Analog input on the dsPIC30F4011

The following example program demonstrates basic analog input on the dsPIC30F4011. Only one of the ADC module’s four converters is used (AD0) and only one channel at a time is read. The sampling time is controlled manually and is currently set to 1µs, which should be adequate for any source impedance below the recommended maximum value of 5kΩ. The total time per measurement (including the sampling and conversion) should be less than 2.5µs.

I haven’t tested this thoroughly yet, but I have successfully used it to control the duty cycle of an LED (i.e. its brightness) with a pot connected to AN0 (pin 2).

//
// This is a simple analog input example for the dsPIC30F4011
// It configures the lowest 8 PORTB pins as analog inputs, then reads
// the voltage on AN0 repeatedly. The input voltage determines
// the brightness of an LED on RD0 by varying its duty cycle
// in proportion to the analog input reading.
//
// Written by Ted Burke - last updated 5-12-2010
//

#include <libpic30.h>
#include <p30f4011.h>

_FOSC(CSW_FSCM_OFF &amp; FRC_PLL16); // Clock speed = 7.5MHz x 16, i.e. 30 MIPS
_FWDT(WDT_OFF); // Watchdog timer off

void configure_pins();
unsigned int read_analog_channel(int n);

int main()
{
	long int n;

	// Set up which pins are which
	configure_pins();

	while(1)
	{
		// Read the analog channel. The result is an
		// integer between 0 and 1023 inclusive.
		n = read_analog_channel(0);

		// LED on
		_LATD0 = 1;
		__delay32(30*n); // m us

		// LED off
		_LATD0 = 0;
		__delay32(30*(1023 - n)); // (1023-n) us
	}

	return 0;
}

void configure_pins()
{
	// Configure digital I/O
	LATD = 0;
	TRISD = 0b11111110;

	// Configure analog inputs
	TRISB = 0x01FF;      // Port B all inputs
	ADPCFG = 0xFF00;     // Lowest 8 PORTB pins are analog inputs
	ADCON1 = 0;          // Manually clear SAMP to end sampling, start conversion
	ADCON2 = 0;          // Voltage reference from AVDD and AVSS
	ADCON3 = 0x0005;     // Manual Sample, ADCS=5 -&gt; Tad = 3*Tcy = 0.1us
	ADCON1bits.ADON = 1; // Turn ADC ON
}

// This function reads a single sample from the specified
// analog input. It should take less than 2.5us if the chip
// is running at about 30 MIPS.
unsigned int read_analog_channel(int channel)
{
	ADCHS = channel;          // Select the requested channel
	ADCON1bits.SAMP = 1;      // start sampling
	__delay32(30);            // 1us delay @ 30 MIPS
	ADCON1bits.SAMP = 0;      // start Converting
	while (!ADCON1bits.DONE); // Should take 12 * Tad = 1.2us
	return ADCBUF0;
}

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