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.

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)   # timout after 2 seconds

A master must specify the recipient’s address:

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

Master also has other methods:

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

Constructors

Methods

i2c.deinit()

Turn off the I2C bus.

i2c.is_ready(addr)

Check if an I2C device responds to the given address. Only valid when in master 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 master 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 master 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 master 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.scan()

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

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 master mode)
  • timeout is the timeout in milliseconds to wait for the send

Return value: None.

Constants

I2C.MASTER

for initialising the bus to master mode