Meadow.Foundation.ICs.IOExpanders.x74595

x74595
Status
Source code	GitHub
Datasheet(s)	GitHub
NuGet package

Shift registers offer the ability to increase the number of outputs on a microcontroller by using I2C or SPI interfaces. In the case of the 74xx595 series of shift registers, the SPI interface is used to output a series of bits that are then latched to the output pins of the chip.

This class allows Meadow to control the output pins on a 74HCT595 shift register using the SPI interface.

Note that when using this chip, care should be taken to ensure that the total output load of the chip does not exceed the current and thermal dissipation properties for the specific shift register being used.

Code Example

x74595 shiftRegister;

public override Task Initialize()
{
    Resolver.Log.Info("Initialize...");

    shiftRegister = new x74595(Device.CreateSpiBus(), Device.Pins.D00, 8);

    return base.Initialize();
}

public override async Task Run()
{
    shiftRegister.Clear(true);

    Resolver.Log.Info("Set Pin 3 to high");
    //turn on pin 3
    shiftRegister.WriteToPin(shiftRegister.Pins.GP3, true);

    Resolver.Log.Info("Set Pin 4 to high");

    //get the port for Pin4
    var port4 = shiftRegister.CreateDigitalOutputPort(shiftRegister.Pins.GP4, true, Meadow.Hardware.OutputType.OpenDrain);

    Resolver.Log.Info("Toggle pin 4");

    await Task.Delay(1000);
    port4.State = false;
    await Task.Delay(1000);
    port4.State = true;
    await Task.Delay(1000);

    Resolver.Log.Info("Raise all pins to high");
    while (true)
    {
        shiftRegister.Clear();

        foreach (var pin in shiftRegister.Pins.AllPins)
        {
            shiftRegister.WriteToPin(pin, true);
            await Task.Delay(50);
        }
    }
}

Sample project(s) available on GitHub

Wiring Example

To wire a 74HCT595 to your Meadow board, connect the following:

Class x74595

Provide an interface to connect to a 74595 shift register

Assembly: x74595.dll

View Source

Declaration

public class x74595 : IDigitalOutputController, IPinController, ISpiPeripheral

Implements:
Meadow.Hardware.IDigitalOutputController, Meadow.Hardware.IPinController, Meadow.Hardware.ISpiPeripheral

Properties

Pins

The pin definitions

View Source

Declaration

public x74595.PinDefinitions Pins { get; }

DefaultSpiBusSpeed

The default SPI bus speed for the device

View Source

Declaration

public Frequency DefaultSpiBusSpeed { get; }

SpiBusSpeed

The SPI bus speed for the device

View Source

Declaration

public Frequency SpiBusSpeed { get; set; }

DefaultSpiBusMode

The default SPI bus mode for the device

View Source

Declaration

public SpiClockConfiguration.Mode DefaultSpiBusMode { get; }

SpiBusMode

The SPI bus mode for the device

View Source

Declaration

public SpiClockConfiguration.Mode SpiBusMode { get; set; }

Fields

spiComms

SPI Communication bus used to communicate with the peripheral

View Source

Declaration

protected ISpiCommunications spiComms

Methods

CreateDigitalOutputPort(IPin, bool, OutputType)

Creates a new DigitalOutputPort using the specified pin and initial state

View Source

Declaration

public IDigitalOutputPort CreateDigitalOutputPort(IPin pin, bool initialState, OutputType outputType)

Returns

Meadow.Hardware.IDigitalOutputPort

Parameters

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

Clear(bool)

Clear the shift register buffer

View Source

Declaration

public void Clear(bool update = true)

Parameters

Type	Name	Description
System.Boolean	update	If true, send changes to the shift register

WriteToPin(IPin, bool)

Sets a particular pin's value.

View Source

Declaration

public void WriteToPin(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.

IsValidPin(IPin)

Checks whether or not the pin passed in exists on the chip.

View Source

Declaration

protected bool IsValidPin(IPin pin)

Returns

System.Boolean

Parameters

Type	Name
Meadow.Hardware.IPin	pin

GetPin(string)

Get pin from name

View Source

Declaration

public IPin GetPin(string pinName)

Returns

Meadow.Hardware.IPin: An IPin object

Parameters

Type	Name	Description
System.String	pinName	The pin name

Implements

• Meadow.Hardware.IDigitalOutputController
• Meadow.Hardware.IPinController
• Meadow.Hardware.ISpiPeripheral