How to store in ACSR and ADCSRA/B (AVR)

Question

I've been trying to make a comparator in AVR using Proteus 8 with an Arduino ATMega 328P. I've been told that the comparison is practically made by the Arduino, so I just need to get the value from the location, but I haven't been able to access it. I've tried with LDI, SBI and IN/OUT instructions, but haven't worked.

Here's the code I've right now

    ;When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin AIN1, the Analog Comparator output, ACO, is set.

;------Preps--------
LDI R16,0xFF    ;16 inFF
LDI R17,0x00    ;17 in00
LDI R18,0x80
LDI R19,0x40
LDI R21,0x20
OUT DDRC,R16    ;C out
;CBR ACSR,0x40  ;Clean the 6th ACSR bit to get the AIN0 input
STS ADCSRA,R18  ;Set the 7th ADCSRA bit (ADEN) to get AIN1 input
STS ADCSRB,R19  ;Set the 6th ADCSRB bit (ACME) to get AIN1 input
;CBR ACSR,0x0D   ;Clean 0,1 and 3 in ACSR to obtain toggle with ACO and disable the interruption
OUT ACSR,R21    ;Clean ACSR register


;----------------------------------------------------*

;----------------------------------------------------*
loop:
    NOP
    NOP
    IN  R20, ACSR       
    CPI R20,0x80  ;Compare registers r1 and r0
    BREQ aco1      ;If equal
    RJMP aco0      ;IFNE aco0 
    
aco1:
    OUT PORTC,R16 ;Turns on the led
    RJMP loop     ;Goes back to verify if ACO changed

aco0:
    OUT PORTC,R17 ;Turns off the led
    RJMP loop     ;Goes back to verify is ACO changed

I can't configure the inputs because I can't store at ADCSRA/B