PIC24/dsPIC33 Digital Input Example
Objective
This example project demonstrates how to configure and use digital inputs on a PIC24F MCU. You will be shown how to configure a pin on the MCU, which is connected to a mechanical switch as a digital input. You will also configure another pin, connected to a Light-Emitting Diode (LED), as an output. The source code will be added to the project which reads the immediate value of the input switch and uses that value to drive the LED.
As a result of this lab:
- When the switch is pushed down, the LED will be on.
- When the switch is released, the LED will be off.
This project uses the PIC24F Curiosity Development Board. This board has two LEDs and two input switches:
- LED1: connected to pin RA9 (PORTA pin 9).
- LED2: connected to RA10.
- S1: connected to RC9.
- S2: connected to RC8.
We will first show you how to use MPLAB® Code Configurator (MCC) to generate code to configure RA9 (LED1) as an output pin, and RC9 (S1) as an input pin. You will then enter the code to drive LED1 high when S1 is pushed.
Materials
To follow along with this example, you will need the following software and hardware:
Software Tools
Hardware Tools
- PIC24F Curiosity Development Board (Microchip part number DM240004)
- USB Micro-B cable to connect the PIC24F Development Board to your computer
Procedure
Create the Project
After installing the software, connect the PIC24F Curiosity Development Board to a USB port on your computer. Create a new standalone project in MPLAB X IDE for a PIC124FJ128GA204. The PIC124FJ128GA204 is the microcontroller on the PIC24F Curiosity Development Board. When the project creation wizard asks for a hardware tool (Step 2 in the New Project window), select the PIC24F Curiosity Board as shown.
After the project has been created, the Projects tab in the upper-left corner of the IDE shows that the project has been created with no source or header files.
Open MCC
Open MCC under the Tools > Embedded menu of MPLAB X IDE.
MCC will place a Resource Management tab on the left-hand side of the IDE. Inside this tab, you will see a section for Project Resources and Device Resources. For each MCC-generated project, you will need to verify/modify the System Modules under the Project Resources window.
Set the Project Resources
There are three system elements that need attention:
- Interrupt Module: controls the MCU's interrupts.
- Pin Module: configures the I/O pins.
- System Module: selects and configures the clock source for the MCU.
Interrupt Module
This project does not use interrupts so this section will not be used.
System Module
The System Module allows the user to configure the MCU's clock and the Watchdog Timer (WDT), and make changes to the debug pin assignments. This feature of the PIC24F MCU has numerous options, which are typically modified to fit the needs of the application. MPLAB® Code Configurator (MCC) provides default settings if no changes are selected by the developer. For this lab, accept the default clock settings:
- 8 MHz Internal Free Running Oscillator with no Prescaler, but a 1:2 Postscaler (4 MHz Fosc)
- Watchdog Timer - disabled
- Unchanged debug pins
To verify the default settings, click on the System Module tab and verify the following selections have been made:
Pin Module
Click on the Pin Module in the Project Resources window. Three windows will open in the IDE:
- Pin Module Window
- Package View
- Grid View
The Pin Manager: Grid View window shows that pins RB1 and RB0 have been reserved as the programming pins.
We will now set the pin connected to LED1 (RA9) as an output and the pin connected to S1 (RC9) as an input. In the Grid View window, click on the output box under RA9 and the input box under RC9. The grid view will display the padlocks in green, indicating these pins have been configured for use.
- Ensure that RA9 is set as an output pin.
- Rename RA9 as LED1.
- Ensure that RC9 is set as an input pin.
- Rename RC9 as S1.
Generate Code
To generate the code, click the Generate button in the MCC window.
The Projects tab will show the source and header files created by MCC.
The main(void) function is located within the main.c file. The main(void) function calls the MCC-generated SYSTEM_Initialize() function before it enters the while(1) loop.
SYSTEM_Initialize() in turn calls PIN_MANAGER_Initialize() to configure the I/O pins. PIN_MANAGER_Initialize() loads the TRISA and TRISC registers with the values needed to set RA9 as an output pin and RC9 as an input pin.
Please consult the PIC24FJ128GA204 datasheet for the values used to configure TRISA and TRISC registers.
Modify the Program to Use the Value of S1 to Drive LED1
We will now modify main.c to drive RA9 (LED1) with the value of pin RC9 (S1). An inspection of the MCC-generated pin-manager.h header file, shows MCC has created several control functions for the I/O pins we have configured and named. Among these macros are LED1_SetLow, LED1_SetHigh, and S1_GetValue().
Make the following modifications to main.c:
main.c
#include "mcc_generated_files/mcc.h"
/*
Main application
*/
int main(void)
{
// initialize the device
SYSTEM_Initialize();
while (1)
{
if (S1_GetValue())
LED1_SetLow();
else
LED1_SetHigh();
}
return 1;
}
Build, Download, and Run the Code
To run the program on the development board, click on the Make and Program Device Main Project button 
. This will build the program into the Flash memory of the PIC® device. The output window of the IDE will tell you when the device has been programmed and the application is running.
After the board is programmed, neither LED1 nor LED2 will be on; they are both turned off.
Results
When S1 is pushed, LED1 will turn on. When S1 is released, LED1 will turn off.
