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Burnout Current Sources
12-7
Analog-to-Digital Converter
12.4 Burnout Current Sources
When the Burnout bit (BOD) is set in the ADC control register (ADCON0.6),
two current sources are enabled that source approximately 2µA.
This allows for the detection of an open circuit (full-scale reading) or short-cir-
cuit (0V differential reading) on the selected input differential pair.
The following program illustrates a simple open-circuit and short-circuit detec-
tion routine.
#include <REG1210.H>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define LSB 298.0232e−9
extern void autobaud(void);
extern long bipolar(void);
void main(void)
{
float sample, decimation = 1728;
CKCON = 0; // 0 MOVX cycle stretch
autobaud();
printf(”Brown−Out Detection\n”);
//Timer Setup
USEC= 10; // 11MHz Clock
ACLK = 9; // ACLK = 11,0592,000/10 = 1,105,920 Hz
// modclock = 1,105,920/64 = 17,280 Hz
// Setup ADC
PDCON &= 0x0f7; //turn on adc
ADMUX = 0x01;
ADCON0 = 0x70; // Vref On, Vref Hi, Buff off, BOD on, PGA=1
ADCON2 = decimation & 0xFF; // LSB of decimation
ADCON3 =(decimation>>8) & 0x07; // MSB of decimation
ADCON1 = 0x01; // bipolar, auto, self calibration, offset, gain
while(1)
{
while (!(AIE & 0x20));
sample = bipolar() * LSB; // This read clears ADCIRQ
printf (”Sample=%f”, sample);
if(sample < 0.01)
printf(” Short Circuit\n”);
else if(sample > 2.4)
printf(” Open Circuit\n”);
else
printf(“Normal Sensor Range\n”);
while(!RI);
RI = 0;
}// while
} //main