micropython/docs/library/machine.I2C.rst

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.. currentmodule:: machine
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.
.. only:: port_wipy
Example::
from machine import I2C
i2c = I2C(0) # create on bus 0
i2c = I2C(0, I2C.MASTER) # create and init as a master
i2c.init(I2C.MASTER, baudrate=20000) # init as a master
i2c.deinit() # turn off the peripheral
Printing the i2c object gives you information about its configuration.
.. only:: port_wipy
A master must specify the recipient's address::
i2c.init(I2C.MASTER)
i2c.writeto(0x42, '123') # send 3 bytes to slave with address 0x42
i2c.writeto(addr=0x42, b'456') # keyword for address
Master also has other methods::
i2c.scan() # scan for slaves on the bus, returning
# a list of valid addresses
i2c.readfrom_mem(0x42, 2, 3) # read 3 bytes from memory of slave 0x42,
# starting at address 2 in the slave
i2c.writeto_mem(0x42, 2, 'abc') # write 'abc' (3 bytes) to memory of slave 0x42
# starting at address 2 in the slave, timeout after 1 second
Constructors
------------
.. only:: port_wipy
.. class:: I2C(bus, ...)
Construct an I2C object on the given bus. `bus` can only be 0.
If the bus is not given, the default one will be selected (0).
.. only:: not port_wipy
.. class:: I2C(id=-1, \*, scl, sda, freq=400000)
Construct and return a new I2C object using the following parameters:
- `id` identifies the particular I2C peripheral. The default
value of -1 selects a software implementation of I2C which can
work (in most cases) with arbitrary pins for SCL and SDA.
If `id` is -1 then `scl` and `sda` must be specified. Other
allowed values for `id` depend on the particular port/board,
and specifying `scl` and `sda` may or may not be required or
allowed in this case.
- `scl` should be a pin object specifying the pin to use for SCL.
- `sda` should be a pin object specifying the pin to use for SDA.
- `freq` should be an integer which sets the maximum frequency
for SCL.
General Methods
---------------
.. only:: port_wipy
.. method:: I2C.init(mode, \*, baudrate=100000, pins=(SDA, SCL))
Initialise the I2C bus with the given parameters:
- ``mode`` must be ``I2C.MASTER``
- ``baudrate`` is the SCL clock rate
- ``pins`` is an optional tuple with the pins to assign to the I2C bus.
.. only:: port_esp8266
.. method:: I2C.init(scl, sda, \*, freq=400000)
Initialise the I2C bus with the given arguments:
- `scl` is a pin object for the SCL line
- `sda` is a pin object for the SDA line
- `freq` is the SCL clock rate
.. method:: I2C.deinit()
Turn off the I2C bus.
Availability: WiPy.
.. method:: I2C.scan()
Scan all I2C addresses between 0x08 and 0x77 inclusive and return a list of
those that respond. A device responds if it pulls the SDA line low after
its address (including a read bit) is sent on the bus.
Note: on WiPy the I2C object must be in master mode for this method to be valid.
Primitive I2C operations
------------------------
The following methods implement the primitive I2C master bus operations and can
be combined to make any I2C transaction. They are provided if you need more
control over the bus, otherwise the standard methods (see below) can be used.
.. method:: I2C.start()
Generate a START condition on the bus (SDA transitions to low while SCL is high).
Availability: ESP8266.
.. method:: I2C.stop()
Generate a STOP condition on the bus (SDA transitions to high while SCL is high).
Availability: ESP8266.
.. method:: I2C.readinto(buf, nack=True)
Reads bytes from the bus and stores them into `buf`. The number of bytes
read is the length of `buf`. An ACK will be sent on the bus after
receiving all but the last byte. After the last byte is received, if `nack`
is true then a NACK will be sent, otherwise an ACK will be sent (and in this
case the slave assumes more bytes are going to be read in a later call).
Availability: ESP8266.
.. method:: I2C.write(buf)
Write the bytes from `buf` to the bus. Checks that an ACK is received
after each byte and stops transmitting the remaining bytes if a NACK is
received. The function returns the number of ACKs that were received.
Availability: ESP8266.
Standard bus operations
-----------------------
The following methods implement the standard I2C master read and write
operations that target a given slave device.
.. method:: I2C.readfrom(addr, nbytes, stop=True)
Read `nbytes` from the slave specified by `addr`.
If `stop` is true then a STOP condition is generated at the end of the transfer.
Returns a `bytes` object with the data read.
.. method:: I2C.readfrom_into(addr, buf, stop=True)
Read into `buf` from the slave specified by `addr`.
The number of bytes read will be the length of `buf`.
If `stop` is true then a STOP condition is generated at the end of the transfer.
The method returns `None`.
.. method:: I2C.writeto(addr, buf, stop=True)
Write the bytes from `buf` to the slave specified by `addr`. If a
NACK is received following the write of a byte from `buf` then the
remaining bytes are not sent. If `stop` is true then a STOP condition is
generated at the end of the transfer, even if a NACK is received.
The function returns the number of ACKs that were received.
Memory operations
-----------------
Some I2C devices act as a memory device (or set of registers) that can be read
from and written to. In this case there are two addresses associated with an
I2C transaction: the slave address and the memory address. The following
methods are convenience functions to communicate with such devices.
.. method:: I2C.readfrom_mem(addr, memaddr, nbytes, \*, addrsize=8)
Read `nbytes` from the slave specified by `addr` starting from the memory
address specified by `memaddr`.
The argument `addrsize` specifies the address size in bits.
Returns a `bytes` object with the data read.
.. method:: I2C.readfrom_mem_into(addr, memaddr, buf, \*, addrsize=8)
Read into `buf` from the slave specified by `addr` starting from the
memory address specified by `memaddr`. The number of bytes read is the
length of `buf`.
The argument `addrsize` specifies the address size in bits (on ESP8266
this argument is not recognised and the address size is always 8 bits).
On WiPy the return value is the number of bytes read. Otherwise the
return value is `None`.
.. method:: I2C.writeto_mem(addr, memaddr, buf, \*, addrsize=8)
Write `buf` to the slave specified by `addr` starting from the
memory address specified by `memaddr`.
The argument `addrsize` specifies the address size in bits (on ESP8266
this argument is not recognised and the address size is always 8 bits).
On WiPy the return value is the number of bytes written. Otherwise the
return value is `None`.
Constants
---------
.. data:: I2C.MASTER
for initialising the bus to master mode
Availability: WiPy.