[Amforth-devel] A2D problems with ATmega128

[Bernard M. <bme...@gm...>]

Hi All,

I am having a problem getting the A2D subsytem working on the ATmega128. I
have used a modified version of the lcd.frt supplied, but in use I am
getting a number that is the same returned for all channels, and applying a
voltage to the A2D input has no effect (Port F pins).

If I change the scaler parameter for +adc, then I get different numbers, but
still not reading the inputs. Is there somethink else that connects the pins
to the A2D module, I can't see it in the manual, and the example code
doesn't show any extra setup to configure the pins.

I also note that in the "waitadc"  word, I had to wait for ADSR to go low,
not wait for ADIF to go high, as in the example code, otherwise that word
would just hang .. also don't know why the original code starts the a2d
convertor twice?

The code is below, so please have a look and let me know if I am doing
anything incorrect ..

Many Thanks,
Bernard.

PS: The other change I made to the original code "butterfly example" was to
remove references to the VCP pin.

-------------------------------------------------------- Code follows
--------------------------------------------------
\ ADC Routines
---------------------------------------------------------------------------------------------


marker _adc_

hex

\ Register defines
26 constant ADCSRA
25 constant ADCH
24 constant ADCL
27 constant ADMUX

ADCSRA 7 portpin: ADEN
ADCSRA 6 portpin: ADSC

\ Init the ADC sub system
: +adc ( scaler channel -- )
    ADMUX c!          ( -- scaler )
    log2  2 max   \ lowest 3 bits but at least 2
    1 7 lshift or \ msb
    ADCSRA c!
;

\ wait until the adc is finished
: waitadc ( -- )
    begin
        ADCSRA c@
    [ hex ] 40 and 0=
    until
;

\ fetch the value of the initialized adc channel
: adc@ ( -- adc )
    ADEN high         ( -- )
    ADSC high \ start converter
    waitadc         ( -- )
    0               ( -- 0 )
    8 0 do          ( -- n )
    ADSC high     ( -- n )
    waitadc     ( -- n )
    ADCL c@    ADCH c@ 8 lshift + ( -- n adc_i )
    +           ( -- n )
    loop            ( -- n )
    3 rshift        ( -- adc )
;