Meadow.Foundation.ICs.IOExpanders.Mcp23xxx

Mcp23xxxx
Status
Source code	GitHub
NuGet package

The MCP chip family, referred to as MCP23XXX to represent the variations, is a digital I/O expander chip that uses I2C to communicate. It can be used to add additional digital input and output ports to Meadow and can be combined with up to eight MCP23xxx chips in total, providing 64 additional ports.

MCP23XXX chips are ubiquitous in the hardware world and is the typical interface chip for common I2C LCD backpacks, with the 74595 chip being the typical interface chip for SPI LCD backpacks.

MCP Chip Family

The MCP23XXX family includes the 8-bit MCP23008 and also includes the MCP23017, which is a 16-bit version of the MCP23008, offering 16 digital ports in total, and the MCP23S08 and MCP23S017 which are SPI versions of the MCP23008 and MCP23017, respectively.

Chip Addressing

The I2C address of the chip is configurable via the address pins and is in the binary form of 0100[A2][A1][A0], where A2, A1, and A0 refer to the three address pins on the chip:

For example, if all address pins were tied to ground, then the address of the chip would be 0100000 in binary, or 0x20 in hex, and 32 in decimal.

The I2C addresses can then be as follows, where 0 represents an address pin connected to ground, and 1 represents an address pin connected to 3.3V:

Address Header	A2	A1	A0	Resulting Hex Address	Resulting Decimal Address
0100	0	0	0	0x20	32
0100	0	0	1	0x21	33
0100	0	1	0	0x22	34
0100	0	1	1	0x23	35
0100	1	0	0	0x24	36
0100	1	0	1	0x25	37
0100	1	1	0	0x26	38
0100	1	1	1	0x27	39

Because there are 8 address possibilities, it's possible to put 8 MCP23XXX chips on a single I2C bus.

To make this simpler, when instantiating one of the MCP23XXX family of chip objects, there is a constructor overload that takes the address pin configurations instead of an address, so that Meadow.Foundation uses the appropriate address based on the pins, instead of requiring a pre-computed address.

Other Pins

In addition to the address pins, there are a number of other pins that must be connected up:

• Not Reset - The RESET pin is actually a "Not Reset." The line above "Reset" means "not." So unless that pin is pulled high (3.3V), the chip will reset itself at random times and you'll get connection errors.
• SCL and SDA - The SCL and SDA pins are the I2C clock and data pins and go to the SC and SD pins on the Meadow, respectively. Each of these should also generally be pulled high (3.3V) via a 4.7kΩ resistor. See the I2C guide for more information.
• INT - The INT pin is for interrupt notifications, and is only necessary when using the GPIO pins in input mode and you want an event raised when the input value changes.
• VSS and VDD - These go to ground and 3.3V power, respectively, and power the chip.

Code Examples

You can find code examples and links to sample projects for each of the MCP23XXX families and specific chips.

• MCP23x0x
  • MCP23008
  • MCP23009
  • MCP23S08
  • MCP23S09
• MCP23x1x
  • MCP23017
  • MCP23018
  • MCP23S17
  • MCP23S18

Class Mcp23xxx

Provide an interface to connect to a MCP23xxx port expander

Assembly: Mcp23xxx.dll

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Declaration

public abstract class Mcp23xxx : IDigitalInputOutputController, IDigitalInputController, IDigitalOutputController, ISpiPeripheral, II2cPeripheral, IDigitalInterruptController, IPinController

Derived:
Meadow.Foundation.ICs.IOExpanders.Mcp23x0x

Implements:
Meadow.Hardware.IDigitalInputOutputController, Meadow.Hardware.IDigitalInputController, Meadow.Hardware.IDigitalOutputController, Meadow.Hardware.ISpiPeripheral, Meadow.Hardware.II2cPeripheral, Meadow.Hardware.IDigitalInterruptController, Meadow.Hardware.IPinController

