ADC Component change ref voltage

[Steve001]

Afternoon all

using a PIC16F18875 and I want to change the internal ref voltage to 1.024 volts

http://www.matrixtsl.com/wikiv7/index.p ... a0dd265bce

I am not 100% sure on how to change this, don't fully under stand the wiki

If someone could advise

Steve

[Benj]

Hi Steve,

Change the VRefOption to FVR.
Change the VRefVoltage to 102.

Then use the following C code to configure the FVR peripheral.

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FVRCON = 0x81;

Hopefully that should be all that is required.

[Steve001]

Cheers Ben

Will have a go later and get back to you

Steve

[Steve001]

Afternoon

trying to get analogue input working, reading not making any sense at all

Connected LM35CAZto port E0

http://uk.farnell.com/texas-instruments ... st=9494529

test program reading not stable what so ever 0.000031 - 1.015899 voltage on scope 256mv which is probably correct for temperature in room

not 100 % sure if I have analogue port settings correct

if someone can advise

Steve

:edit

the plot thickens

1) tried the example file from the wiki - "Reading a sample as a Voltage" changed target device to PIC16F18875 and 4 x 16 display - example didn't work read rubbish

2) exact same example and setup - target device ECIO40P - working correctly

changed back to test 1

measured voltage with scope on chip input pin - correct

changed analogue inputs to different pin - not working (AN32 - RE0)

so is the problem with my device setup or is there something else a miss ?

[medelec35]

Hi Steve,

test program reading not stable what so ever 0.000031 - 1.015899 voltage on scope 256mv which is probably correct for temperature in room

not 100 % sure if I have analogue port settings correct

To me that sounds like the port is floating so wrong pin is being read or there is a bug with ADC.
What chip pin number have you connected the analogue signal to?

Then use the following C code to configure the FVR peripheral.

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FVRCON = 0x81;

I would have thought since this is set within

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PIC_CAL_ADC.c

then adding C code code block with

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FVRCON = 0x81;

would not work?

Steve,
Have you read this thread?

In your case you will need to search for

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TYPE_34

instead of

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TYPE_26

Martin

[Steve001]

Hi Martin

I am using port E0 (pin8) - i have checked the pin voltage is correct with my scope

I was looking at that post this afternoon, wasn't too confident in looking into that or fiddling with the code.

I will sit down tomorrow and have a go through it when i have a clear head

Steve

:edit

I also checked by using the example file in the wiki AN0, AN1, AN32 using standard analogue port settings - readings meaning less

[medelec35]

Hi Steve,
This is a long shot.
Can you connect the voltage to be measured to Pin 2 (AN0) and see what the Display reads?

Martin

[Steve001]

Hi Martin,

I checked by using the example file in the wiki AN0, AN1, AN32 using standard analogue port settings - readings meaning less

Steve

[medelec35]

Hi Steve, I was suspecting registers not being assigned with correct values?
There is a way to find out.
You could read the registers then send value to LCD.
Would you know how to do that?

Martin

[Steve001]

Hi Martin
To be honest I don't have a clue
If you can help me out with that one please

Steve

[medelec35]

Sure,
I will put something together tomorrow for you.

Martin

[Steve001]

Thank you

Steve

[medelec35]

Hi Steve,
Don't know if the attached file will help?
It will display the register name and below will display the register value in binary which makes it easier to compare with the data sheet.

Martin

[Steve001]

Hi Martin

Connected my LM35 to E0 - measured 233.1mv on scope

cannot make end or tail of this

I let it run for 4 passes and got different results

Looking at the FVRCON Register 11000001

Fixed Voltage Reference is enabled
Fixed Voltage Reference output is ready for use
Temperature Indicator is disabled
VOUT = VDD - 2VT (Low Range)
Comparator FVR Buffer is off
ADC FVR Buffer Gain is 1x, (1.024V)

or have I read this the wrong way round ? and why is ADC different values

looking at page 267 on data sheet

http://www.farnell.com/datasheets/22452 ... 1501615565


Steve

[medelec35]

Hi Steve,
From your results it looks like ADCON0 is either not being assigned correctly or it's being cleared within PIC_CAL_ADC.c
On further investigation its the latter.
In order to view ADCON0 SFR:
Can you make a back up copy of PIC_CAL_ADC.c in

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C:\Program Files (x86)\Flowcode 7\CAL\PIC\PIC_CAL_ADC.c

if 64 bit windows
or

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C:\Program Files\Flowcode 7\CAL\PIC\PIC_CAL_ADC.c

if 32 bit windows.
Then replace original with attached version, which will be for diagnostics only.

