⚡ START HERE · THE ONLY LESSON YOU NEED

It's not magic.
Arduino is just a wardrobe with drawers and switches.

Inside the microcontroller there are 256 drawers (registers). Each one has 8 switches (bits).Switch #5 in drawer #5 turns on the LED onboard. That's it.

🗄️ ATmega328P — I/O REGISTERS (addresses 0x00 - 0x0F) First 16 drawers

0x00 (0x20) res

0x01 (0x21) res

0x02 (0x22) res

0x03 (0x23) PINB

0x04 (0x24) DDRB

0x05 (0x25)PORTB7
6
5
4
3
2
1
0

0x06 (0x26) PINC

0x07 (0x27) DDRC

0x08 (0x28) PORTC

0x09 (0x29) PIND

0x0A (0x2A) DDRD

0x0B (0x2B) PORTD

0x0C (0x2C) res

0x0D (0x2D) res

0x0E (0x2E) res

0x0F (0x2F) res

There are 256 drawers. Here only the first 16. Our drawer 0x05 (PORTB) is highlighted. Memory addresses (0x20-0x2F) in parentheses.

Inside this drawer there are 8 switches. Switch number 5 is connected to the LED on the board.

‑

D13 · LED

‑

LED on board (D13):

Off

sbi 5,5   ; turn on switch 5 of drawer 5 → LED ON
cbi 5,5   ; turn off switch 5 of drawer 5 → LED OFF
        

📌 This is not magic. It's just opening and closing a switch.

⚡ You understood the atom of Arduino.

Most people use pinMode and digitalWrite without knowing they're just opening and closing a switch in a drawer.

Now you know that:

0x05 is the drawer number (PORTB register)
Bit 5 is the switch that controls the LED onboard
sbi 5,5 closes the switch and the LED onboard turns on
cbi 5,5 opens it and the LED onboard turns off

This is the whole truth. Everything else is just different ways to say the same thing.

⚡ Try it now with a real Arduino

2 euro. One USB cable. Go to costycnc.it/avr1, write sbi 5,5, compile, upload. The LED turns on. Then cbi 5,5 and it turns off. You just modified the chip's "DNA".

It's not magic.Arduino is just a wardrobe with drawers and switches.

It's not magic.
Arduino is just a wardrobe with drawers and switches.