This lab uses interrupts. If you are looking for an example of using a PIC24F which polls the timer overflow flag, please refer to the"Programming a Microchip PIC24F Timer" example.

It is expected that after completing this lab, you will able to use MCC to set a timer period of any value on a 16-bit PIC MCU.

Information on how to download the software tools or acquire the development board can be found on the"Resources Needed for PIC24F Labs" page.

1

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 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 theNew Project window), select thePIC24F Curiosity Board as displayed below.

After the project has been created, theProjects tab in the upper-left corner of the IDE shows that the project has been created with no source or header files.

2

Open MCC

Open MCC under theTools > 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 theSystem Modules under theProject Resources window.

3

Set the Project Resources

There are three system elements which 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 section displays and controls the priority and the enable bit for each interrupt. This section will be reviewed after the Timer1 peripheral is configured (Step 6).

System Module

The System Module allows the user to configure the MCU's clock, 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 theSystem Module tab and verify the following selections have been made:

We will now set the pin connected to LED1 (RA9) as an output pin. In the Grid View window, click on the output box under RA9. 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.

4

Add the Timer to the List of Peripherals Being Used in the Application

From theDevice Resources section of the MCC Resource Management window, locate Timer1 (TMR1).

Double-click onTMR1 to add this peripheral to the resources available to the project.

5

Confgure Timer1 for Half-second Period with the Interrupt Enabled

With the F_osc set at 2 MHz, Timer1 will be unable to generate a half-second period as the 16-bit counter will overflow before half-second. To lengthen the period window for this timer, we will prescale the system clock by 64 to slow the timer down. Once the timer is slowed, we will be able to select the half-second timer period.

SelectTMR1 from the project window and select the following settings:

6

Verify the Priority of the Timer Interrupt

Select theInterrupt Module icon in theProject Resources window to verify that the Timer1 interrupt has been enabled.

7

Generate Code

To generate the code, click theGenerate button on the MCC window.

The projects tab will show the source and header files created by MCC.

Themain(void) is located within themain.c file.main(void) calls the MCC generatedSYSTEM_Initialize() function before it enters thewhile(1) loop.

SYSTEM_Initialize() in turn callsPIN_MANAGER_Initialize(),INTERRUPT_Initialize(), andTMR1_Initialize(). These functions initialize Timer1, set up the output pin and establish the interrupt writing to the device's function registers.

8

Modify the MCC-generated Code to Complete the Application

We will now modifymain.c.
An inspection of the MCC-generated header filepin-manager.h andtmr1.h shows MCC has created several control functions useful for our applications

pin-manager.h Function Prototype:

• LED1_toggle(); - changes the value of the I/O pin connected to the LED1

tmr1.h Function Prototypes:

• TMR1_Start(): starts the operation of Timer1
• TMR1_SetInterruptHandler(): registers a user defined function as the ISR for Timer1

Make the following modifications tomain.c

1. Insert the text#include "mcc_generated_files/mcc.h" near the top of the file
2. Create a functionvoid My_ISR(void); with one line of code LED1_Toggle();
3. InsertTMR1_Start andTMR1_SetInterruptHandler(My_ISR) into main.c as follows:

main.c

#include "mcc_generated_files/system.h"#include "mcc_generated_files/mcc.h"  //##### must be added #####void My_ISR(void)                     //#############  {    LED1_Toggle();   }int main(void){    SYSTEM_Initialize();    TMR1_SetInterruptHandler(My_ISR) ;  //##########    TMR1_Start();                       //##########    while (1)         {         }    return 1;}

8

Build, Download and Run the code

To run the program on the development board, click on theMake and Program Device Main Project button. This will build the program into the flash memory of the PIC^®. The output window of the IDE will tell you when the device has been programmed and the application is running.