ADC reading and configuration problem

Hi everyone,

I can't get my ADCs to working properly. I've tried to play with the registers, with no results.

I have to sample 4 analog inputs.

Only one reading is correct, it's the "tsense" refered to the ADCIN5. The others values displayed are completely crazy.

I'm using the PIC18F4431 ( datasheet : http://ww1.microchip.com/downloads/e...Doc/39616d.pdf )

The simple code used for the test :

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

TRISA=%11111111
TRISB=%11000000 
TRISC=%110000   
TRISD=%11100     
TRISE=%11111111

ANSEL0=%11111111
ADCON0=%00011111
ADCHS=%01010101

potsense var word
tsense var word
usense var word
isense var word

pause 2000
LCDOUT $fe,1

lp:

ADCIN 4,potsense
ADCIN 5,tsense
ADCIN 6,usense
ADCIN 7,isense

lcdout $fe,$2,DEC5 potsense," ",DEC5 tsense
lcdout $fe,$c0,DEC5 usense," ",DEC5 isense

pause 10

goto lp

---

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

Quote:

---

Originally Posted by 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

---

Hi,

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

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.

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

Quote:

---

Originally Posted by mackrackit

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).