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16F676 vs 16F684

 
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arunkish



Joined: 23 Dec 2008
Posts: 83

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16F676 vs 16F684
PostPosted: Tue Jan 04, 2011 6:32 am     Reply with quote
Hi
Wish you all a happy new year. I have been reading ADC with 16F676 without any problem. I migrated to new controller 16F684 and used the same code to read the ADC. I am getting a value that is nearly 200 times higher than what I get in 16F676. setting #deivce adc=8 did not help. Is there anything that I should do more to make it work with 16F684.

Thanks & Regards
arunkish



Joined: 23 Dec 2008
Posts: 83

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PostPosted: Tue Jan 04, 2011 6:44 am     Reply with quote
Sorry forgot to tell how I had setup things..

in main:

Code:
setup_adc_ports(sAN0);



void readadc(void)
{
    int value;
   setup_adc(ADC_CLOCK_INTERNAL);
   set_adc_channel(0);
   delay_ms(5);
                value=read_adc();
}
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Tue Jan 04, 2011 1:08 pm     Reply with quote
Quote:
void readadc(void)
{
int value;
setup_adc(ADC_CLOCK_INTERNAL);
set_adc_channel(0);
delay_ms(5);
value=read_adc();
}

The internal ADC clock is not recommended for normal use by the
16F684 data sheet. Look in the following section of the data sheet:
Quote:

9.1.4 CONVERSION CLOCK

TABLE 9-1: ADC CLOCK PERIOD (TAD) VS. DEVICE OPERATING FREQUENCIES (VDD > 3.0V)

It shows the recommended ADC clock divisor to use for each PIC
oscillator frequency. For example, if you have a 4 MHz crystal, then
use Fosc/8. The CCS constant for this is ADC_CLOCK_DIV_8.
For 8 MHz oscillator, use ADC_CLOCK_DIV_16, etc. Look in the table
in the data sheet.

If that doesn't solve your problem, then post a small compilable test
program and post your compiler version.

Also post a description of the external circuit which is connected to the
A/D input of your PIC.
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