Timer 0 - Delay Using Interrupt

The Timer 0 module is a 8-bit timer/counter within most PIC® MCU devices. The Timer 0 can also trigger an interrupt when it overflows. This project will create a blinking LED based on a Timer 0 Interrupt Delay.

proj1.png

Step by Step Instructions

Using the MPLAB® Code Configurator (MCC), this project generates the code to blink an LED using a hardware Timer 0 Interrupt to generate the delay between the On and Off state.

proj1pic.png

The project uses:

PICDEM Lab II Connections:

  • Connect 5 V and Gnd to the power bus of the protoboard.
  • Connect 5 V to the Vdd pin of the PIC16F1508
  • Connect Gnd to the Vss pin of the PIC16F1508
  • Connect a wire from the RA2 pin (pin 17) to the breadboard Row 23
  • Connect a wire from the ground bus to breadboard Row 27
  • Connect the LED Anode to breadboard Row 23
  • Connect the LED Cathode to breadboard Row 24
  • Connect a 330 ohm resistor between Row 24 and Row 27

To follow along with these steps, MPLAB X should be open and the Programmer/Debugger connected to both the computer and the Development Board. The setup was described in the Setup and Installation section of this training module. You should see a screen similar to the one below to move on to step 1.

mplabx.png

1

Create a new "Stand-Alone" project in MPLAB X for a PIC16F1508. Instructions are below if this is your first project.

2

Open the MPLAB Code Configurator under the Tools -> Embedded menu of MPLAB X IDE.

mcclaunch.png

3

Select the peripherals for your project.
In this first project these peripherals need to be selected:

  • System Module
  • Interrupt Module
  • Pin Module
  • TMR0

The System Module, Interrupt Module and the Pin Module will all be automatically included when you launch the MCC. TMR0 needs to be added from the Device Resources area. Just click on the Timer category and then double click on the Timer 1 to add it to the project. The result should look like the picture below:

proj6per2.png

4

Open the Pin Manager and then click on the PORTA pin 2 (RA2) Output blue lock symbol. It should turn green and adds RA2 I/O pin to the project. Also make sure the Reset pin has the blue lock shown. If it's green then click on the green lock to make it blue. This will make the Reset internal. It should look like the picture here when completed:

proj4io2.png

5

Close the Pin Manager and then click on the Pin Module selection in the Project Resources section.

gpio.png

The center screen should show RA2 listed on the I/O chart. Click on the output box to make the pin an output (if not checked) and make sure Analog and WPU are not checked (click on them to uncheck them).

proj1ioset.png

6

The System needs to be setup next. Click on the System name in the Project Resources list.

system.png

The System section will appear. In this section the oscillator settings and the configuration settings are selected.

Oscillator

  1. Select the INTOSC from the drop down menu for the System Clock Select.
  2. Select the 1MHz_HF selection from the Internal Clock drop down menu.

This will enable the internal 1 MHz internal oscillator as the system clock.

oscillator.png

Configuration

Each configuration setting can be changed under the Register tab of the System window. Match the selections shown here.

config1.png
config2.png

7

The Timer0 needs to be setup. Click on the TMR0 label in the Project Resources menu to make the Timer0 setup screen appear.

tmr0.png

The Timer 0 will be driven by the instruction clock which was setup in step 5.

  1. Check the Enable Timer box.
  2. Set Clock Source to Fosc/4 (This is the instruction clock).
  3. Set the Prescaler box to 1:256.
  4. Set the Timer Period to 250 ms (The Reload Value should automatically adjust).
  5. Check the Enable Timer Interrupt box (This will add the Interrupt Manager to the Project Resources).

The window should look like below after the setup:

timer0setup.png

8

The Interrupt Manager should be reviewed. Click on the Interrupt Manager label in the Project Resources menu to view the setup screen.

intman2.png

The Timer 0 will be shown as an interrupt source which was setup in step 7.

Note the message:
Please remember to enable the Peripheral and Global Interrupts in your code!

