8-bit computer RAM intro

Introduction

This tutorial introduces you to the fundamentals of building a 16-byte by 8-bit static RAM for an 8-bit computer, as demonstrated by Ben Eater. Understanding the principles behind static RAM (SRAM) is essential for anyone interested in computer architecture and design. This guide will walk you through the key concepts and components involved in building your own RAM.

Step 1: Understand the Basics of Static RAM

Before diving into building SRAM, it’s vital to grasp how it works:

• Static RAM (SRAM) retains data bits as long as power is supplied.
• It uses bistable latching circuitry to store each bit, which is faster and more reliable than Dynamic RAM (DRAM).
• The structure we will be building consists of 16 bytes, with each byte containing 8 bits.

Step 2: Components Needed

Gather the following components to build your SRAM:

• 74LS189 Integrated Circuit (IC): This is a 4-bit static RAM chip that allows you to build the 8-bit structure by combining two of these chips.
• Power Supply: Ensure you have a stable power source, typically 5V.
• Breadboard and jumper wires: For assembling the circuit.
• Additional components: Resistors, capacitors, and switches for control signals.

Step 3: Circuit Design

Design the circuit layout for your SRAM:

• Use two 74LS189 chips to create 8 bits.
• Connect the data input and output pins according to the chip's datasheet.
• Ensure the address lines are connected to allow access to the 16 bytes.
• Add control signals for read and write operations.

Step 4: Assemble the SRAM

Follow these steps to assemble your SRAM on a breadboard:

1. Insert the ICs: Place the 74LS189 chips on the breadboard.
2. Connect Power and Ground: Attach the power supply to the Vcc and ground pins of the ICs.
3. Wiring Data Lines: Connect the data input/output lines of both chips.
4. Address Lines: Wire the address lines to allow selection of each byte.
5. Control Pins: Connect the read and write control pins to switches for user interaction.

Step 5: Testing the RAM

Once assembled, it’s time to test your static RAM:

• Use a simple program or a microcontroller to write data to the RAM.
• Verify that you can read back the data correctly.
• Check for stability by ensuring data remains intact after multiple read/write cycles.

Conclusion

You have now learned the foundational steps to build a 16-byte by 8-bit static RAM using a 74LS189 integrated circuit. This project not only enhances your understanding of computer memory but also provides hands-on experience in circuit assembly and testing. Next, consider exploring how to connect your RAM to a microprocessor or further delve into more complex memory designs. Happy building!