Page 126 - ARM Based Microcontroller Projects Using MBED

112 7. USING THE Mbed WITH SIMPLE PROJECTS

/****************************************************************

EXTERNAL BUTTON WITH LED
========================
In this program an external button is conencted to GPIO pin PC_0
of teh Nucleo-F411RE development board. This button controls the
on-board User LED such that when the button is pressed the LED
turns ON
Author: Dogan Ibrahim
Date : August 2018
File : EXTbutton
******************************************************************/
#include "mbed.h"
DigitalOut led(LED1); // LED is output
DigitalIn button(PC_0); // Button is input
int main()
{
while(1) // Do forever
{
if(button == 0) // If button pressed
led = 1; // LED ON
else
led = 0; // LED OFF
}
}

FIG. 7.53 Program listing.

PullNone: No pull-up/pull-down resistors
OpenDrain: GPIO pin on open-drain mode
The earlier modes can either be specified during the declaration of the DigitalIn
statement,or later as shown in the following:
DigitalIn button(PC_0, PullUp);
or as:
DigitalIn button(PC_0);
button.mode(PullUp);

7.13.9 Suggestions for Additional Work
Modify the circuit in Fig. 7.50 by removing the external pull-up resistor and enable the in-
ternal pull-up resistor on port pin PC_0 in the program as shown in Fig. 7.53.