Build an 8-bit decimal display for our 8-bit computer

Introduction

In this tutorial, you will learn how to build an 8-bit decimal display for an 8-bit computer using an EEPROM (28C16). The project utilizes multiplexing to control four digits with a single EEPROM, allowing you to display both unsigned and signed (twos complement) values. This guide will walk you through the necessary components, wiring, and programming to successfully complete your display.

Step 1: Gather Required Components

Before you start building, ensure you have the following components:

• 1x 28C16 EEPROM
• 1x 555 timer IC
• 1x 74LS76 (Dual JK flip-flop)
• 1x 74LS139 (Dual 2-line to 4-line decoder)
• 4x Common cathode 7-segment displays
• 1x 1k resistor
• 1x 100k resistor
• 2x 10nF capacitors

Practical Advice

• Check the specifications of your components to ensure compatibility.
• Organize your workspace to keep track of all parts.

Step 2: Setup the Circuit

1. Connect the EEPROM

   • Insert the 28C16 EEPROM into the breadboard.
   • Ensure the connections to power (Vcc) and ground (GND) are secure.

2. Wire the 555 Timer IC

   • Connect the 555 timer in astable mode to generate a clock signal.
   • Use the following connections:
     • Pin 1 to Ground
     • Pin 8 to Vcc
     • Connect resistors and capacitors to the appropriate pins to set the frequency.

3. Attach the JK Flip-Flop

   • Insert the 74LS76 flip-flop into the breadboard.
   • Connect its clock input to the output of the 555 timer to synchronize the counting.

4. Connect the 2-line to 4-line Decoder

   • Place the 74LS139 decoder on the breadboard.
   • Wire it to accept inputs from the flip-flop and drive the 7-segment displays.

5. Wire the 7-segment Displays

   • Connect the common cathode of each 7-segment display to ground.
   • Connect the segments (A to G) to the outputs of the 74LS139.

Practical Advice

• Double-check connections against the circuit diagram to avoid errors.
• Use jumper wires to make connections neat and easy to follow.

Step 3: Program the EEPROM

1. Download the Code

   • Access the code for programming the EEPROM from GitHub.

2. Modify the Code (if necessary)

   • Adjust any parameters based on your circuit configuration.

3. Upload the Code to the EEPROM

   • Use an EEPROM programmer to upload the code to your 28C16.
   • Ensure the correct settings are selected for the programming process.

Practical Advice

• Familiarize yourself with the EEPROM programmer’s interface for a smooth programming experience.
• Test the code in a simulation environment if available, before uploading.

Step 4: Test the Display

1. Power On the Circuit

   • Once everything is connected and programmed, power on your circuit.

2. Check the Output

   • Verify that the 7-segment displays are showing the correct decimal values.
   • Test both unsigned and signed modes to ensure functionality.

Common Pitfalls to Avoid

• Ensure the EEPROM is correctly seated in the breadboard.
• Double-check all connections if the display does not work as expected.

Conclusion

You have successfully built an 8-bit decimal display using an EEPROM and various components. This project not only demonstrates the use of multiplexing but also enhances your understanding of digital displays. For further learning, consider exploring more advanced projects or integrating this display into a larger system. Happy building!