In the world of electronics, memory plays a critical role in virtually every device, from small embedded systems to complex computers. However, not all microcontrollers and devices come with enough built-in memory to support more demanding applications. This is where external memory chips come into play. One such chip is the TMS4464-10NL, a 64K x 4-bit DRAM (Dynamic Random Access Memory) module, which can be used to expand the memory capacity of a microcontroller or embedded system.
In this DIY electronics project, we will demonstrate how to build a memory expansion module using the TMS4464-10NL. This project involves connecting the DRAM chip to a microcontroller and controlling it to read from and write to memory locations. The goal of this project is to create a simple, yet functional, memory expansion that can be used to increase the memory capabilities of small embedded systems, such as a basic microcontroller-driven device or a simple computing platform.
Materials Needed:
● TMS4464-10NL DRAM Chip
● Microcontroller (e.g., ATMEGA328 or similar)
● Breadboard and jumper wires
● Voltage regulators (e.g., LM7805) to provide 5V power
● Capacitors (100nF, 10uF) for power stabilization
● Resistors (various values)
● Transistors (e.g., 2N3906) to control chip enable and other signals
● Address Decoding Logic (using gates or a simple multiplexer)
● Push Buttons for manual triggering of memory operations
● LEDs for status indication
Step-by-Step Guide to Building the Project:
1. Understanding the TMS4464-10NL DRAM Chip
Before diving into the hardware, it's important to understand the TMS4464-10NL's function and pinout. The TMS4464 is a 64K x 4-bit DRAM, meaning it can hold 64K addresses, each with 4 bits of data. This chip is typically used for temporary data storage and requires constant refreshing to maintain the data integrity.
Key features of the TMS4464-10NL include:
● 64K x 4-bit organization: It has 64K addressable locations, each holding 4 bits of data.
● Refresh: Since it is dynamic RAM, the TMS4464 requires periodic refresh cycles to retain the stored data. This refresh is managed by the microcontroller or additional control circuitry.
● Control Pins: The chip has several control pins that manage read/write operations, chip enabling, and refresh cycles:
— CS (Chip Select): Enables the chip for reading or writing.
— RAS (Row Address Strobe) and CAS (Column Address Strobe): These are used to access different parts of the memory by selecting rows and columns.
— WE (Write Enable): Activates the write operation.
— OE (Output Enable): Allows the chip to output data onto the bus.
— D0-D3: Data lines for reading/writing 4 bits of data.
The TMS4464 requires a 5V power supply for operation and operates on a 16-bit address bus (i.e., 8 bits for the row address and 8 bits for the column address). It also needs periodic refresh cycles to maintain the data, which requires additional timing control that we'll handle with the microcontroller.
2. Setting Up the Microcontroller Interface
To interface the TMS4464 DRAM chip with a microcontroller, you need to manage the data bus, address bus, and control pins. This process requires understanding how the memory is addressed (using both row and column addresses) and how to perform read/write operations.
Addressing:
The TMS4464 uses a multiplexed address system. The row address (RAS) and column address (CAS) are sent in two parts to access a memory location. This means you'll need to set up a system for controlling both address lines and managing the strobe signals (RAS and CAS) properly. The microcontroller can generate the correct address lines and timing to interact with the DRAM.
● Address Bus: The microcontroller will output address values through its GPIO pins, which are connected to the DRAM’s address pins. Since the TMS4464 uses a 16-bit address space, the microcontroller will need to handle 16 bits of addressing, which could be mapped to multiple pins on the microcontroller’s port or multiplexed through external logic like multiplexers.
Control Signals:
Control signals are used to initiate the reading and writing processes.
● CS (Chip Select): The microcontroller needs to send a low signal to enable the chip for communication.
● RAS (Row Address Strobe) and CAS (Column Address Strobe): These signals need to be toggled in the correct sequence to specify the row and column of the memory cell that you want to read or write from.
● WE (Write Enable): This signal controls whether the microcontroller is performing a read or write operation. To write data, WE should be low. For a read, WE should be high.
● OE (Output Enable): This pin controls when data is output from the chip.
By controlling these signals, the microcontroller can interact with the DRAM to read and write data.
3. Powering the Circuit
The TMS4464-10NL DRAM chip operates at 5V, so you will need a stable 5V power supply to power the chip and the microcontroller. Use a voltage regulator such as the LM7805 to step down a higher voltage supply to the necessary 5V.
In addition, it’s good practice to add capacitors (100nF and 10uF) near the power pins of the microcontroller and DRAM to ensure power stability. These capacitors filter out noise and stabilize the voltage supply to prevent data corruption.
4. Setting Up the Address Decoding and Refresh Logic
Since the DRAM chip requires periodic refresh cycles, the microcontroller needs to be programmed to manage these refresh operations. The microcontroller will periodically send refresh commands to ensure that the data stored in the DRAM chip does not get lost.
To address the memory and refresh the data, you may use basic logic gates or a multiplexer. This setup will allow the microcontroller to select different rows and columns for data storage, while also triggering refresh cycles at regular intervals.
5. Building the Circuit
Now that you have an understanding of the TMS4464-10NL DRAM chip’s operation and how to control it, you can start building the circuit on a breadboard.
● Microcontroller: Connect the address lines from the microcontroller to the row and column address pins of the DRAM. Use multiplexers or additional logic gates if necessary.
● Control Signals: Connect the CS, RAS, CAS, WE, and OE pins of the DRAM to the microcontroller’s GPIO pins. You may need to use transistors to interface the microcontroller signals with the appropriate voltage levels.
● Power Supply: Provide a stable 5V supply to both the microcontroller and the DRAM. Add capacitors near the power pins for stability.
● Push Buttons: Connect buttons to trigger read/write operations. You could use one button to write data to memory and another to read the data.
● LED Indicators: Use LEDs to indicate when the DRAM is actively being written to or read from.
6. Testing and Debugging
Once the circuit is assembled, the next step is testing. Start by checking that the microcontroller can correctly write and read data to/from the DRAM.
● Use an oscilloscope or logic analyzer to monitor the timing of the address, data, and control signals. This will help you verify that the signals are being sent at the right times and that the DRAM is being addressed correctly.
● You may need to debug the system by observing the refresh cycles and ensuring that the data is not corrupted due to missing refresh operations.
7. Expanding the Project
Once you have the basic memory module working, you can consider expanding it. For example, you could:
● Add more DRAM chips to increase the available memory.
● Implement a simple memory controller to handle more complex memory operations.
● Create a more user-friendly interface, such as a keypad or LCD screen, to allow for easy data input and output.
8. Conclusion
This DIY electronics project demonstrates how to interface the TMS4464-10NL DRAM chip with a microcontroller to create a memory expansion module. Although DRAM requires more complex control than simpler memory types like EEPROM or flash memory, this project gives you valuable experience in memory management, addressing, and control signal timing. By building this memory expansion, you gain insight into how embedded systems can be expanded with external memory, enabling more sophisticated applications.