8-Bit Digital Input

This project demonstrates how to read a digital input pin on a microcontroller and control a Light Emitting Diode (LED) based on the state of a momentary switch connected to the digital input.

proj2.png

Step by Step Instructions

Using the MPLAB® Code Configurator (MCC) simplifies the setup for the various registers within the device to create a digital input. To demonstrate how to get started, this project monitors a momentary switch connected to pin RB4 that is enabled as a digital input using an internal pull-up. The code will light an LED connected to RA4, enabled as a digital output when the switch is pressed.

proj2pic.png

The project uses:

  • PIC16F18875
  • HPC Curiosity Board
  • MPLAB X IDE
  • MPLAB Code Configurator (MCC) plug-in
  • MPLAB XC8 Compiler

To follow along with these steps, MPLAB X IDE should be open and the HPC Curiosity Board connected to the computer through a USB cable.

1

Create a new standalone project in MPLAB X for a PIC16F18875.

If this is your first time creating an MPLAB X project, please visit the "Create a Standalone Project" page to follow a step-by-step instruction on how to do this.

2

Open MCC under the Tools > Embedded menu of MPLAB X IDE.

mcclaunch.png

3

Select the peripherals for your project. For this project, the following peripherals need to be selected:

  • System Module
  • Interrupt Module
  • Pin Module

The System Module, Interrupt Module, and the Pin Module will all be automatically included when you launch the MCC. The result should look like the picture below:

proj1per.png

4

Open the Pin Manager: Grid View. Next, click on the PORTA - 4 blue lock symbol in the Output row. This will change it to locked and turn it green in color. Also, click on the PORTB - 4 blue lock symbol in the Input row to change it to green and locked. Check that the Reset is blue and unlocked. Click on it if it is set to green and locked. This adds the RA4 and RB4 I/O pins to the project. It should look like the picture below when completed:

proj2io2.png

5

Close the Pin Manager: Grid View. Then, click on the Pin Module in the Project Resources area.

gpio.png

The center section should show RA4 and RB4 listed on the I/O chart.

  1. RB4 will be the input that will read the switch. The Weak Pull-Up (WPU) box is checked.
  2. RA4 will be an output and control the LED. Click on the Output box to make the pin an output.

Change the names of the pins to LED for RA4 and Switch for RB4.

proj2ioset.png

6

Next, the system needs to be set up. Click on System Module in the Project Resources list. It should be highlighted in blue when selected.

system.png

In this section, the oscillator settings and the configuration settings are selected.

Oscillator

  1. Select the HFINTOSC from the Oscillator Select drop-down menu.
  2. Select the 4MHz selection from the HF Internal Clock drop-down menu.
  3. Select Clock Divider value of 4.

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

oscillator.png

Also, make sure the Low-voltage Programming Enable mode is selected at the bottom of the System Module screen.

lvp.png

7

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

generate.png

8

The project will now have both generated Header Files and Source Files. It should also have a generated a main.c file.

proj2files.png

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

mainfile.png

9

Add the following code to the end of the main.c file:

void main(void)
{
    // initialize the device
    SYSTEM_Initialize();

    while (1)
    {
        // Add your application code

        if (Switch_GetValue() == 0)
            {
            LED_SetHigh();
            }
        else
            {
            LED_SetLow();
            }

    }
}

The Switch_GetValue(), LED_SetHigh() and, LED_SetLow() are #define's and macros that were generated by the MCC. Their definitions are located in the pin_manager.h file.

#define Switch_GetValue()           PORTBbits.RB4
#define LED_SetHigh()            do { LATAbits.LATA4 = 1; } while(0)
#define LED_SetLow()             do { LATAbits.LATA4 = 0; } while(0)

This is a simple example of how the MCC generates a library of useful functions to make creating project code much easier and quicker.

10

Click on the Build Project icon (the hammer) to compile the code. You should see a BUILD SUCCESSFUL message in the output window.

Main_Build_Project.png
BUILD SUCCESSFUL

11

Make sure your project has the Curiosity Board selected and the USB cable is connected to the board.

Click on Make and Program Device. 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/Verify complete" message and the D2 LED connected to RA4 will be lit when the S1 button on the center on the HPC Curiosity Board is pressed.

Main_Program_Target_Project.png

Output Window:

Connecting to Starter Kit on Board...

Currently loaded firmware on Starter Kit on Board
Firmware Suite Version.....01.54.00
Firmware type..............Enhanced Midrange

Target voltage detected
Target device PIC16F18875 found.
Device Revision ID = 2002

Device Erased...

Programming...

The following memory area(s) will be programmed:
program memory: start address = 0x0, end address = 0x7ff
configuration memory
Programming/Verify complete
proj2final.png

When the project is loaded you will be able to press the switch and see the LED light up.

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 may 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

12

The project can be closed in the MPLAB X IDE. 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 2 Files
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