Nuts and Volts - June 2010

THE DESIGN CYCLE

■ SCHEMATIC 1. The PIC24F/PIC32MX USB Trainer is a base

16-bit design with USB capability. The idea is for you to flesh out the basic design with your own personal set of peripherals. Allowing the user to add to the base design keeps the USB Trainer’s cost down and the usability high.

#ifndef EDTP_PIC24F_PIC32MX_TRAINER
#define EDTP_PIC24F_PIC32MX_TRAINER

Following our grand announcement of the hardware behind this code, you’ll encounter the bootloader options. You’ll find the bootloader code unchanged in our version of the HardwareProfile definitions. However, to inform the rest of the USB stack modules of our hardware’s presence we must declare ourselves one more time as to who we are:

#define EDTP_PIC24F_PIC32MX_TRAINER
#define CLOCK_FREQ 32000000

As you can see, it’s also a good time to tell the rest of the USB stack the speed of our CPU clock.

The LEDs included in the Trainer design serve a dual purpose. The status of the USB link enumeration is displayed in the LEDs. Once the link is up and running in the CONFIGURED state, the LEDs become part of the demo application which is part of the main.c file we’ll look at later. In keeping with Fred Eady’s First Law of Embedded Computing that “Nothing is free,” to utilize the LEDs we must configure them in the USB stack’s USB TRAINER.h file:

/** LED ****************************************/
#define mInitAllLEDs() LATC &= 0x9FFF; TRISC
 &= 0x9FFF;  //RC13, RC14

#define mLED_1
#define mLED_2

LATCbits.LATC13
LATCbits.LATC14

#define mGetLED_1()
#define mGetLED_2()

mLED_1
mLED_2

#define mLED_1_On()
#define mLED_2_On()

mLED_1 = 1;
mLED_2 = 1;

#define mLED_1_Off()
#define mLED_2_Off()

mLED_1 = 0;
mLED_2 = 0;

#define mLED_1_Toggle() mLED_1 = !mLED_1;
#define mLED_2_Toggle() mLED_2 = !mLED_2;

I chose to keep the USB stack’s original LED definition names. That makes it easier to get a successful compile as you don’t have to sift through the stack renaming the LEDs. As you’ll see later, the main.c application and status routines will utilize the LED GetLED, On, Off, and Toggle macros.