Problems with ADC on PORTC.6 and PORTC.7

[bradsprojects]

Hi everyone. I have been trying to figure this one out for a while now and searches on the forum have not provided an help unfortunately.

Basically I am using a PIC18F26K22 microcontroller and am using four of the ADC pins, namely:

PORTA.5 = ADC.4
PORTC.2 = ADC.14
PORTC.6 = ADC.18
PORTC.7 = ADC.19

Now there is no problem with reading from PORTA.5 and PORTC.2 however I have not been able to get a reading from PORTC.6 or PORTC.7

I have ensured that ADC is enabled, I have made sure that the respective TRIS bits have been set, I have made sure that the respective ANSELA and ANSELC bits have been set. I have also checked to see if I need to disable any of the other features of those port pins but it seems that everything that I have done should be correct.

Has anyone had any issues with using PORTC.6 and PORTC.7 as ADC pins before? Can anyone shed any light on this issue?

Thank you in advance.

-Brad

[Jerry Messina]

The ADC library hasn't been modified for all the channels that the K22 supports... it only allows for 16 channels.

Try this:

Code: Select all

// adc read for 26K22
public function Read(pChannel as byte) as word
   // set channel...
   ADCON0 = (ADCON0 and $03) or (pChannel << 2)	
   
   // read ADC...
   if FAcquisitionTime = 0 then
      Enabled = true  
      Convert = true
   else   
      Enabled = true  
      delayus(FAcquisitionTime)
      Convert = true  
   endif  
   
   // wait for completion, then disable ADC...
   while Convert      
   wend           
   Enabled = false   
   Result = ADResult
end function

[bradsprojects]

Thank you Jerry, that fixed it up.

I didn't even think at looking at the ADC library, perhaps if I did I would have spotted the problem!