Properties

NumberOfPins

The number of IO pins available on the device

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Declaration

public abstract int NumberOfPins { get; }

DefaultSpiBusSpeed

The default SPI bus speed for the device

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Declaration

public Frequency DefaultSpiBusSpeed { get; }

SpiBusSpeed

The SPI bus speed for the device

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Declaration

public Frequency SpiBusSpeed { get; set; }

DefaultSpiBusMode

The default SPI bus mode for the device

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Declaration

public SpiClockConfiguration.Mode DefaultSpiBusMode { get; }

SpiBusMode

The SPI bus mode for the device

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Declaration

public SpiClockConfiguration.Mode SpiBusMode { get; set; }

DefaultI2cAddress

The default I2C address for the peripheral

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Declaration

public byte DefaultI2cAddress { get; }

Fields

_lock

object for using lock() to do thread sync

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Declaration

protected object _lock

Methods

GetAddressFromPins(bool, bool, bool)

Help method to get address from address pin configuration

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Declaration

public static byte GetAddressFromPins(bool pinA0, bool pinA1, bool pinA2)

Returns

System.Byte: The device address

Parameters

Type	Name	Description
System.Boolean	pinA0	State of A0 address pin - true if high
System.Boolean	pinA1	State of A1 address pin - true if high
System.Boolean	pinA2	State of A2 address pin - true if high

ResetMcp()

Reset the MCPxxxx expander Requires using a reset port

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Declaration

public void ResetMcp()

IsValidPin(IPin)

Checks if a pin exists on the Mcp23xxx

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Declaration

protected abstract bool IsValidPin(IPin pin)

Returns

System.Boolean

Parameters

Type	Name
Meadow.Hardware.IPin	pin

CreateDigitalOutputPort(IPin, bool, OutputType)

Creates a new DigitalOutputPort using the specified pin and initial state

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Declaration

public virtual IDigitalOutputPort CreateDigitalOutputPort(IPin pin, bool initialState = false, OutputType outputType = OutputType.OpenDrain)

Returns

Meadow.Hardware.IDigitalOutputPort: IDigitalOutputPort

Parameters

Type	Name	Description
Meadow.Hardware.IPin	pin	The pin representing the port
System.Boolean	initialState	Whether the pin is initially high or low
Meadow.Hardware.OutputType	outputType	The output type

CreateDigitalInputPort(IPin, ResistorMode)

Creates a new DigitalInputPort using the specified pin

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Declaration

public IDigitalInputPort CreateDigitalInputPort(IPin pin, ResistorMode resistorMode = ResistorMode.Disabled)

Returns

Meadow.Hardware.IDigitalInputPort: IDigitalInputPort

Parameters

Type	Name	Description
Meadow.Hardware.IPin	pin	The pin representing the port
Meadow.Hardware.ResistorMode	resistorMode	The port resistor mode

CreateDigitalInterruptPort(IPin, InterruptMode, ResistorMode)

Creates a new DigitalInputPort using the specified pin

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Declaration

public IDigitalInterruptPort CreateDigitalInterruptPort(IPin pin, InterruptMode interruptMode = InterruptMode.None, ResistorMode resistorMode = ResistorMode.Disabled)

Returns

Meadow.Hardware.IDigitalInterruptPort: IDigitalInterruptPort

Parameters

Type	Name	Description
Meadow.Hardware.IPin	pin	The pin representing the port
Meadow.Hardware.InterruptMode	interruptMode	The port interrupt mode
Meadow.Hardware.ResistorMode	resistorMode	The port resistor mode

CreateDigitalInterruptPort(IPin, InterruptMode, ResistorMode, TimeSpan)

Creates a new DigitalInputPort using the specified pin

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Declaration

public IDigitalInterruptPort CreateDigitalInterruptPort(IPin pin, InterruptMode interruptMode, ResistorMode resistorMode, TimeSpan debounceDuration)

