1 ;;

     2 ;; Basic ADC operation

     3 ;;

     4 

     5 ; Reference select

     6 .set ADC_REF    = 0b01      ; AVcc

     7 

     8 ; Bit adjustment

     9 .set ADC_LAR    = 1         ; Left-adjust

    10 

    11 ; Input select

    12 .set ADC_MUX    = 0b000     ; ADC0

    13 

    14 ; Auto-trigger source

    15 .set ADC_ATS    = 0b011     ; TC0 OCA

    16 

    17 ; Auto-trigger enable

    18 .set ADC_ATE    = 1

    19 

    20 ; Prescaler

    21 .set ADC_PS     = 0b111     ; 1/128

    22 

    23 ; I/O pins

    24 .equ ADC_DDR    = DDRC

    25 .equ ADC_PORT   = PORTC

    26 .equ ADC_PIN    = PORTC0

    27         

    28 ;; Initialize the ADC for starting conversions

    29 ADC_Init:

    30     ; ADMUX

    31         ldi         r16, (ADC_REF << REFS0) | (ADC_LAR << ADLAR) | (ADC_MUX << MUX0)

    32         sts         ADMUX, r16

    33     

    34     ; ADCSRB

    35         ldi         r16, (ADC_ATS << ADTS0)

    36         sts         ADCSRB, r16

    37 

    38     ; ADCSRA

    39         ; ADSC: No need if using external auto-trigger ???

    40         ; Enable interrupt

    41         ldi         r16, (1 << ADEN) | (1 << ADSC) | (ADC_ATE << ADATE) | (1 << ADIE) | (ADC_PS << ADPS0)

    42         sts         ADCSRA, r16

    43     

    44     ; Disable digital circuit for pin

    45         ldi         r16, (1 << ADC_PIN)

    46         sts         DIDR0, r16

    47 

    48     ; Done

    49         ret

    50 

    51 ;; Interrupt handler stub for ADC_HANDLER

    52 ADC_Interrupt:

    53         in          r0, SREG

    54 

    55         rcall       ADC_HANDLER

    56 

    57         out         SREG, r0

    58         reti

    59 

    60 ;; Read the current 8-bit ADC sample 

    61 ; Returns value in r16

    62 ADC_Read8:

    63     ; Copy

    64         lds         r16, ADCH

    65 

    66     ; Done

    67         ret

    68