What is it?

ST Microelectronics' M24M02DRC 2 Mbit I2C EEPROM

The M24M02DRC EEPROMS are very low power devices and can handle voltages from 1.8 to 5.5 V. This means that the breakout board can be used with an Arduino UNO without logic level converters but more interestingly can be powered via digitalWrite(HIGH) to VIN and digitalWrite(LOW) to GND from any convenient GPIO pins. For the Teensy 3.1, this means that the board can be mounted on the top to access I2C pins 16/17 or on the bottom to access I2C pins 18/19 and the power and ground can be taken from pins 8 and 9, or 7 and 6, respectively.

The two EEPROM devices have different I2C addresses, and the data page access is via part of the device address. This means that the first EEPROM has I2C addresses 0x50, 0x51, 0x52 and 0x53 (0x50 | 0x00, 0x50 | 0x01, 0x50 | 0x02 and 0x50 | 0x03) while the second has I2C device addresses 0x54, 0x55, 0x56, and 0x57 (0x54 | 0x00, 0x54 | 0x01, 0x54 | 0x02 and 0x54 | 0x03). In addition, each EEPROM has an ID page accessed via I2C address 0x58 and 0x5C, respectively. This ID page can be locked to permanently store data that can be read only.

The breakout board has two solder jumpers that control the write protect of each EEPROM. If the trace between the solder jumpers is cut, the EEPROM can be read from but not written to. Resoldering the jumper returns the EEPROM to its writable state.

These EEPROMs are in a wafer level package, meaning they are essentially silicon wafers mounted on some solder balls attached to the pc board. They don't like rough handling nor bright light, as the latter can damage the silicon lattice and affect the memory cells of the chip.

The 2097152 bits of each EEPROM are organized as 1024 pages (pages 0 - 1023), and 256 bytes (0 - 255) per page. The data are accessed via an 18-bit address. The sketch I wrote for the breakout board uses four quadrants determined by the 2-bit XSadd, and then the MSadd and LSadd of the remaining 65536 bytes. Thus the 18-bit address of a byte will be XSadd << 16 | MSadd << 8 | LSadd. The XSadd will be appended to the device I2C address in the read and write functions.

The sketch demonstrates single byte, multiple byte, and 256-byte page reads and writes. These EEPROMS are really easy to use!

Why did you make it?

Permanent storage in a small package is useful for all kinds of projects. They are especially useful for data logging. A typical IMU plus pressure sensor might produce 24 bytes per time stamp. At once per second, this EEPROM package can hold almost six hours of continuous data. For remote weather station or earthquake detection applications, the data can be logged for days. There is no limit to the uses you can find for this memory solution. The EEPROMS require so little power, they can run off of a battery for weeks. And even if the battery runs out of power, they retain their data for later download.

What makes it special?

These EEPROMS offer 256 kbytes each in an appallingly small package that fits almost anywhere. The EEPROMS can be written and read over four million times. Each page write or read takes at most 10 milliseconds. The data can be write-protected and the non-volatile memory retains the data uncorrupted for 200 years!

Order the board from OSH Park and assemble your own or order an assembled and fully tested board from me and see how useful 512 kbytes in a small package can be!