Technical summary
Description
This small board integrates a non-volatile MB85RC256V FRAM chip of 256 Mbits / 32 MB with I2C interface.
FRAM (ferroelectric random access memory) can be used like EEPROM or Flash memory for non-volatile storage, but it is better in almost every respect.
Unlike EEPROM or Flash memory, FRAM offers virtually unlimited read/write endurance, of at least 1000 billion cycles. Data retention is also very long and depends on temperature. FRAM is thus ideal for logging applications that require frequent, or even continuous, updating of the data on the chip. If one byte of data is updated every millisecond, it would take nearly 32 years to reach 1000 billion write cycles.
It is also possible to write at full bus speed, up to 1 MHz over I2C, without needing to poll the system as with an EEPROM in order to check that pages have been written or erased before rewriting them. You just overwrite the existing data, as with an SRAM.
The package includes:
- MB85RC256V 256 Mbits FRAM module
- 1x8 male connector
Main features of the 32K I2C FRAM module:
- 32 MB (256 Mbits) memory organized as 32 KB x 8 bytes
- I2C interface with built-in 10 kΩ pull-up resistors
- Clock frequency up to 1 MHz
- Minimum of 1 trillion read/write cycles per byte
- Long-term data retention: 200 years at 35 °C, 95 years at 55 °C, 10 years at 85 °C.
- Low power
- 3.3V and 5V compatibility
Module connections
The connections to the module are relatively simple.
- Provide a 3.3V or 5V supply matching the microcontroller, and ground.
- Connect the I2C interface.
- The optional write-protect and address lines can be used if needed.
1 x 8 header
- VCC : 2.7 to 5.5V. Typically connected to 3.3V or 5V to match the microcontroller supply.
- GND : Ground is connected to the microcontroller ground.
- WP: Write protection. Internally pulled low to allow writing. Connect it to Vcc if you want to disable writing to the chip.
- SCL : Clock – connects to I2C SCL.
- SDA : Data – connects to I2C SDA.
- A2 : Address bit 2. Internally held at ground.
- A1 : Address bit 1. Internally held at ground.
- A0 : Address bit 0. Internally held at ground.
I2C bus
The module works over I2C at a maximum bus frequency of 1 MHz. The maximum speed depends mainly on the microcontroller used. For example, an Uno or other slower 16-bit microcontrollers will generally be limited to 400 kHz, while faster 32-bit microcontrollers such as the Teensy or the ESP32 can reach 1 MHz.
The module includes 10 kΩ pull-up resistors on the I2C lines. In our tests with 10cm jumper wires, we were able to reach the maximum speed of 1 MHz without any problem. At higher speeds and with long cables, data errors can occur. In that case, you can add stronger pull-up resistors, for example 2.2 kΩ. These can be added in parallel with the ones already present on the module.
Addressing
The base address of the module is 0x50.
There are 3 address lines marked A0-A2 which can be used to change the base address if needed and allow up to 8 of these modules to be used on the same I2C bus by setting each one to a different address.
These pins are held low internally. To change the address, connect the address pins to Vcc. This gives an address range of 0x50 to 0x57. If pin A0 is connected to Vcc, the module address is 0x51, and so on.
