I have an ATmega328P Arduino and am trying to make the LED blink using assembly without any additional includes. The goal is to have it blink for 1 second on, then 1 second off, however, it blinks incredibly quickly and is barely perceptible. Am I doing something incorrectly?
; DDRB (Data direction register for the pin with LED) = 0x04
; PORTB (pin with LED) = 0x05
; TCCROB = 0x25
; TCNT0 = 0x26
; 0b00000000 = OFF
; 0b00100000 = ON
setup:
ldi r16, 0b00100000 ; Set r16 to LED ON value
out 0x04, r16 ; Set DDRB to output
out 0x05, r16 ; Set PORTB to ON
ldi r16, 0b00000101 ; Set r16 with prescaler 1024 value
out 0x25, r16 ; Set the TCCROB to 1024
ldi r20, 0 ; Reset r20
loop:
in r17, 0x26 ; Read the timer
cpi r17, 128 ; Check to see if the timer is halfway done (1/2 second, max 255 value)
brbc 0, increment ; If r17 <= 128 (max 255 val before resets to 0), invert current LED state
;rjmp loop
increment:
adc r20, 1 ; Add 1 to r20 (with carry)
brbs 0, reset ; If the carry branch is set, reset the register
rjmp loop ; Otherwise, run the clock
reset:
ldi r20, 0 ; Reset the delay register
cpi r16, 0b00000000 ; Check if r16 is set to LED OFF
brbs 1, switchon ; If it is, change it to ON
ldi r16, 0b00000000 ; Otherwise, change it to OFF
out 0x05, r16 ; Set the LED to the new state
rjmp loop ; Run the clock
switchon:
ldi r16, 0b00100000 ; Set r16 to LED ON value
out 0x05, r16 ; Set the LED to the new state
rjmp loop ; Run the clock
