From the mbed microcontroller Handbook.

DigitalOut

/media/uploads/mbedofficial/digitalout_interfaces.png

The DigitalOut interface is used to configure and control a digital output pin.

Hello World!

Flash an LED

#include "mbed.h"

DigitalOut myled(LED1);

int main() {
    while(1) {
        myled = 1;
        wait(0.25);
        myled = 0;
        wait(0.25);
    }
}

API

API summary

DigitalOut	A digital output, used for setting the state of a pin
Functions
DigitalOut	Create a DigitalOut connected to the specified pin
write	Set the output, specified as 0 or 1 (int)
read	Return the output setting, represented as 0 or 1 (int)
operator=	A shorthand for write
operator int()	A shorthand for read

class DigitalOut : public Base

A digital output, used for setting the state of a pin

DigitalOut( PinName pin,
const char * name = NULL )

Create a DigitalOut connected to the specified pin

void write( int value )

Set the output, specified as 0 or 1 (int)

int read()

Return the output setting, represented as 0 or 1 (int)

DigitalOut& operator= ( int value )

A shorthand for write

operator int()

A shorthand for read

Interface

The DigitalOut Interface can be used on mbed pins p5-p30, and also on-board LED1-LED4

The DigitalOut Interface can be used to set the state of the output pin, and also read back the current output state. Set the DigitalOut to zero to turn it off, or 1 to turn it on.

Details

The pin output is 0v and 3.3v (0 and 1), and can source or sink a maximum of 40mA.

Examples

Alternative flashing

#include "mbed.h"

DigitalOut myled(LED1);

int main() {
    while(1) {
        myled = !myled;
        wait(0.25);
    }
}

Alternative flashing

#include "mbed.h"

DigitalOut red(p5);
DigitalOut green(p6);
DigitalOut blue(p7);

int main() {
    // red
    red = 1;
    green = blue = 0;
    wait(1);
    
    // green
    green = 1;
    red = blue = 0;
    wait(1);

    // white
    red = green = blue = 1;
}

Page history

Last modified 21 Jul 2010, by Dan Ros

No tags | 15 comments

15 comments on DigitalOut:

Jeff Bosch

# 05 Nov 2010

Just for fun, here's a "chase" program that shows how to use an array of DigitalOut objects to control the onboard LEDs for the LPC1768 contest board:

Code

#include "mbed.h"

DigitalOut leds[] = {(LED1), (LED2),(LED3)};

int main() {
    int i, previous;
    int numLeds = sizeof(leds)/sizeof(DigitalOut);
    while(1) {
        for (i = 0; i < numLeds; i++){
            if (i == 0) previous = (numLeds - 1);
            else previous = i - 1;
            
            leds[i] = 1;
            leds[previous] = 0;

            wait(0.2);
        }
    }
}

Bruce Matias

# 06 Nov 2010

THANKS Jeff Bosch

Jeff Bosch

# 06 Nov 2010

You're welcome - I hope it's useful to someone. I also created a notebook page that has a version that compares using DigitalOut and BusOut to achieve the same effect.

Zhen Ning Lim

# 03 Jan 2011

DigitalOut myled(LED1);

How to know which port is led 1 is connected?

Hendrik Lipka

# 03 Jan 2011

Zhen Ning Lim wrote:

DigitalOut myled(LED1);

How to know which port is led 1 is connected?

LED1 is the left-most LED of the mbed board - so there is no (external) port available.

Fevzi YAZGAN

# 06 Feb 2011

Knight Rider from Turkey:) this is the very first code of mine.

include "mbed.h"

DigitalOut leds[] = {(LED1), (LED2),(LED3),(LED4)};

int main() { int i,r; int numLeds = sizeof(leds)/sizeof(DigitalOut); i = -1; r = 1; while(1) { if (i > numLeds-2) r = -1; if (i == 0) r=1; i=i+r; if (i<numLeds) leds[i] = 1; if (((i>0)&&(r==1))||((i>-1)&&(r==-1))) leds[i-r] = 0; wait(0.1); } }

Aaron Goselin

# 06 Feb 2011

Fevzi YAZGAN wrote:

Lol nice Hello World program.

Fevzi YAZGAN

# 08 Feb 2011

Aaron Goselin wrote:

Fevzi YAZGAN wrote:

Lol nice Hello World program.

THNX

Eric Wertz

# 09 Jun 2011

What does read() return, the latched output value or the actual value of the pin?

yeaw chong tung

# 22 Sep 2011

Hi Jeff, i would want to know the meaning of command you used for the chasing LED.. what means by "size of" and why you use it? thank you..

Jeff Bosch

# 23 Sep 2011

Hi, Yeaw -

That's a standard C idiom that allows you to get the amount of memory allocated for an object. In this case, the number of elements in the array equals the size of the entire array divided by the size of a single element. By calculating the number of LEDs this way, I don't have to have storage for an explicit size constant, which makes life easier when adding or removing elements from the array.

Hope that helps.

Cheers,

Jeff

yeaw chong tung

# 25 Sep 2011

Hi, Jeff

sorry for my ignorant. when your i=0, is it leds[i]=leds[0]=LED(1) ? thank you so much for your concern.

Regard, Tung

- -

# 26 Oct 2011

Is it possible (e.g. by using asm) to use the Ethernet-Pins as DigitalOut?

Chris Styles

# 26 Oct 2011

Hi Kevin,

In short, no.

The reason is because those pins are not connected to the LPC1768, they are driven by the external Ethernet Phy (mounted on the underside of the mbed). These pins have been made special-function because of the layout and filtering requirements that Ethernet imposes.

Have a look at the schematics for the the mbed NXP LPC1768 in the handbook, all will become clear!

Hope that helps' Chris

Don DeGregori

# 23 Nov 2011

Maybe this info is known, but in case not: LED1 is connected to pin 18, (etc for the other 3 LEDS) on the mbed board.

LED1 = P1.18 LED2 = P1.20 LED3 = P1.21 LED4 = P1.23

donde

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