DigitalOut

Table of Contents

  1. Hello World!
  2. API
  3. Interface

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

Hello World!

» Import this program
DigitalOut_HelloWorld - main.cpp

#include "mbed.h"

DigitalOut myled(LED1);

int main() {
    while(1) {
        myled = 1;
        wait(0.2);
        myled = 0;
        wait(0.2);
    }
}

API

API summary

» Import latest build into a program
mbed - DigitalOut Class Reference

Public Member Functions

  DigitalOut (PinName pin)
  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 any pin with a blue label, and also with the on-board LEDs (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.

/media/uploads/chris/pinout-thumbnails.jpg
See the Pinout page for more details


Ask a question
Last modified 22 Feb 2013, by user Emilio Monti. 20 comments

20 comments:

user 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:

#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);
        }
    }
}
user Bruce Matias
06 Nov 2010

THANKS Jeff Bosch

user 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.

user Zhen Ning Lim
03 Jan 2011

DigitalOut myled(LED1);

How to know which port is led 1 is connected?

user Hendrik Lipka
03 Jan 2011

user 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.

user Fevzi YAZGAN
06 Feb 2011

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

  1. 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); } }

user Aaron Goselin
06 Feb 2011

user Fevzi YAZGAN wrote:

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); } }

Lol nice Hello World program.

user Fevzi YAZGAN
08 Feb 2011

user Aaron Goselin wrote:

user Fevzi YAZGAN wrote:

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); } }

Lol nice Hello World program.

THNX

user Eric Wertz
09 Jun 2011

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

user 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..

user 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

user 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

user BlazeX
26 Oct 2011

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

user 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

user 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

» Show archived comment by ashwini
user Ashwini DS
21 Sep 2012
user Leo Browne
25 Jan 2013

Just to avoid confusion for anyone reading this, this is incorrect. While LED1 is connected to P1.18, this is not pin 18 on the mbed board. P1.18 means port 1, bit 18. p18 on the board is connected to P0.26. These ports (P0.x, P1.x, etc.) are internal to the LPC1768 on the board, and only a select few are actually broken out to pins on the DIP package.

EDIT: This is off topic for this page, but for more information on what each pin is connected to, see this document:

http://mbed.org/media/uploads/chris/mbed-005.1.pdf

user Don DeGregori wrote:

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

user Erik Olieman
25 Jan 2013

Euhm, so it is correct what he says, it is connected to P1.18, he never claims it is connected to p18. In the compiler you can address it with P1_18 (or just LED1).

Edit: my bad, didnt correctly read his post, you are right :)

user Leo Browne
26 Jan 2013

I think when he refers to "pin 18 on the mbed board", it's safe to say he's talking about p18. Yes, he's right when he says the LEDs are connected to P1.18, P1.20, etc, but again, when he says pin 18 on the mbed board, it's misleading.

user Erik Olieman wrote:

Euhm, so it is correct what he says, it is connected to P1.18, he never claims it is connected to p18. In the compiler you can address it with P1_18 (or just LED1).

user hemantha gowda
03 May 2013

user Leo Browne wrote:

I think when he refers to "pin 18 on the mbed board", it's safe to say he's talking about p18. Yes, he's right when he says the LEDs are connected to P1.18, P1.20, etc, but again, when he says pin 18 on the mbed board, it's misleading.

user Erik Olieman wrote:

Euhm, so it is correct what he says, it is connected to P1.18, he never claims it is connected to p18. In the compiler you can address it with P1_18 (or just LED1).

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