How to Use Adafruit SPI FRAM: Examples, Pinouts, and Specs

The Adafruit SPI FRAM is a non-volatile memory module that utilizes ferroelectric random access memory (FRAM) technology. This component is designed for applications requiring high-speed data writing, low power consumption, and the ability to retain data without power. It is ideal for use in data logging, real-time clocks, and other scenarios where data must be preserved across power cycles.

• Data logging systems
• Real-time clocks
• Industrial control systems
• Gaming and entertainment devices
• Wearable electronics

• Voltage Supply: 3.3V to 5V
• Operating Current: 10 mA (typical)
• Memory Size: Varies by model (e.g., 32Kbit, 64Kbit)
• Interface: SPI (Serial Peripheral Interface)
• Data Retention: 10+ years
• Write Endurance: 10^14 write cycles

1. Power Supply: Connect VCC to a 3.3V or 5V power supply and VSS to ground.
2. SPI Interface: Connect MOSI, MISO, and SCK to the corresponding SPI pins on your microcontroller.
3. Chip Select: Connect the CS pin to a digital pin on your microcontroller for SPI communication.
4. Write Protect and Hold: Connect WP and HOLD to VCC if not used, or to a digital pin if control over these functions is required.

• Ensure that the power supply is within the specified voltage range.
• Use pull-up resistors on the CS, WP, and HOLD pins if they are not actively driven by the microcontroller.
• Avoid exposing the chip to temperatures outside the specified operating range.
• When integrating with a microcontroller, ensure that the SPI clock speed does not exceed the maximum frequency specified for the FRAM chip.

#include <SPI.h>
#include <Adafruit_FRAM_SPI.h>

// Pin definitions
#define CS_PIN 10

// Create an FRAM_SPI instance
Adafruit_FRAM_SPI fram = Adafruit_FRAM_SPI(CS_PIN);

void setup() {
  Serial.begin(9600);
  // Initialize SPI
  SPI.begin();
  
  // Initialize the FRAM module
  if (fram.begin()) {
    Serial.println("Found SPI FRAM");
  } else {
    Serial.println("No SPI FRAM found ... check your connections");
  }
  
  // Write data to FRAM
  uint8_t dataToWrite = 42; // Example data
  fram.writeEnable(true);
  fram.write8(0, dataToWrite);
  fram.writeEnable(false);
  
  // Read data from FRAM
  uint8_t readData = fram.read8(0);
  Serial.print("Data read from FRAM: ");
  Serial.println(readData);
}

void loop() {
  // Code to interact with FRAM can be placed here
}

• FRAM not detected: Ensure all connections are secure and the correct CS pin is defined in your code.
• Incorrect data read/write: Verify that the SPI clock speed is within the FRAM's operating range and that the power supply is stable.
• Write operations not persisting: Make sure the write protect (WP) pin is not active or incorrectly wired.

• Double-check wiring against the pin configuration table.
• Use serial output to debug and verify that initialization is successful.
• Ensure that the library used is up-to-date and compatible with your FRAM model.

Q: How long will the FRAM retain data? A: The FRAM is rated to retain data for over 10 years without power.

Q: Can I use the Adafruit SPI FRAM with a 5V microcontroller? A: Yes, the Adafruit SPI FRAM can operate with a supply voltage of up to 5V.

Q: How many write cycles can the FRAM handle? A: The FRAM can handle up to 10^14 write cycles, making it highly durable for write-intensive applications.

Q: Is it necessary to use the HOLD pin? A: The HOLD pin is optional and is used to pause communication without resetting the SPI connection. If not used, it should be tied to VCC.