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.
Constructors¶
-
class
machine.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¶
-
I2C.deinit()¶ Turn off the I2C bus.
Availability: WiPy.
-
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.
-
I2C.start()¶ Generate a START condition on the bus (SDA transitions to low while SCL is high).
Availability: ESP8266.
-
I2C.stop()¶ Generate a STOP condition on the bus (SDA transitions to high while SCL is high).
Availability: ESP8266.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.