I2C_EEPROM

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

Description

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

Interface

Constructor

• 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 and checks if the device is available on the I2C bus.
• bool begin(uint8_t sda, uint8_t scl) idem for ESP32 / ESP8266 and alike.
• bool isConnected() test to see if deviceAddress is found on the bus.

Core functions

• int writeByte(uint16_t memoryAddress, uint8_t value) write a single byte to the specified memory address.
• 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.
• int writeBlock(uint16_t memoryAddress, uint8_t * buffer, uint16_t length) write a buffer starting at the specified memory address.
• int updateBlock(uint16_t memoryAddress, uint8_t * buffer, uint16_t length) write a buffer starting at the specified memory address, but only if changed.
• 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 0 if OK.
• 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.

Other

• 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 gives 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.

UpdateBlock()

(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_BUFFERSIZE (== 30 on AVR limitation). 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()

ExtraWriteCycleTime (experimental)

(new since 1.5.1)

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

Limitation

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

Future

• improve error handling, write functions should return bytes written or so.
• what can we do with the print interface? (investigate)
• investigate multi-EEPROM storage,
• investigate smarter strategy for updateBlock() => find first and last changed position could possibly result in less writes.
• can setBlock use strategies from update

Operational

See examples