8-bit ADC Auto Convert Using Timer6

Last modified by Microchip on 2023/11/09 09:12


The Core Independent Peripherals (CIPs) within the latest PIC® 8-bit microcontrollers offer the opportunity to perform hardware functions without the Central Processing Unit (CPU) core running any code. This can be extremely useful for embedded projects that need to perform certain tasks without interruption from the main application. This simple example shows how to set up and use the Analog-to-Digital Converter (ADC) peripheral and Timer6 control to independently control an analog-to-digital conversion. The separate hardware then notifies the main application of an updated value through an ADC Interrupt. The accompanying image shows the block diagram of the project. As you can see, the control runs completely independently from the CPU.

ADC Project Block Diagram

Exercise Files

Return to top

Connection Diagram

The Curiosity board has four LEDs prewired to the I/O pins shown in the accompanying table. This project controls three of the four LEDs.

Hardware FunctionPinSetting
IO_LED_D4RA5 (2)Output
IO_LED_D5RA1 (18)Output
IO_LED_D6RA2 (17)Output
IO_LED_D7RC5 (5)Output

Curiosity LEDs

1. Create a Project

Create a new project and select the PIC16F1619 along with the Curiosity Board and MPLAB® XC8 compiler. 

Return to top

2. Launch MCC

Open the MPLAB Code Configurator (MCC) under the Tools > Embedded menu of MPLAB X IDE.

MCC Launch

Return to top

3. System Setup

From Project resources, choose System Module to open the System Setup window within MCC.

  1. In the Oscillator settings, make sure you select INTOSC.
  2. Select the System Clock FOSC.
  3. Set the Internal Clock to 4MHz_HF.
  4. Check the PLL Enabled box.
  5. The Curiosity Development Board uses a Programmer/Debugger On Board (PKOB) and uses a Low-Voltage Program method to program the MCU, therefore we must enable low-voltage programming by checking the Low-voltage programming Enable box.

System Setup

Return to top

4. Timer6 Setup

Add the TMR6 peripheral to the project from the Device Resources area of MCC. To do that, scroll down to the Timer entry and expand the list by clicking on the arrow. Now, double-click on the TMR6 entry to add it to the Project Resources list. Then, click on the TMR6 to open the Timer6 configuration setup screen.

Timer 6 Setup

  1. Check the Enable Timer box.
  2. Select Clock Source LFINTOSCPostscaler 1:1Prescaler 1:32.
  3. Set Timer period value to 100.129 ms.
  4. Set External Reset Source to T6IN, and Control mode setting to Roll over pulse.
  5. Set Start/Reset Option to Software Control (this will inhibit hardware reset of timer).
  6. Leave the Enable Timer Interrupt box unchecked.

Return to top

5. ADC Setup

Add the ADC peripheral to the Project Resources from the Device Resources area. Scroll down to the ADC entry and expand the list. Now, double-click on the ADC entry to add it to the Project Resources list.

Click on the ADC and the Setup window will show up. Follow the steps below:

  1. Check the Enable ADC box.
  2. Select Clock Source: FRC.
  3. Set Result Alignment: right.
  4. Set Postitive Vref is VDD.
  5. Set Auto-conversion Trigger to TMR6_postscaled.
  6. Check the Enable ADC Interrupt box.

ADC Setup

Return to top

6. Pin Manager Setup

The potentiometer labeled POT1 and LEDs labeled D4-D7 on the Curiosity Development Board need to be connected to the proper pins in software to match the hardware. This is easily done in the Pin Manager by clicking on the blue lock to change it to green.

  1. Click on RC0 in ADC row.
  2. Click on RA1RA2RA5, and RC5 in the GPIO Output row.


I/O Setup

Assign Custom Names

Click on the Pin Module in the project resources area.

  1. Uncheck WPU (Weak Pull-up) box for all pins.
  2. Uncheck Analog box for all but RC0.
  3. Rename RC0 Custom Name to "POT1_AN4".
  4. Rename RA1 Custom Name to "D5_RA1".
  5. Rename RA2 Custom Name to "D6_RA2".
  6. Rename RA5 Custom Name to "D4_RA5".
  7. Rename RC5 Custom Name to "D7_RC5".

