2024-04-19

On the arduino board, the LED is marked as pin number 13. However, in the microcontroller, the equivalent pin is number 19.

                 +-\/-+
           PC6  1|    |28  PC5 (AI 5)
     (D 0) PD0  2|    |27  PC4 (AI 4)
     (D 1) PD1  3|    |26  PC3 (AI 3)
     (D 2) PD2  4|    |25  PC2 (AI 2)
PWM+ (D 3) PD3  5|    |24  PC1 (AI 1)
     (D 4) PD4  6|    |23  PC0 (AI 0)
           VCC  7|    |22  GND
           GND  8|    |21  AREF
           PB6  9|    |20  AVCC
           PB7 10|    |19  PB5 (D 13)
PWM+ (D 5) PD5 11|    |18  PB4 (D 12)
PWM+ (D 6) PD6 12|    |17  PB3 (D 11) PWM
     (D 7) PD7 13|    |16  PB2 (D 10) PWM
     (D 8) PB0 14|    |15  PB1 (D 9) PWM
                 +----+

The below is how you'd set the pin 19 using asm.

For more detailed information about setting atmega328p pins see:

• io pins

For a refresher of AVR assembly language see:

• avr instructions

The example below is similar to the one in the I/O ports documentation in the ATMega328p datasheet.

ldi r16, (1<<PB5)
out _SFR_IO_ADDR (DDRB), r16

Note that:

• PB5 is a macro that evaluates to 5.
• 1<<5 = 0b10000.
• ldi only works for registers 16 to 31.
• out copies the value of r16 to an IO port or SFR.
• DDRB is a macro that evaluates to the address of DDRB.
• _SFR_IO_ADDR is a macro that conver the absolute address of DDRB to the relative address in the special function registers (SFRs). This is because out is optimised to only use relative addresses.