Microcontrollers: From Assembly Language to C Using the PIC24 Family – Chapter 8 Example 1

Well I’m going to run with the PIC24 for the time being and use the Microcontrollers – From Assembly Language to C Using the PIC24 Family book, but jumping to chapter 8 as the assembly language is not what I want at the moment. It’s learning about C and the PIC24. Anyway, as I’m using the Explorer 16 board, I’m going to share the differences in the sample code that should apply. This is the first installment for chapter 8.

My first observation is the author hasn’t identified the file names of the examples in his book and as his book doesn’t include the full text of the samples, it’s a bit of guess work to find them. So I’ll help you along your way. The first example on page 258 is called “ledflash_nomacros” and it’s in the chap8 folder.

One thing you need to do with all the examples when using the Explorer16 board is define the macro EXPLORER16_100P either in the include/pic24_all.h file or it must be added to the MPLAB project (Use Project->Build Options-> Project, click on the MPLAB C30 tab, and in Macro Definitions click ‘Add’, and add EXPLORER16_100P). Where it makes sense, I’m going to use the macro definition to keep the original code in tact while adding specific changes for the Explorer 16 board.

Note: the PIM I’m using is the PIC24FJ128GA010 100pin PIM (Microchip part number MA240011).

So here is the source for main() for this exercise. The rest of the file should remain the same.

void a_delay(void) {
    uint16 u16_i,u16_k;
    // change count values to alter delay
    for (u16_k=1800; --u16_k;) {
        for (u16_i = 1200 ; --u16_i ; );
    }
}

int main(void) {
    configClock();  //clock configuration
    /********** GPIO config **********/
    #if defined(EXPLORER16_100P)
    // For the explorer 16, we're not going to use the open drain as the LED is
    // wired from ground through a current limit resistor direct to pin 91 of
    // the PIC24FJ128GA010
    _TRISA6 = 0;  //Config RB15 as output
    _LATA6 = 0;  //RB15 initially low
    while (1) {  //infinite while loop
        a_delay();  //call delay function
        _LATA6 = !_LATA6;  //Toggle LED attached to RB15
    } // end while (1)
   #warning using Explorer16 code
    #else // not EXPLORER16_100P
    #ifdef _ODB15  //PIC24F CPU header files define this instead of ODCB15
    _ODB15 = 1;  //enable open drain
    #else
    _ODCB15 = 1;  //enable open drain
    #endif
    _TRISB15 = 0;  //Config RB15 as output
   _LATB15 = 0;  //RB15 initially low
    while (1) {  //infinite while loop
        a_delay();  //call delay function
        _LATB15 = !_LATB15;  //Toggle LED attached to RB15
    } // end while (1)
    #warning NOT using Explorer16 code
    #endif  //#if defined(EXPLORER16_100P)
}

When you open the project file (.mcp) for this exercise you will notice the linker script in the linker scripts section of the files explorer. You need to delete this one. No need to add another one as MPLAB will pick up the right one automatically if you have used the default install.

You will notice in this code segment I’ve added a couple of warning messages for the compiler to see what parts of the code it compiles. You can have them in or take them out. They are there just to make sure the compiler is doing what is expected.

Now if you try and use DEBUG as per the default project, you will see a number of failures and the program wont run. The first will be a pop up message:

• ICDWarn0046:  Because clock switching is enabled, MPLAB ICD 2 requires the user to cycle target power after a program operation.

And then a message in the output window:

• ICD0083: Debug:  Unable to enter debug mode.  Please double click this message for more information.

I chose to ignore and change to a RELEASE build to see it working. Do this by following these steps:

1. Change the DEBUG drop down to RELEASE
2. Select a programmer (Programmer – Select Programmer). I’m using the MPLAB ICD2 so the rest talks about what happens with the ICD2.
3. Rebuild all (Ctrl+F10)
4. When you get the BUILD SUCCEEDED message, program the device (Programmer – Program). You will get the ICDWarn0046 message, just click OK.
5. When you get the “MPLAB ICD 2 ready for next operation”, disconnect the ICD2 and watch your program run. The LED second from left will flash at about once per second.