Pin Name Setup

Return to top

7. Generate Driver Code

Click on the Generate button in the Project Resources of the MCC screen to have the MCC create the drivers and a base main.c file for the project.

Return to top

8. adc.c

To control the LEDs based on the Analog-to-Digital conversion, the Interrupt Service Routine (ISR) needs to be updated in the adc.c file. The Timer6 overflow starts the ADC conversion and then, when the conversion is complete, the ADC interrupt will run the adc.c file ISR.

These lines need to be added to the ADC_ISR function in the adc.c file. This will store the ADC result in a variable adval then light the LEDs based on that value.

adc_result_t adval = ADC_GetConversionResult();
D4_RA5_LAT = (adval > (1024*1)/5); // LEDD4 on if adval>204
D5_RA1_LAT = (adval > (1024*2)/5); // LEDD5 on if adval>409
D6_RA2_LAT = (adval > (1024*3)/5); // LEDD6 on if adval>614
D7_RC5_LAT = (adval > (1024*4)/5); // LEDD7 on if adval>819

The code is added to the adc.c file ADC_ISR function as shown below.

void ADC_ISR(void)
    adc_result_t adval = ADC_GetConversionResult();
    D4_RA5_LAT = (adval > (1024*1)/5); // LEDD4 on if adval>204
    D5_RA1_LAT = (adval > (1024*2)/5); // LEDD5 on if adval>409
    D6_RA2_LAT = (adval > (1024*3)/5); // LEDD6 on if adval>614
    D7_RC5_LAT = (adval > (1024*4)/5); // LEDD7 on if adval>819

    // Clear the ADC interrupt flag
    PIR1bits.ADIF = 0;

Return to top

9. main.c

The generated main.c file needs two lines uncommented and one added for this project.
First, the Global Interrupt and Peripheral Interrupt Enable lines need to be uncommented by removing the // in front of these lines to enable interrupts.

// Enable the Global Interrupts
// Enable the Peripheral Interrupts

    // When using interrupts, you need to set the Global and Peripheral Interrupt Enable bits
    // Use the following macros to:

    // Enable the Global Interrupts

    // Enable the Peripheral Interrupts

    // Disable the Global Interrupts

    // Disable the Peripheral Interrupts

The ADC conversion command line; ADC_StartConversion(POT1_AN4) is added to main.c before the continuous while(1) loop. This starts the ADC and then does nothing while looping yet the ADC runs in the background updating the LEDs based on the position of the potentiometer.

    while (1)
        // Add your application code

 End of File

Return to top

10. Build Project

Click on Build Project (hammer icon) to compile the code and you will see a "BUILD SUCCESSFUL" message in the output window of MPLAB X within several seconds of processing time.


BUILD SUCCESSFUL (total time: 8s)

Return to top

11. Program Device

Make sure your Curiosity Board is connected to the USB port. Then, click on Make and Program Device. This will build the project again and launch the programmer built into the Curiosity Board. In the Output window, you should see a series of messages and when successful it will end with a "Programming and Verify Successful" message.


Output Window:

Connecting to MPLAB Starter Kit on Board...

Currently loaded firmware on Starter Kit on Board
Firmware Suite Version.....01.41.07
Firmware type..............Enhanced Midrange

Target detected
Device ID Revision = 2004

The following memory area(s) will be programmed:
program memory: start address = 0x0, end address = 0x7ff
configuration memory

Programming/Verify complete

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 messages 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

Return to top


Depending on the position of POT1, the LEDs may be lit. As the POT1 is turned to the right or clockwise, more LEDs should be lit. As the POT1 is turned counterclockwise the LEDs should go out in order. The whole time the main.c while(1) loop continues to run without any action.

Final Project


Setting up an automatic ADC measurement can be extremely useful especially when there are actions that the main loop does need to perform. Especially when the main loop uses the ADC data. This example is simple but does show how to use a timer to control the ADC and then how the ADC can perform the measurements independently. This project can be expanded to control any I/O pin on the Curiosity Development Board pin instead of the LEDs. This can make this a useful base program for applications that need to control a digital device based on an analog input signal.

Return to top