Pins 9 and 10 are hardware-linked to Timer 1 , a 16-bit timer that provides higher resolution for PWM compared to other pins. 🛠️ Hardware Specifications Pin Number Primary Function Special Feature Linked Hardware 9 Digital I/O 10 Digital I/O 8-bit PWM / SPI (SS) 11 Digital I/O 8-bit PWM / SPI (MOSI) ⚠️ Important Usage Notes
These pins are critical for SPI communication, which is used to talk to SD card readers, RFID modules, and high-speed displays: Pin 10: SS (Slave Select) Pin 11: MOSI (Master Out Slave In) Pin No 9 10 11
Using certain libraries (like the Servo library) can disable PWM functionality on pins 9 and 10 because the library "takes over" the internal Timer 1. Pins 9 and 10 are hardware-linked to Timer
In many standard LiquidCrystal setups, pins 11 and 10 are the default choices for the Enable (E) and Register Select (RS) connections. MISO (Master In Slave Out) — often paired
MISO (Master In Slave Out) — often paired with 10 and 11
All three pins are capable of PWM output (Arduino Reference). This allows you to simulate analog results (like dimming an LED or controlling motor speed) using digital signals.
On an Arduino Uno, pins 9, 10, and 11 are part of a specific group of pins with dual-purpose functionality: