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cI2C Build Status

Arduino Hardware I2C for AVR (plain c)

Hardware I2C library for AVR MCUs (lib intended for I2C protocols development in c, for easier ports to other MCUs)

Library choice

  • cI2C library implements I2C bus for AVR targets (Uno, Nano, Mega...)
    • you may prefer this one when:
      • working on AVR targets
      • interrupts are not needed
  • WireWrapper implements I2C bus for every platform that includes Wire library
    • you would have to use this one when:
      • working on non-AVR targets
      • portability is needed (using Wire library)

No refactoring is required when switching between cI2C & WireWrapper libs; Both libs share same Typedefs, Functions & Parameters.


  • cI2C is written in plain c (intentionally)
  • cI2C does not use any interrupt (yet, but soon will have to)
  • cI2C is designed to act as bus Master (Slave mode will be considered in future releases)
  • cI2C is set to work on AVR targets only
    • for other targets, you may use WireWrapper instead (will be using Wire)


This library is intended to be able to work with multiple slaves connected on the same I2C bus. Thus, the I2C bus and Slaves are defined separately.

  • On one hand, I2C bus has to be initialized with appropriate speed:
    • use I2C_init(speed): speed can be chosen from I2C_SPEED enum for convenience, or passing an integer as parameter
  • On the other hand, Slave(s) have to be defined and initialized too:
    • use I2C_SLAVE typedef to declare slaves structs
    • use I2C_slave_init(pSlave, addr, regsize)
      • pSlave: pointer to the slave struct to initialize
      • addr: slave I2C address (don’t shift addr, lib takes care of that)
      • regsize: width of internal slave registers (to be chosen from I2C_INT_SIZE)
    • in case you need to use custom R/W procedures for a particular slave:
      • use I2C_slave_set_rw_func(pSlave, pFunc, rw)
        • pSlave: pointer to the slave declaration to initialize
        • pFunc: pointer to the Read or Write bypass function
        • rw: can be chosen from I2C_RW enum (wr=0, rd=1)

After all inits are done, the lib can basically be used this way:

  • I2C_read(pSlave, regaddr, pData, bytes)
    • pSlave: pointer to the slave struct to read from
    • regaddr: start address to read from
    • pData: pointer to the place where datas read will be stored
    • bytes: number of bytes to read from slave
    • returns true if read is ok, false otherwise
  • I2C_write(pSlave, regaddr, pData, bytes)
    • pSlave: pointer to the slave struct to write to
    • regaddr: start address to write to
    • pData: pointer to the block of datas to write to slave
    • bytes: number of bytes to write to slave
    • returns true if write is ok, false otherwise

Examples included

following examples should work with any I2C EEPROM/FRAM with address 0x50 (yet function to get Chip ID are device dependent (and will probably only work on FUJITSU devices))


Doxygen doc can be generated using “Doxyfile”.

See generated documentation

Release Notes

See release notes

See also