I2C Slave helper class

Use cases

This is a specific class for register-based I2C devices.

To learn how to use I2C bus, or how to make an I2C scanner, see the I2C section of Examples.

Class reference

class I2C_Slave(mcp, addr, force=False, speed=100000, reg_bytes=1, reg_byteorder='big')

EasyMCP2221’s I2C slave device.

I2C_Slave helper class allows you to interact with I2C devices in a more object-oriented way.

Usually you create new instances of this class using EasyMCP2221.Device.I2C_Slave() function. See examples section.

Parameters:

  • mcp (EasyMCP2221.Device) – MCP2221 connected to this slave

  • addr (int) – Slave’s I2C bus address

  • force (bool, optional) – Create an I2C_Slave even if the target device does not answer. Default: False.

  • speed (int, optional) – I2C bus speed. Valid values from 50000 to 400000. See EasyMCP2221.Device.I2C_speed().

  • reg_bytes (int, optional) – How many bytes is the register, position or command to send (default 1 byte).

  • reg_byteorder (str, optional) – Byte order of the register address. ‘little’ or ‘big’. Default ‘big’.

Raises:

RuntimeError – If the device didn’t acknowledge.

Examples

You should create I2C_Slave objects from the inside of an EasyMCP2221.Device:

>>> import EasyMCP2221
>>> mcp = EasyMCP2221.Device()
>>> eeprom = mcp.I2C_Slave(0x50, reg_bytes = 2)
>>> eeprom
EasyMCP2221's I2C slave device at bus address 0x50.

Or in a stand-alone way:

>>> import EasyMCP2221
>>> from EasyMCP2221 import I2C_Slave
>>> mcp = EasyMCP2221.Device()
>>> eeprom = I2C_Slave.I2C_Slave(mcp, 0x50, reg_bytes = 2)

Note

MCP2221 firmware exposes a subset of predefined I2C operations, but does not allow I2C primitives (i.e. start, stop, read + ack, read + nak, clock bus, etc.).

is_present()

Check if slave is present.

Perform a read operation (of 1 bytes length) to the slave address and expect acknowledge.

Returns:

True if the slave answer, False if not.

Return type:

bool

read(length=1)

Read from I2C slave.

See EasyMCP2221.Device.I2C_read().

Parameters:

length (int) – How many bytes to read. Default 1 byte.

Returns:

bytes string

Raises:

RuntimeError – if the I2C slave didn’t acknowledge or the I2C engine was busy.

read_register(register, length=1, reg_bytes=None, reg_byteorder=None)

Read from a specific register, position or command.

Sequence:

  • Start

  • Send device I2C address + R/W bit 0

  • Send register byte, memory position or command

  • Repeated start

  • Send device I2C address + R/W bit 1

  • Read length bytes

  • Stop

See EasyMCP2221.Device.I2C_read() for more information.

Parameters:

  • register (int) – Register to read, memory position or command.

  • length (int, optional) – How many bytes is the answer to read (default read 1 byte).

  • reg_bytes (int, optional) – How many bytes is the register, position or command to send (default is defined in the class constructor).

  • reg_byteorder (str, optional) – Byte order of the register address. ‘little’ or ‘big’. Default is defined in the class constructor.

Returns:

bytes string

Examples

Read from a regular i2c device, register 0x0D:

>>> bme.read_register(0x0D)
>>> b'ÿ'

Read 10 bytes from I2C EEPROM (2 bytes memory position):

>>> eeprom = mcp.I2C_Slave(0x50, reg_bytes = 2)
>>> eeprom.read_register(2000, 25)
>>> b'en muchas partes hallaba '
write(data)

Write to I2C slave.

See EasyMCP2221.Device.I2C_write() for more information.

Parameters:

data (bytes) – Data to write. Bytes, int from 0 to 255, or list of ints from 0 to 255.

Raises:

RuntimeError – if the I2C slave didn’t acknowledge or the I2C engine was busy.

write_register(register, data, reg_bytes=None, reg_byteorder=None)

Write to a specific register, position or command.

Sequence:

  • Start

  • Send device I2C address + R/W bit 0

  • Send register byte, memory position or command

  • Repeated start

  • Send device I2C address + R/W bit 0

  • Write data

  • Stop

See EasyMCP2221.Device.I2C_write() for more information.

Parameters:

  • register (int) – Register to read, memory position or command.

  • data (bytes) – Data to write. Bytes, int from 0 to 255, or list of ints from 0 to 255.

  • reg_bytes (int, optional) – How many bytes is the register, position or command to send (default is defined in the class constructor.).

  • reg_byteorder (str, optional) – Byte order of the register address. ‘little’ or ‘big’. Default is defined in the class constructor.

Examples

Set PCF8591’s DAC output to 255. Command 0bx1xxxxxx.

>>> pcf.write_register(0b01000000, 255)

Write a stream of bytes to an EEPROM at position 0x1A00 (2 bytes memory position):

>>> eeprom = mcp.I2C_Slave(0x50, reg_bytes = 2)
>>> eeprom.write_register(0x1A00, b'Testing 123...')
>>> eeprom.read_register(0x1A00, 14)
b'Testing 123...'