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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.

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(1)                             # create on bus 1
i2c = I2C(1, I2C.CONTROLLER)             # create and init as a controller
i2c.init(I2C.CONTROLLER, baudrate=20000) # init as a controller
i2c.init(I2C.PERIPHERAL, addr=0x42)      # init as a peripheral with given address
i2c.deinit()                             # turn off the I2C unit

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 1 or 2, ‘X’ or ‘Y’. 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 buses on Pyboards V1.0 and V1.1 are:

  • I2C(1) is on the X position: (SCL, SDA) = (X9, X10) = (PB6, PB7)

  • I2C(2) is on the Y position: (SCL, SDA) = (Y9, Y10) = (PB10, PB11)

On the Pyboard Lite:

  • I2C(1) is on the X position: (SCL, SDA) = (X9, X10) = (PB6, PB7)

  • I2C(3) is on the Y position: (SCL, SDA) = (Y9, Y10) = (PA8, PB8)

Calling the constructor with ‘X’ or ‘Y’ enables portability between Pyboard types.

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