ADC reading and configuration problem

[mark_s]

Hello,

I had the same problem a while back. The adcin command does not work with the
pic18fxx31s. You have to read them manually. See this thread it may help.

http://www.picbasic.co.uk/forum/show...ght=PIC18F2331

[pxidr84]

Hello,

I had the same problem a while back. The adcin command does not work with the
pic18fxx31s. You have to read them manually. See this thread it may help.

http://www.picbasic.co.uk/forum/show...ght=PIC18F2331

Hi,

I've tried this (from Bruce's code) :

DEFINE OSC 32      
DEFINE LCD_DREG PORTC
DEFINE LCD_EREG PORTD
DEFINE LCD_RSREG PORTD
DEFINE LCD_EBIT 0
DEFINE LCD_RSBIT 1
DEFINE ADC_BITS 10
   
  CH1 VAR WORD
    CH2 VAR WORD
    CH3 VAR WORD
    CH4 VAR WORD
    
    ' Analog setup
    ' Single shot, multi-channel, simultaneous Mode2, Groups A+B, then C+D
    ADCON0 = %00011101
    
    ' Set +/- Vref to AVdd/AVss, FIFO buffer enabled
    ADCON1 = %00010000
    
    ADCON2 = %11001111   ' Right justified, 24 Tad, Frc
    ADCON3 = 0           ' Disable all triggers
    ADCHS = 0            ' Channel select for AN0,1,2,3
    ANSEL0 = %00001111   ' AN0,1,2,3 analog input, rest digital
 
Main:
    ADCON0.1 = 1         ' Start the conversion
    WHILE ADCON0.1=1     ' Wait for it to complete (all 4 channels)
    wend
    
    ' FIFO buffer holds all 4 channels. Reading ADRESH & ADRESL automatically
    ' increments the buffer pointer (on read of ADRESL) to the next channels
    ' storage location.
    CH1.HighByte = ADRESH ' get result from AN0
    CH1.LowByte = ADRESL  ' Increment buffer pointer
    
    CH2.HighByte = ADRESH ' get result from AN1
    CH2.LowByte = ADRESL  ' Increment buffer pointer
    
    CH3.HighByte = ADRESH ' get result fron AN2
    CH3.LowByte = ADRESL  ' Increment buffer pointer
    
    CH4.HighByte = ADRESH ' get result from AN3
    CH4.LowByte = ADRESL  ' clears buffer pointer
  
   
    ' show 4 A/D channel results
    lcdout $fe,$2,DEC5 CH1," ",dec5 CH2
    lcdout $fe,$c0,DEC5 CH3," ",dec5 CH4
   
    pause 100
 
    GOTO Main

The readings works, but the lower bits of the reading are unstable, and I don't know why.

[mackrackit]

What is the source of the analog? Do you have smoothing capacitors from the ADC pins to VSS? Sometimes that helps.

[pxidr84]

What is the source of the analog? Do you have smoothing capacitors from the ADC pins to VSS? Sometimes that helps.

In fact I've resolved my problem. The result of the ADC was configured to be right-justified (ADCON2.7=1), I've set it to be left-justified (ADCON2.7=0), and I haven't problems anymore (the readings are perfectly stable now).