# class I2C – a two-wire serial protocol

I2C is a two-wire protocol for communicating between devices. At the physical level it consists of 2 wires: SCL and SDA, the clock and data lines respectively. OpenMV Cam does not provide Pullups on the SDA or SCL lines and external pullups are required on both SDA and SCL lines for the I2C bus to be functional.

I2C objects are created attached to a specific bus. They can be initialised when created, or initialised later on.

Example:

    from pyb import I2C

    i2c = I2C(2)                         # create on bus 2
    i2c = I2C(2, I2C.MASTER)             # create and init as a master
    i2c.init(I2C.MASTER, baudrate=20000) # init as a master
    i2c.init(I2C.SLAVE, addr=0x42)       # init as a slave with given address
    i2c.deinit()                         # turn off the peripheral

Printing the i2c object gives you information about its configuration.

The basic methods are send and recv:

    i2c.send('abc')      # send 3 bytes
    i2c.send(0x42)       # send a single byte, given by the number
    data = i2c.recv(3)   # receive 3 bytes

To receive inplace, first create a bytearray:

    data = bytearray(3)  # create a buffer
    i2c.recv(data)       # receive 3 bytes, writing them into data

You can specify a timeout (in ms):

    i2c.send(b'123', timeout=2000)   # timeout after 2 seconds

A controller must specify the recipient’s address:

    i2c.init(I2C.CONTROLLER)
    i2c.send('123', 0x42)        # send 3 bytes to peripheral with address 0x42
    i2c.send(b'456', addr=0x42)  # keyword for address

Master also has other methods:

    i2c.is_ready(0x42)           # check if peripheral 0x42 is ready
    i2c.scan()                   # scan for peripherals on the bus, returning
                                 #   a list of valid addresses
    i2c.mem_read(3, 0x42, 2)     # read 3 bytes from memory of peripheral 0x42,
                                 #   starting at address 2 in the peripheral
    i2c.mem_write('abc', 0x42, 2, timeout=1000) # write 'abc' (3 bytes) to memory of peripheral 0x42
                                                # starting at address 2 in the peripheral, timeout after 1 second

## Constructors

class pyb.I2C(bus, ...)

  Construct an I2C object on the given bus. `bus` can be 2 or 4. With no additional parameters, the I2C object is created but not initialised (it has the settings from the last initialisation of the bus, if any). If extra arguments are given, the bus is initialised. See `init` for parameters of initialisation.

  The physical pins of the I2C busses on the OpenMV Cam are:

  > - `I2C(2)` is on the Y position: `(SCL, SDA) = (P4, P5) = (PB10, PB11)`

  The physical pins of the I2C busses on the OpenMV Cam M7 are:

  > - `I2C(2)` is on the Y position: `(SCL, SDA) = (P4, P5) = (PB10, PB11)`

  > - `I2C(4)` is on the Y position: `(SCL, SDA) = (P7, P8) = (PD12, PD13)`

## Methods

I2C.deinit()

  Turn off the I2C bus.

I2C.init(mode, *, addr=0x12, baudrate=400000, gencall=False, dma=False)

  Initialise the I2C bus with the given parameters:

  > > - `mode` must be either `I2C.CONTROLLER` or `I2C.PERIPHERAL`

  > > - `addr` is the 7-bit address (only sensible for a peripheral)

  > > - `baudrate` is the SCL clock rate (only sensible for a controller)

  > > - `gencall` is whether to support general call mode

  > > - `dma` is whether to allow the use of DMA for the I2C transfers (note that DMA transfers have more precise timing but currently do not handle bus errors properly)

  > The actual clock frequency may be lower than the requested frequency. This is dependant on the platform hardware. The actual rate may be determined by printing the I2C object.

I2C.is_ready(addr)

  Check if an I2C device responds to the given address. Only valid when in controller mode.

I2C.mem_read(data, addr, memaddr, *, timeout=5000, addr_size=8)

  Read from the memory of an I2C device:

  > - `data` can be an integer (number of bytes to read) or a buffer to read into

  > - `addr` is the I2C device address

  > - `memaddr` is the memory location within the I2C device

  > - `timeout` is the timeout in milliseconds to wait for the read

  > - `addr_size` selects width of memaddr: 8 or 16 bits

  Returns the read data. This is only valid in controller mode.

I2C.mem_write(data, addr, memaddr, *, timeout=5000, addr_size=8)

  Write to the memory of an I2C device:

  > - `data` can be an integer or a buffer to write from

  > - `addr` is the I2C device address

  > - `memaddr` is the memory location within the I2C device

  > - `timeout` is the timeout in milliseconds to wait for the write

  > - `addr_size` selects width of memaddr: 8 or 16 bits

  Returns `None`. This is only valid in controller mode.

I2C.recv(recv, addr=0x00, *, timeout=5000)

  Receive data on the bus:

  > - `recv` can be an integer, which is the number of bytes to receive, or a mutable buffer, which will be filled with received bytes

  > - `addr` is the address to receive from (only required in controller mode)

  > - `timeout` is the timeout in milliseconds to wait for the receive

  Return value: if `recv` is an integer then a new buffer of the bytes received, otherwise the same buffer that was passed in to `recv`.

I2C.send(send, addr=0x00, *, timeout=5000)

  Send data on the bus:

  > - `send` is the data to send (an integer to send, or a buffer object)

  > - `addr` is the address to send to (only required in controller mode)

  > - `timeout` is the timeout in milliseconds to wait for the send

  Return value: `None`.

I2C.scan()

  Scan all I2C addresses from 0x01 to 0x7f and return a list of those that respond. Only valid when in controller mode.

## Constants

I2C.CONTROLLER

  for initialising the bus to controller mode

I2C.PERIPHERAL

  for initialising the bus to peripheral mode

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External links
  openmv.io
  forums.openmv.io
  github.com/openmv/openmv
  micropython.org
  forum.micropython.org
  github.com/micropython/micropython