mcp23008 — I2C input/output expander

The mcp23008 module enables the Kookaberry to use the MCP23008 I2C input/output expander chip. This chip allows digital inputs and outputs to be used beyond those already provided for on the Kookaberry. It is particularly useful for providing I2C serial control of external expander boards that have digital inputs and outputs.

Examples are keyboards, and digital sensing and control boards.

The data-sheet for the MCP23008 I/O multiplexer can be found at http://ww1.microchip.com/downloads/en/DeviceDoc/21919e.pdf

Class MCP23008

Example Usage:

# Sets the MCP23008 pins as outputs and then (with LEDs connected to all outputs) lights them in binary number patterns

import mcp23008                 # loads the mcp23008 module

# Set up the I2C bus
from machine import SoftI2C, Pin
i2c = SoftI2C(sda=Pin('P3A'), scl=Pin('P3B'))

i2cmux = mcp23008.MCP23008(i2c) # creates an instance of the mcp23008 named iomux
outbuf = bytearray(1)           # creates a single byte buffer
outbuf[0] = 0x00                # initialises the buffer for output
i2cmux.IODIR = outbuf           # IODIR sets the input/output configuration of the I/O pins

for i in range(0, 256):
    outbuf[0] = i
    i2cmux.OLAT = outbuf        # Transfer the binary pattern for i to the outputs
    time.sleep(0.1)             # Delay for visual observation of LEDs
outbuf[0] = 0                   # Reset the outputs on completion
i2cmux.OLAT = outbuf

MCP23008 Constructor

class mcp23008.MCP23008(i2c=None, address=0x20)

i2c should be a machine.SoftI2C object.

address is the I2C bus device hardware address. The MCP23008 I2C device has three hardware address pins allowing for up to 8 devices on the same I2C bus with addresses ranging from 0x20 (default) to 0x27 inclusive.

MCP23008 Properties

These properties provide access to the MCP23008 chip’s various registers.

property MCP23008.IODIR

Controls the direction of the data I/O.

When a bit is set, the corresponding pin becomes an input.

When a bit is clear, the corresponding pin becomes an output.

Assignment requires a serial buffer as the pattern is sent over the I2C bus

Usage:

buffer = bytearray(1)
# Setting IODIR
buffer[0] = pattern_byte
MCP23008.IODIR = buffer

# Read back IODIR
buffer = MCP23008.IODIR
print(buffer)

property MCP23008.IPOL

The IPOL register allows the user to configure the polarity on the corresponding GPIO port bits.

If a bit is set, the corresponding GPIO register bit will reflect the inverted value on the pin.

Usage is the same as IODIR using a serial buffer.

property MCP23008.GPPU

The GPPU register controls the pull-up resistors for the port pins.

If a bit is set and the corresponding pin is configured as an input, the corresponding port pin is internally pulled up with a 100 kohm resistor.

Usage is the same as IODIR using a serial buffer.

property MCP23008.GPIO

The GPIO register reflects the value on the port.

Reading from this register reads the port.

Writing to this register modifies the Output Latch (OLAT) register.

Usage is the same as IODIR using a serial buffer.

property MCP23008.OLAT

The OLAT register provides access to the output latches.

A read from this register results in a read of the OLAT and not the port itself.

A write to this register modifies the output latches that modify the pins configured as outputs.

Usage is the same as IODIR using a serial buffer.

MCP23008 Methods

These are convenience methods to deal with individual pins.

MCP23008.setPinDir(pin, direction)

Sets the pin (0 to 7) direction as an input (0) or as an output (1).

MCP23008.setPullupOn(pin)

Enables the 100 kilo ohm pull-up resistor on the designated pin (0 to 7).

MCP23008.setPullupOff(pin)

Disables the 100 kilo ohm pull-up resistor on the designated pin (0 to 7).

MCP23008.setPinLow(pin)

Sets the designated pin (0 to 7) to an output high (1) state.

MCP23008.setPinHigh(pin)

Sets the designated pin (0 to 7) to an output low (0) state.

MCP23008.readPin(pin)

Reads the designated pin’s (0 to 7) state, returning a 0 or a 1.