Returns

Meadow.Hardware.IDigitalInterruptPort: IDigitalInterruptPort

Parameters

Type	Name	Description
Meadow.Hardware.IPin	pin	The pin representing the port
Meadow.Hardware.InterruptMode	interruptMode	The port interrupt mode
Meadow.Hardware.ResistorMode	resistorMode	The port resistor mode
System.TimeSpan	debounceDuration	The debounce duration

CreateDigitalInterruptPort(IPin, InterruptMode, ResistorMode, TimeSpan, TimeSpan)

Creates a new DigitalInputPort using the specified pin

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Declaration

public IDigitalInterruptPort CreateDigitalInterruptPort(IPin pin, InterruptMode interruptMode, ResistorMode resistorMode, TimeSpan debounceDuration, TimeSpan glitchDuration)

Returns

Meadow.Hardware.IDigitalInterruptPort: IDigitalInterruptPort

Parameters

Type	Name	Description
Meadow.Hardware.IPin	pin	The pin representing the port
Meadow.Hardware.InterruptMode	interruptMode	The port interrupt mode
Meadow.Hardware.ResistorMode	resistorMode	The port resistor mode
System.TimeSpan	debounceDuration	The debounce duration
System.TimeSpan	glitchDuration	The glitch duration - not configurable on Mcp23xxx

SetPortDirection(IPin, PortDirectionType)

Sets the direction of a port

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Declaration

public void SetPortDirection(IPin pin, PortDirectionType direction)

Parameters

Type	Name	Description
Meadow.Hardware.IPin	pin	The pin representing the port
Meadow.Hardware.PortDirectionType	direction	The port direction (input or output)

WriteToPort(IPin, bool)

Sets a particular pin's value. If that pin is not in output mode, this method will first set its mode to output.

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Declaration

public void WriteToPort(IPin pin, bool value)

Parameters

Type	Name	Description
Meadow.Hardware.IPin	pin	The pin to write to.
System.Boolean	value	The value to write. True for high, false for low.

ReadPort(IPin)

Gets the value of a particular port. If the port is currently configured as an output, this will change the configuration.

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Declaration

public bool ReadPort(IPin pin)

Returns

System.Boolean

Parameters

Type	Name
Meadow.Hardware.IPin	pin

WriteToPorts(byte)

Outputs a byte value across all of the pins by writing directly to the output latch (OLAT) register

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Declaration

public void WriteToPorts(byte mask)

Parameters

Type	Name
System.Byte	mask

ReadFromPorts(PortBank)

Reads a byte value from all of the pins. little-endian; the least significant bit is the value of GP0. So a byte value of 0x60, or 0110 0000, means that pins GP5 and GP6 are high.

View Source

Declaration

public byte ReadFromPorts(Mcp23xxx.PortBank bank = PortBank.A)

Returns

System.Byte: A little-endian byte mask of the pin values.

Parameters

Type	Name
Meadow.Foundation.ICs.IOExpanders.Mcp23xxx.PortBank	bank

ResetPin(IPin)

Sets the pin back to an input

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Declaration

protected void ResetPin(IPin pin)

Parameters

Type	Name
Meadow.Hardware.IPin	pin

GetPin(string)

Get Pin by name

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Declaration

public abstract IPin GetPin(string pinName)

Returns

Meadow.Hardware.IPin: IPin object if found

Parameters

Type	Name	Description
System.String	pinName	The pin name

Events

InputChanged

Raised when the value of any pin configured for input interrupts changes This provides raw port state data from the MCP23xxx It's highly recommended to prefer using the events exposed on the digital input ports instead.

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Declaration

public event EventHandler<IOExpanderInputChangedEventArgs> InputChanged

Event Type

System.EventHandler<Meadow.Foundation.ICs.IOExpanders.IOExpanderInputChangedEventArgs>

Implements

• Meadow.Hardware.IDigitalInputOutputController
• Meadow.Hardware.IDigitalInputController
• Meadow.Hardware.IDigitalOutputController
• Meadow.Hardware.ISpiPeripheral
• Meadow.Hardware.II2cPeripheral
• Meadow.Hardware.IDigitalInterruptController
• Meadow.Hardware.IPinController