Martin

[Steve001]

cheers martin will have a go tonight

do I reprogram device with new file and re run ?

Steve

[medelec35]

Hi Steve,

do I reprogram device with new file and re run ?

Yes or else there will be no difference in your results.
I'm interested in what the new ADCON0 results are.

Martin

[Steve001]

Doh ... had a blonde moment then sorry ...

[Steve001]

here you go martin

measured 233.1mv on scope

Steve

[medelec35]

Hi Steve,
I have noticed some confusion with the datasheet;
It shows on page 344:

ADC Conversion.png

(95.65 KiB) Downloaded 10822 times

Which shows to use ADCON0 for analogue channel selection.
Yet further down the datasheet it shows:

ADC Channel selection.png

(87.54 KiB) Downloaded 10822 times

Can you change one of the registers in the flowchart to

Code: Select all

ADPCH

and recompile.
Don't forget to refresh flowchart before compiling.
From the results, we could get further.

Martin

[Steve001]

Hi Martin

do you want me to use the original cal file or your modified one ?

I was reading that data sheet too last night but not as far down as that page, I did notice something that FVR is on port AN1 ???? I was getting confused at this point also too

I will have another go tonight

Steve

[medelec35]

Hi Steve,

do you want me to use the original cal file or your modified one ?

Nothing requires changing on cal file:

Can you change one of the registers in the flowchart to
CODE: SELECT ALL
ADPCH
and recompile.

There are two different ways.
1) Go in to a switch branch of flowchart.
Change a name of both C code and calculation box to desired register.
E.g change

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FCV_REGISTER_VALUE=ADCON1;

&

Code: Select all

RegisterName = "ADCON1"

to

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FCV_REGISTER_VALUE=ADPCH;

&

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RegisterName = "ADPCH"

Or
2) Add an additional Switch from the flowchart symbols and double click on it.
Change the default

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0

to

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Count

In

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Cases:

change

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1

to

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11

Copy any of the two icons e.g

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FCV_REGISTER_VALUE=ADCON1;

&

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RegisterName = "ADCON1"

Paste in the

Code: Select all

11

branch of the new switch icon.
Just change the the register names of both icons so you have:

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FCV_REGISTER_VALUE=ADPCH;

&

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RegisterName = "ADPCH"

for branch 11.
Finally cut the

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Count = 0

from branch 10 and paste in the new branch 11.

Recompile flowchart.

Martin

[Steve001]

cheers martin will have a go tonight all been well

Steve

[medelec35]

No problem.
One thing.
Can you make sure the ADC channel being used within flowchart and hardware is not An0.

Cheers

[Steve001]

Hi Martin

i get the following error when I compile now

Launching the compiler...
C:\Program Files (x86)\Flowcode 7\compilers\pic\bin\xc8.exe --chip=16F18875 "analougue test 2.01.c" --MSGDISABLE=359,1273,1388
Microchip MPLAB XC8 C Compiler (Free Mode) V1.41
Build date: Jan 24 2017
Part Support Version: 1.41
Copyright (C) 2017 Microchip Technology Inc.
License type: Node Configuration

analougue test 2.01.c: main()
1245: FCV_REGISTER_ADPCH;
^ (192) undefined identifier "FCV_REGISTER_ADPCH"
(908) exit status = 1
(908) exit status = 1

C:\Program Files (x86)\Flowcode 7\compilers\pic\bin\xc8.exe reported error code 1



FINISHED

have I done something stupid cannot see anything

input connected to E0 - pin 8 still (AN32)

Steve