Remarks

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, 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:

Characteristic	Locus
Inheritance	System.Object > x74595
Namespace	Meadow.Foundation.ICs.IOExpanders
Assembly	x74595.dll

Syntax

public class x74595 : IDigitalOutputController

Constructors

x74595(IMeadowDevice, ISpiBus, IPin, Int32)

Creates a new ShiftRegister 74595 object

Declaration

public x74595(IMeadowDevice device, ISpiBus spiBus, IPin pinChipSelect, int pins = 8)

Parameters

Type	Name	Description
IMeadowDevice	device	The device conneced to the shift register
ISpiBus	spiBus	SpiBus object
IPin	pinChipSelect	The chip select pin
System.Int32	pins	Number of pins in the shift register (should be a multiple of 8 pins).

Properties

Pins

The pin definitions

Declaration

public x74595.PinDefinitions Pins { get; }

Property Value

Type	Description
x74595.PinDefinitions

Methods

Clear(Boolean)

Clear the shift register buffer

Declaration

public void Clear(bool update = true)

Parameters

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

CreateDigitalOutputPort(IPin, Boolean, OutputType)

Creates a new DigitalOutputPort using the specified pin and initial state

Declaration

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

Parameters

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

Returns

Type	Description
IDigitalOutputPort

GetPin(String)

Get pin from name

Declaration

public IPin GetPin(string pinName)

Parameters

Type	Name	Description
System.String	pinName	The pin name

Returns

Type	Description
IPin	An IPin object

IsValidPin(IPin)

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

Declaration

protected bool IsValidPin(IPin pin)

Parameters

Type	Name	Description
IPin	pin

Returns

Type	Description
System.Boolean

WriteToPin(IPin, Boolean)

Sets a particular pin's value.

Declaration

public void WriteToPin(IPin pin, bool value)

Parameters

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