.. currentmodule:: pyb
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.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 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
.. method:: I2C.deinit() Turn off the I2C bus.
.. method:: I2C.init(mode, *, addr=0x12, baudrate=400000, gencall=False, dma=False)
Initialise the I2C bus with the given parameters:
- ``mode`` must be either ``I2C.MASTER`` or ``I2C.SLAVE``
- ``addr`` is the 7-bit address (only sensible for a slave)
- ``baudrate`` is the SCL clock rate (only sensible for a master)
- ``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)
.. method:: I2C.is_ready(addr) Check if an I2C device responds to the given address. Only valid when in master mode.
.. method:: 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.
.. method:: 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.
.. method:: 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``.
.. method:: 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``.
.. method:: I2C.scan() Scan all I2C addresses from 0x01 to 0x7f and return a list of those that respond. Only valid when in master mode.
.. data:: I2C.MASTER for initialising the bus to master mode
.. data:: I2C.SLAVE for initialising the bus to slave mode