Arduino Library for external I2C EEPROM - 24LC512, 24LC256, 24LC64/32/16/08/04/02/01.

This library is to access external I2C EEPROM up to 64KB (= 512 Kbit) in size. MicroChip 24LC512, 24LC256, 24LC64, 24LC32, 24LC16, 24LC08, 24LC04, 24LC02, 24LC01 and equivalents.

The I2C_eeprom_cyclic_store interface is documented here

        +---U---+
    A0  | 1   8 |  VCC = +5V
    A1  | 2   7 |   WP = write protect pin
    A2  | 3   6 |  SCL = I2C clock
   GND  | 4   5 |  SDA = I2C data
        +-------+

default address = 0x50 .. 0x57 depending on three address lines

The interface is kept quite identical to the I2C_24LC1025 library. https://github.com/RobTillaart/I2C_24LC1025

Most important change is 32 bit memory addresses.

• I2C_eeprom(uint8_t deviceAddress, TwoWire *wire = &Wire) constructor, optional Wire interface.
• I2C_eeprom(uint8_t deviceAddress, uint32_t deviceSize, TwoWire *wire = &Wire) constructor, with optional Wire interface.
• bool begin() initializes the I2C bus with the default pins. Furthermore it checks if the deviceAddress is available on the I2C bus. Returns true if deviceAddress is found on the bus, false otherwise.
• bool begin(uint8_t sda, uint8_t scl) (ESP32 / ESP8266 only) initializes the I2C bus with the specified pins, therby overruling the default pins. Furthermore it checks if the deviceAddress is available on the I2C bus. Returns true if deviceAddress is found on the bus, false otherwise.
• bool isConnected() test to see if deviceAddress is found on the bus.

• int writeByte(uint16_t memoryAddress, uint8_t value) write a single byte to the specified memory address. Returns I2C status, 0 = OK.
• int writeBlock(uint16_t memoryAddress, uint8_t * buffer, uint16_t length) write a buffer starting at the specified memory address. Returns I2C status, 0 = OK.
• int setBlock(uint16_t memoryAddress, uint8_t value, uint16_t length) writes the same byte to length places starting at the specified memory address. Returns I2C status, 0 = OK.

• int updateByte(uint16_t memoryAddress, uint8_t value) write a single byte, but only if changed. Returns 0 if value was same or write succeeded.
• uint16_t updateBlock(uint16_t memoryAddress, uint8_t * buffer, uint16_t length) write a buffer starting at the specified memory address, but only if changed. Returns bytes written.

• uint8_t readByte(uint16_t memoryAddress) read a single byte from a given address.
• uint16_t readBlock(uint16_t memoryAddress, uint8_t * buffer, uint16_t length) read length bytes into buffer starting at specified memory address. Returns the number of bytes read, which should be length.

Since 1.6.0. - experimental, needs extensive testing.

Same as write and update functions above. Returns true if successful, false indicates an error.

• bool writeByteVerify(uint16_t memoryAddress, uint8_t value)
• bool writeBlockVerify(uint16_t memoryAddress, uint8_t * buffer, uint16_t length)
• bool setBlockVerify(uint16_t memoryAddress, uint8_t value, uint16_t length)
• bool updateByteVerify(uint16_t memoryAddress, uint8_t value)
• bool updateBlockVerify(uint16_t memoryAddress, uint8_t * buffer, uint16_t length)

• uint32_t getDeviceSize() idem
• uint8_t getPageSize() idem
• uint8_t getPageSize(uint32_t deviceSize) idem
• uint32_t getLastWrite() idem
• uint32_t determineSize(bool debug = false) function that determines the size of the EEPROM by detecting when a memory address is folded upon memory address 0. It is based upon the observation that memory wraps around. The debug flag prints some output to Serial.

Warning: this function has changed (again) in 1.4.0

Test results

The function cannot detect smaller than 128 bit EEPROMS.

(new since 1.4.2)

The function updateBlock() reads the block of data and compares it with the new values to see if it needs rewriting.

As the function reads/writes the data in blocks with a maximum length of I2C_TWIBUFFERSIZE (== 30 AVR limitation; 128 for ESP32) It does this comparison in chunks if the length exceeds this number. The result is that an updateBlock() call can result e.g. in 4 reads and only 2 writes under the hood.

If data is changed often between writes, updateBlock() is slower than writeBlock(). So you should verify if your sketch can make use of the advantages of updateBlock()

To improve support older I2C EEPROMs e.g. IS24C16 two functions were added to increase the waiting time before a read and/or write as some older devices have a larger timeout than 5 milliseconds which is the minimum.

• void setExtraWriteCycleTime(uint8_t ms) idem
• uint8_t getExtraWriteCycleTime() idem

The library does not offer multiple EEPROMS as one continuous storage device.

See examples

• improve documentation

• investigate multi-EEPROM storage
  • wrapper class?
• improve error handling, write functions should return bytes written or so.

• investigate smarter strategy for updateBlock() => find first and last changed position could possibly result in less writes.
• can setBlock() use strategies from updateBlock()
• _waitEEReady(); can return bool and could use isConnected() internally.
  • added value?
• investigate the print interface?
  • circular buffer? (see FRAM library)
  • dump function?