you may need to input instructions into the memory. This can typically be done by clicking on the memory component and entering values directly.
   • Ensure that the instruction format adheres to the NPR 21-bit architecture, which consists of a 21-bit word with specific opcode and addressing mode bits.

6. Debugging and Monitoring

   • Utilize the Probe tool in Logisim to monitor the signals and outputs from various components.
   • Check the values in registers and memory to ensure that the instructions are being executed correctly.

7. Stopping the Simulation

   • To stop the simulation, click on the Simulate menu and select Stop.
   • You can then make any necessary changes to the circuit or the instructions before running the simulation again.

Demo

For a visual demonstration of the NPR 21-bit Computer in action, watch the following video on YouTube: NPR 21-bit Computer Design Simulation

Contributing

If you wish to contribute to the NPR 21-bit Computer project, please fork the repository and submit a pull request with your changes. Ensure that your contributions adhere to the project's coding standards and include appropriate documentation.

Support

For any questions or further information, feel free to reach out:

• Name: Prashant Manandhar
• Email: [email protected]
• GitHub: Eemayas
• Website: https://www.manandharprashant.com.np/

Conclusion

The NPR 21-bit Computer design showcases a comprehensive and advanced architectural framework, incorporating essential components and a diverse instruction set to enable efficient computation within its 32,768 memory locations. This project serves as a valuable resource for understanding the fundamental principles and design considerations of basic computer architectures.

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