Nuts and Volts - February 2011

let’s be realistic. We are programming a microcontroller that does not have a computer screen associated with it, so we are limited initially with the Experimenter digital I/O. Fortunately, some of the I/O is connected to its onboard LEDs. In other parts of this series, we will show the use of USB to write to the computer screen, but for now we will use LEDs. To make our “Hello World” meaningful, we will start with the onboard LEDs and then advance to a 5x7 LED matrix for more exciting light shows that demonstrate the use of the RTOS and the PIC32 DMA controller. Here’s the run-down:

FIGURE 8.

Blinky code.

• Demo 1: Blinky LEDs — alternate blinking onboard LEDS ( BLINKY.MCP source).

• Demo 2: Turn on the LED with a pushbutton ( PUSHBTN.MCP source).

• Demo 3: RTOS individual LED control ( RTOS.MCP source).

• Demo 4: DMA transfer to LED ( DMA.MCP source).

continuous loop using a toggle function and a software delay for blink.

Demo 2 “Hello World” — Pushbutton LED

The particular 5x7 matrix for Demos 3 and 4 is shown in Figure 6, along with the hook-up diagram in Figure 7. Let’s start working through the different experiments.

Demo 1 “Hello World” — Blinky LEDs

This demo is similar in structure to Demo 1, but responds to either of the two Experimenter pushbuttons being depressed by lighting the corresponding LED associated with the button. This code is shown in Figure 9. The project is located in the PUSHBUTTON folder.

Demo 3 “Hello World” — Using an RTOS

The first demo is found in the Blinky folder, so open that folder and double-click on BLINKY.MCP. This should invoke MPLAB and bring up the Blinky project. Select your programmer/debugger, compile the project, and download the code to the Experimenter with your programmer/debugger hooked to ICSP. You should see the two LEDs on the Experimenter blink alternately.

Let’s examine the code. All these programs use #include <plib.h> to reference the PIC32 library and part. We then set the fuses for 80 MHz operation and the peripheral bus to 40 MHz.

Then, we invoke a library function “SystemConfig()”to optimize PIC32 operation. This function sets pre-fetch cache, RAM, and Flash wait states for the 80 MHz clock. Finally, we configure the digital I/O for LEDs and enter a An RTOS for microcontrollers is similar to operating