A/D 16F916 Internal 4 Mhz Oscillator

[williamspv]

My problem is that I continually get either 0 0r 0x3ff in the ADRESH and ADRESL as the result of the A/D reading.

I am looking at table 12-1 of the spec and it shows an A/D RC clock source. Am I required to use this source since I am using an internal oscillator?

Code:

#include <16F916.h>
#device adc=8

#FUSES NOWDT //No Watch Dog Timer
#FUSES INTRC_IO //Internal RC Osc, no CLKOUT
#FUSES NOPUT //No Power Up Timer
#FUSES NOPROTECT //Code not protected from reading
#FUSES MCLR //Master Clear pin enabled
#FUSES NOCPD //No EE protection
#FUSES BROWNOUT //Reset when brownout detected
#FUSES IESO //Internal External Switch Over mode enabled
#FUSES FCMEN //Fail-safe clock monitor enabled
#FUSES DEBUG //Debug mode for use with ICD

#use delay(clock=4000000)
unsigned int16 value = 0;

void main()
{

setup_adc_ports(sAN0|sAN1|VSS_VDD);
setup_adc(ADC_CLOCK_DIV_8);
setup_spi(FALSE);
setup_lcd(LCD_DISABLED);
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_comparator(NC_NC_NC_NC);
setup_vref(VREF_LOW|-2);
setup_oscillator(OSC_4MHZ);
set_adc_channel(0);
delay_us(20);

while(1)
{
value = Read_ADC();
delay_ms(500);
}
}

Thanks for any help you can provide,

Patrick

[Ttelmah]

Setup_vref, only works on chips that have a programmable reference. I don't think the 819, does....

Best Wishes

[Guest]

[williamspv]

Even with the other setup code commented I still get the same results either 0 or 0x3ff for voltages varying from 3 - 5 volts at the pin.

Patrick

[PCM programmer]

He's actually using the 16F916, but there is a problem with the
setup_vref() statement.
You have got this statement:

[williamspv]

Thank you for your help. VREF shouldn't have an effect on my A/D reading because I have VSS_VDD selected, right?

If I have ADC=8 I get 255. I I have ADC=10 I get 1023 or 0x3ff. Why does the A/D return only the lowest value(0) or the highest value(255 or 1023)? I have added a set_tris_a command as another user did in a different thread, but I am still getting this result.

I also forgot to mention that I am using the compiler version 3.242.

Revised Code:
#include <16F916.h>
#device adc=10

#FUSES NOWDT //No Watch Dog Timer
#FUSES INTRC_IO //Internal RC Osc, no CLKOUT
#FUSES NOPUT //No Power Up Timer
#FUSES NOPROTECT //Code not protected from reading
#FUSES MCLR //Master Clear pin enabled
#FUSES NOCPD //No EE protection
#FUSES BROWNOUT //Reset when brownout detected
#FUSES IESO //Internal External Switch Over mode enabled
#FUSES FCMEN //Fail-safe clock monitor enabled
#FUSES DEBUG //Debug mode for use with ICD

#use delay(clock=4000000)

unsigned int16 value = 0;

void main()
{
set_tris_a(0b00000011);
setup_adc_ports(sAN0|sAN1|VSS_VDD);
setup_adc(ADC_CLOCK_DIV_8);

// setup_spi(FALSE);
// setup_lcd(LCD_DISABLED);
// setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
// setup_timer_1(T1_DISABLED);
// setup_timer_2(T2_DISABLED,0,1);
// setup_comparator(NC_NC_NC_NC);
// setup_vref(VREF_LOW|-2);
// setup_oscillator(OSC_4MHZ);
set_adc_channel(1);

while(1)
{
value = Read_ADC();
delay_ms(500);
}
}

Patrick