This will be setup in the main.c file of the project code.

9

Click on the Generate Code button to have the MCC create the software libraries for this project.

generate.png

10

The project will now have both generated Header Files and Source Files. It should also have a generated main.c file.
Note: MCC may offer to generate a main.c file. Click YES to allow it to complete that task.

proj6files2.png

Double click on the main.c file to open it up in the editor window.

mainfile.png

11

There are two files that need to be modified for this project: main.c and tmr0.c. These are the main code file and the timer 0 code file. Each are modified as described below.

main.c

The main.c file requires a few lines to be uncommented for the interrupt to work properly. To enable the interrupt to work, Global Interrupts and the Peripheral Interrupts need to be enabled. The MCC already has the control commands in the default main.c file, they are just commented out with two forward slashes (//). The forward slashes need to be removed to enable these lines of code.

    // Enable the Global Interrupts
    INTERRUPT_GlobalInterruptEnable();

    // Enable the Peripheral Interrupts
    INTERRUPT_PeripheralInterruptEnable();

The main loop doesn't require any additional code beyond the default while(1) loop. The Interrupt Service Routine will handle the changing of the I/O pin.

while (1)
    {
        // Add your application code

    }
maincode6.png

tmr0.c

The tmr0.c file contains the Interrupt Service Routine that will run when the interrupt occurs. This is where a function to toggle the LED pin is entered. The function used is the IO_RA2_Toggle() macro that is created by the MCC and placed in the pin_manager.h file. This IO_RA2_Toggle() is added to the Interrupt Service Routine as shown below.

t0isr.png

In addition to the Interrupt Service Routine modification, the tmr0.c file also needs to know where the definitions are for the toggle function. By adding the line #include "mcc.h to the tmr0.c file, the definitions generated by MCC can be compiled with the tmr0.c file without errors. The screen capture below shows the proper place to add any #include statements:

t0isrinc.png

12

Click on the Build Project Icon (Hammer) to compile the code and you should see a BUILD SUCCESSFUL message in the output window of MPLAB X.

Main_Build_Project.png
BUILD SUCCESSFUL (total time: 325ms)

13

Make sure your project has the programming tool selected (Part of Step 1 above) and connect power to your development board.

The PICkit 3 has limited power capability so we recommend you power the board separately.
The ICD 3 can power a development board, but for simplicity we recommend you power the board separately.
The RealICE cannot power the development board so powering the board separately is required.

Click on the Make and Program Device icon. This will build the project again and launch the programmer. In the output window you should see a series of messages and if successful it will end with a Programming and Verify Successful message.

Main_Program_Target_Project.png

Output Window:

Connecting to MPLAB PICkit 3...

Currently loaded firmware on PICkit 3
Firmware Suite Version.....01.41.06
Firmware type..............Enhanced Midrange

Target voltage detected
Target device PIC16F1508 found.
Device ID Revision = 2

The following memory area(s) will be programmed:
program memory: start address = 0x0, end address = 0x5f
configuration memory

Device Erased...

Programming...
Programming/Verify complete



The RA2 LED will blink at a 250 millisecond rate on then off. The picture below shows the LED caught in the lit position but the application will blink continuously.
ra2lit.jpg

If it's the first time the programmer is connected to the board, the programming tool may need to download the proper operating firmware for the exact device. You make see a series of processes if this occurs. This should only happen once.

Downloading Firmware…
Downloading bootloader
Bootloader download complete
Programming download…
Downloading RS…
RS download complete
Programming download…
Downloading AP…
AP download complete
Programming download…
Firmware Suite Version…..01.34.11
Firmware type…………..Enhanced Midrange

14

The project can be closed in MPLAB X. The project is saved automatically when it is built but any changes to files or configuration may ask to be saved before the project is closed. The project can be closed under the File Menu>Close Project

closeproject.png

Download

If you have any problems with your project, the completed MPLAB X project file can be downloaded from the link below:

File Download
Installation
Instructions
Windows Linux Mac OSX
Project 6 Files

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