Nuts and Volts - June 2010

THE DESIGN CYCLE

POWERED_STATE)
{
mLED_Only_1_On();

}
else if(USBDeviceState ==
DEFAULT_STATE)
{
mLED_Only_2_On();

}
else if(USBDeviceState ==
ADDRESS_STATE)
{
if(led_count == 0)
{
 mLED_1_Toggle();
 mLED_2_Off();
}//end if
}
else if(USBDeviceState ==
CONFIGURED_STATE)
{
if(led_count==0)
{
mLED_1_Toggle();
if(mGetLED_1())
{
mLED_2_Off();

}
else
{
mLED_2_On();

 }
}//end if
}

It’s nice to be able to look at the LEDs and determine all of the other enumeration states. However, what you really want to see is LED1 and LED2 alternately blinking on your USB Trainer.

found in the usb_descriptors.c file.

I shorted the PIC24FJ256GB106’s AN0 ADC input to ground before issuing the 0x37 command. As you can see in the Read area of Screenshot 3, the ADC returned the command value followed by the ADC value of 0x0000. Screenshot 4 returned the 10-bit value of 0x3FF as I applied + 3. 3 volts to the ADC input before issuing the command to take a reading from the potentiometer’s wiper. The code used to read the potentiometer is relatively simple and is provided for us in the main.c demo application:

WORD_VAL ReadPOT(void)
{
WORD_VAL w;

#if defined(EDTP_PIC24F_PIC32MX_TRAINER)
  AD1CHS = 0x0; //MUXA uses AN0

 // Get an ADC sample
 AD1CON1bits.SAMP = 1;  //Start sampling
 for(w.Val=0;w.Val<1000;w.Val++);
//Sample delay, conversion start automatically
 AD1CON1bits.SAMP = 0;  //Start sampling
 for(w.Val=0;w.Val<1000;w.Val++);
//Sample delay, conversion start automatically
 while(!AD1CON1bits.DONE);  //Wait for
 //conversion
 //to complete

#else
 #error
#endif
w.Val = ADC1BUF0;

 return w;
}//end ReadPOT

MAGIC SMOKE STATION TEST

Since I’m writing this paragraph, you and I can get up on our donkeys and proclaim success! I’ve applied power via the USB portal and programmed the PIC24FJ256GB106. If you were here in the shop with me, you would see LED1 and LED2 going to town in an alternating manner and the POWER LED operating without a struggle.

Remember that analog input I mentioned earlier? Well, I can’t show you blinking LEDs but since we included the pot macros, I can show you data acquired from the PIC24FJ256GB106’s ADC. I’ll use the Kadtronix UsbHidDemo application to send the command and receive the data.

Screenshot 2 confirms that our PIC24F/PIC32MX USB Trainer has been recognized as a HID device by the UsbHidDemo application (which is running on my laptop). The EDTP Device Name was gleaned from the modification we made to the product string descriptor in the usb_descriptors.c file. The VID (1240) and PID (63) belong to Microchip and can also be Note that branding comes in handy once again as the ADC commands are particular to the PIC24F/PIC32MX USB Trainer. The ReadPOT function defines the analog port to read and, in this case, it is AN0. The ReadPOT