Time for part 2! 

Last time, I gave you the homework of downloading and installing MPLAB and finding a Curiosity Nano DM164144 .  

Once you have done your homework, it is time for STEP 3, get that first project running.

Normally my advice would be to breakout Mplab Code Configurator and get the initialization code up and running, but I did not assign that for homework!  So we will go old school and code straight to the metal.  Fortunately, our first task is to blink an LED.

Step 1: Find the pin with the LED.

A quick check of the schematic finds this section on page 3.

This section reveals that the LED is attached to PORT A bit 2.  

With the knowledge of the LED location, we can get to work at blinking the LED.

The first step is to configure the LED pin as an output.  This is done by clearing bits in the TRIS register.  I will cheat and simply clear ALL the bits in this register.

Next we go into a loop and repeatedly set and clear the the PORT A bit 2.  
 

#include <xc.h>

void main(void) {
    TRISA = 0;
    while(1)
    {
        PORTA = 0;
        PORTA = 0x04;
    }
    return;
}

Let us put this together with MPLAB and get it into the device.

First we will make a new project:

Second, we will create our first source file by selecting New File and then follow the Microchip Embedded -> XC8 Compiler -> main.c

give your file a name (I chose main.c)

And you are ready to enter the program above.

And this is what it looks like typed into MPLAB.

But does it work?

Plug in your shiny demo board and press this button:

And Voila!, the LED is lit... but wait, my code should turn the LED ON and OFF... Why is my LED simply on?

To answer that question I will break out my trusty logic analyzer.  That is my Saleae Logic Pro 16.  This device can quickly measure the voltage on the pins and draw a picture of what is happening.

One nice feature of this device is it can show both a simple digital view of the voltage and an analog view.  So here are the two views at the same time.  Note the LED is on for 3.02µs (microseconds for all of you 7'th graders).  That is 0.00000302 seconds.  The LED is off for nearly 2µs.  That means the LED is blinking at 201.3kHz. (201 thousand times per second).  That might explain why I can't see it.  We need to add a big delay to our program and slow it down so humans can see it.

One way would be to make a big loop and just do nothing for a few thousand instructions.  Let us make a function that can do that.

Here is the new program.

#include <xc.h>

void go_slow(void)
{
    for(int x=0;x<10000;x++)
    {
        NOP();
    }
}

void main(void) {
    TRISA = 0;
    while(1)
    {
        PORTA = 0;
        go_slow();
        PORTA = 0x04;
        go_slow();
    }
    return;
}

Note the new function go_slow().  This simply executes a NOP (No Operation) 10,000 times.  I called this function after turning the LED OFF and again after turning the LED ON.  The LED is now blinking at a nice rate.  If we attach the saleae to it, we can measure the new blink.

Now is is going at 2.797 times per second.  By adjusting the loop from 10,000 to some other value, we could make the blink anything we want.

To help you make fast progress, please notice the complete project Step_3.zip attached to this post.

Next time we will be exploring the button on this circuit board.  For your homework, see if you can make your LED blink useful patterns like morse code.

Good Luck 

Step_3.zip