CLC Controlled Train Crossing Display
Objective
The Core Independent Peripherals within the latest PIC® 8-bit microcontrollers offer the opportunity to perform hardware functions without the CPU core running any code. This can be extremely useful for applications that need to perform applications without interruption from the main application. This simple example shows how to set up and use several Configurable Logic Cell (CLC) to produce a train crossing light. Two LEDs are controlled by a pair of CLC modules and a timer peripheral. To add function, the momentary switch S1 toggles between the train crossing flashing and a single LED light in the center (D6 LED), light through a separate set of CLC modules, and a timer used to control the switch debounce. The main.c file contains no special application code, just a continuous while(1) loop.
Reference Materials
Curiosity Development Board User’s Guide
Connection Diagram
The Curiosity board has four LEDs prewired to the I/O pins shown below. This project controls three of the four LEDs.
| Hardware Function | Pin | Setting |
|---|---|---|
| IO_LED_D4 | RA5 (2) | Output |
| IO_LED_D5 | RA1 (18) | Output |
| IO_LED_D6 | RA2 (17) | Output |
| IO_LED_D7 | RC5 (5) | Output |
The Curiosity board also has a momentary switch labeled S1 and is connected to the RC4 pin of the PIC16F1619 microcontroller. The switch will be used to toggle the flashing on and off, similar to the way that an approaching train triggers a real train crossing signal.
Create a Project
Create a new project and select the PIC16F1619 along with the Curiosity Board and MPLAB® XC8 compiler.
Launch MCC
Open the MPLAB Code Configurator (MCC) under the Tools > Embedded menu of MPLAB X IDE.
System Setup
From Project Resources choose System Module to open the System Setup window within MCC.
- In the clock settings, make sure you select INTOSC
- Select the system clock FOSC.
- Set the Internal Clock field to the 4MHz_HF setting.
- The Curiosity 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.
Timer 2 Setup
Add the TMR2 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 TMR2 entry to add it to the Project Resources list. Then click on the TMR2 to open the configuration setup screen.
Timer 0 Setup
Add the TMR0 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 TMR0 entry to add it to the Project Resources list. Then click on the TMR0 to open the configuration setup screen.
Set Timer Period to: 32.768 ms.
CLC1-CLC4 Setup
Add the CLC1 - CLC4 peripherals to the project from the Device Resources area of MCC. To do that, scroll down to the CLC entry and expand the list by clicking on the arrow. Now double click-on the CLC1 through CLC4 one at a time to add them to the Project Resources list. Then click on the CLC to open the configuration setup screen.
CLC1
Make the changes shown to the CLC1 block diagram.
Change the Mode to JK Flip Flop with R.
CLC2
Make the changes shown to the CLC2 block diagram.
Change the Mode to 4-input AND.
CLC3
Make the changes shown to the CLC3 block diagram.
Change the Mode to 1-input D flip flop with S and R.
CLC4
Make the changes shown to the CLC4 block diagram.
Change the Mode to JK Flip Flop with R.
Pin Manager Setup
Click on RA2 lock in the CLC4OUT row to turn the lock green.
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.
main.c
Since the project runs completely independent of the core, the generated main.c doesn't need any modification. The default while(1) loop will be the only code running.
while (1)
{
// Add your application code
}
/**
End of File
*/ 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)
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... Programming/Verify complete
Results
The D4 and D7 LEDs will begin flashing back and forth like a train crossing. Press the S1 switch and that will stop and the D6 LED will light and stay lit until the S1 switch is pressed again. When it's pressed the second time the D6 LED will go out and the D4 and D7 will begin flashing back and forth again.
Conclusions
Setting up several CLCs along with the timers can take a little bit of time but the MCC makes generating the proper register setup for these Core Independent Peripherals as easy as clicking on the Generate button. Once the drivers are generated, programming the microcontroller is the only step left to have a train crossing application running on the Curiosity board. Additional code could be added later (typically to main.c) but it won't affect the operation of the train crossing as that will be running independently.