AVR Pascal (AVRCo) ADC Interrupt

Despite AVRCo offering the ADC as library function, without the source it sooner or later leads to problems, eg when internal averaging is considered, and is therefore to be avoided. Here, a replacement with source is provided. Contrary to the provided library ADC, some more decision have to be made.

the main

In the main, the ADC is handled when the flag ADCDone appears.

VAR 
 ADCDone:bit;
 ADCChannel:byte;
 ADCLoop:byte;
 CurrentADC:word;
 CurrentADClo[@CurrentADC]:byte;
 CurrentADChi[@CurrentADC+1]:byte;
 ADCBuf:Array[0..7]of word;       //averaging location
 ADC:Array[0..7]of word;          //user location

begin
 ..
 SetupADC;
 ..
 EnableInts;
 ..
loop
  ..
  if (ADCDone=1) then
   .. do whatever here
   ADCDone:=0;         // clear flag
  endif;
  ..
endloop;
end; // main

The ADC interrupt

The ADC is generally handled with a statemachine what the channel and averaging concerns. Here, all 8 channels were sampled and averaged with an "exponential 16" algorithm. The statemachine allows to filter different channels with different filters.

interrupt ADCRdy; // read ADCL before ADCH
begin
 CurrentADClo:=ADCL;                                 //temp var
 CurrentADCHi:=ADCH;
 ADCBuf[ADCChannel]:=ADCBuf[ADCChannel]+CurrentADC;
 if (ADCLoop=15) then  // 2^N -1
  ADC[ADCChannel]:=ADCBuf[ADCChannel] shr 4;
  ADCBuf[ADCChannel]:=0;
  if (ADCChannel=7) then
   ADCChannel:=0;
   ADCLoop:=0;
   ADCDone:=true;
  else inc(ADCChannel);
  endif;
 else
  inc(ADCChannel);
  if (ADCChannel=8) then
   inc(ADCLoop);
   ADCChannel:=0;
  endif;
 endif;
 ADMUX:=(ADCChannel and $07)or $40;
 ADCSRA:=$CF; // enable, start, no free run, div 128, interrupts
end;

Setup the ADC

The setup involves setting the channel, and the speed. Plus here the involved variables are also set.

procedure SetupADC;
begin
 ADMUX:=$40; // AVCC, channel:=0;
 ADCSRA:=$CF; // enable, start, no free run, div128, interrupts, 480us/sample
 ADCLoop:=0;
 ADCChannel:=0;
end;

Questions ?
Suggestions?
Feedback ?

sponsored links

embedded
home

last updated : 10.may.04, or perhaps later

Copyright (99,2004) Ing.Büro R.Tschaggelar