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dmitrboristuk
Joined: 26 Sep 2020
Posts: 55
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| FVR setup_vref() does not work |
 Posted: Fri Mar 05, 2021 1:40 pm |
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Hello!
PIC16F1705 does not work the function of setting the reference voltage for the ADC. I tried as a source of reference voltage VDD or Vref, with them the ADC works great. But I need an VRF. How do I fix this problem?
Version 5.093 |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Mar 05, 2021 2:36 pm |
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| Post the lines of code that you're using to setup the ADC. |
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dmitrboristuk
Joined: 26 Sep 2020
Posts: 55
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| Posted: Fri Mar 05, 2021 2:48 pm |
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| Code: |
setup_vref ( VREF_ON | VREF_ADC_4v096 |
VREF_COMP_DAC_2v048 |
TEMPERATURE_INDICATOR_DISABLED );
SETUP_ADC_PORTS( sAN6 ) // ะก2
setup_adc_reference(VSS_VREF);
setup_adc(ADC_CLOCK_INTERNAL);
set_adc_channel( 6 ); |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19515
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| Posted: Fri Mar 05, 2021 10:27 pm |
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Look again at the .h file.
The FVR is called FVR, not VREF. You are currently setting up the ADC to
use the external VREF, not the FVR..... |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Mar 06, 2021 12:01 am |
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Here is a test program that demonstrates what Ttelmah is saying.
I was testing this in hardware and it works.
| Code: | #include <16F1705.h>
#device ADC=10
#use delay(internal=4M)
#pin_select TX1=PIN_C4
#pin_select RX1=PIN_C5
#use rs232(UART1, baud=9600, ERRORS)
//===================================
void main()
{
int16 adc_result;
setup_vref ( VREF_ON | VREF_ADC_4v096 |
VREF_COMP_DAC_OFF |
TEMPERATURE_INDICATOR_DISABLED );
setup_adc_ports(sAN6);
setup_adc_reference(VSS_FVR);
setup_adc(ADC_CLOCK_DIV_4);
set_adc_channel(6); // PIN_C2
delay_us(5);
while(TRUE)
{
adc_result = read_adc();
printf("%lu \n\r", adc_result);
delay_ms(1000);
}
} |
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dmitrboristuk
Joined: 26 Sep 2020
Posts: 55
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| Posted: Sat Mar 06, 2021 12:06 am |
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This function does not turn on the FVR for any value of the argument. Moreover, the voltage from the FVR does not come to the comparator either.
You can somehow enable FVR using assembler commands |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Mar 06, 2021 2:14 am |
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| dmitrboristuk wrote: |
This function does not turn on the FVR for any value of the argument. |
What do you mean by "this function" ? Do you mean this one:
| Code: | | setup_adc_reference(VSS_FVR); |
The line above produces this .LST file:
| Quote: | ....... setup_adc_reference(VSS_FVR);
00AC: MOVLB 01
00AD: BSF 1E.0 // ADCON1.0 = 1
00AE: BSF 1E.1 // ADCON1.1 = 1
00AF: BCF 1E.2 // ADCON1.2 = 0
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The 16F1705 data sheet shows this is the correct setting to use the FVR:
| Quote: |
1-0 ADPREF<1:0>: ADC Positive Voltage Reference Configuration bits
11 = VREF+ is connected to internal FVR_buffer1(1)
10 = VREF+ is connected to external VREF+ pin(1)
01 = Reserved
00 = VREF+ is connected to VDD |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19515
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| Posted: Sat Mar 06, 2021 2:31 am |
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Yes, it does.
It does not go to the comparator, VREF_COMP_DAC_OFF says to not send
it there.
However as posted, I've checked the listing, and this:
setup_adc_reference(VSS_FVR);
turns on the Vref set to *4, and sends this to the ADC.
As PCM also says, the ADC setup selects this.
You do realise that the Vref output cannot be above the supply, and in fact
needs about 0.6v headroom in the supply voltage to work.
I checked with your compiler version. |
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temtronic
Joined: 01 Jul 2010
Posts: 9226
Location: Greensville,Ontario
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| Posted: Sat Mar 06, 2021 6:30 am |
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As Mr. T points out there are 'specs' for it !
What we don't know is what voltage you're running the PIC on ?
That PIC is good for both 3 and 5 v operation but....
you can't have it run at 3 volt and expect the ADC to read 5 volts !
Jay |
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dmitrboristuk
Joined: 26 Sep 2020
Posts: 55
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| Posted: Sun Mar 07, 2021 1:29 pm |
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| Is it possible to somehow disrupt the operation mode of the FVR by incorrectly setting the fuse bits? |
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temtronic
Joined: 01 Jul 2010
Posts: 9226
Location: Greensville,Ontario
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| Posted: Sun Mar 07, 2021 4:28 pm |
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I don't see how a 'fuse' could affect the FVR but.......
hmm, it'd be a good idea to post your current, complete program. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19515
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| Posted: Mon Mar 08, 2021 2:24 am |
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Agreed on seeing some demo code.
Though there are no fuses that affect the FVR, there are things that
could make it look as if it was not working. For example your original
ADC clock (INTERNAL) will make the ADC results inaccurate. Then things
like not allowing sufficient Tacq between selecting a channel and reading,
could also lead to erratic results.
The compiler generated code does correctly enable the FVR on this chip.
You need to give us a chance to see what 'else' is wrong. |
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