RAM module build - part 3

Introduction

In this tutorial, we will build on our previous work by adding DIP switches and the necessary logic to input data into our RAM module manually. This is a continuation of creating an 8-bit computer's RAM module, focusing on enabling program mode for data entry and ensuring data can be written from the bus in run mode. By the end of this guide, you'll have a fully functional RAM module that allows for manual data input.

Step 1: Gather Required Components

Before starting the build process, ensure you have all the necessary components. Here’s the complete parts list:

• 2x 74LS189 (64-bit random access memory)
• 2x 74LS04 (Hex inverter)
• 1x 74LS173 (4-bit D-type register)
• 4x 74LS157 (Quad 2-to-1 line data selector)
• 1x 74LS245 (Octal bus transceiver)
• 1x 74LS00 (Quad NAND gate)
• 14x LEDs (9 red, 4 yellow, 1 green)
• 3x 1KΩ resistors
• 1x 0.01µF capacitor
• 22 gauge wire
• 5 volt power source (e.g., a USB phone charger)

Practical Tip

Purchase components from reliable electronic distributors like Jameco, Digikey, or Mouser.

Step 2: Set Up the DIP Switches

DIP switches will allow you to manually input data. Here’s how to set them up:

1. Choose Switches: Select a set of DIP switches appropriate for your RAM module.
2. Wiring: Connect the switches to the RAM module’s data input lines.
3. Pull-up Resistors: Use pull-up resistors to ensure that the switches default to a high state when not pressed.

Common Pitfalls

Ensure that the switches are wired correctly. Miswiring can lead to erroneous data input.

Step 3: Connect the Logic for Manual Input

Now, we need to integrate the logic that processes the input from the DIP switches. Follow these steps:

1. Connect to 74LS173: Wire the output from the DIP switches to the 74LS173 D-type register.
2. Control Signals: Set the control signals to allow data to be loaded into the register when the switches are toggled.
3. Output to RAM: Connect the output of the D-type register to the RAM module, ensuring it can receive the input data.

Practical Tip

Double-check signal paths to ensure the data can flow correctly from the switches to the RAM.

Step 4: Implement the Bus Writing Logic

Next, we will set up the logic to allow data to be written from the bus into RAM during run mode.

1. Connect 74LS245: Wire the octal bus transceiver to facilitate data transfer from the bus.
2. Control Logic: Use the 74LS00 NAND gate to create control logic that determines whether the RAM is in program mode or run mode.
3. Testing: After connecting, test to ensure that data can be written from the bus into RAM when in run mode.

Real-World Application

Understanding how to manage data flow between components is crucial for building effective computer systems.

Conclusion

In this tutorial, we successfully added DIP switches and the necessary logic for manually inputting data into our RAM module. By following these steps, you should now have a functional RAM module capable of manual data entry in program mode and data writing from the bus in run mode. As a next step, consider integrating this RAM module with other components of your 8-bit computer project. Happy building!