For example, on the ESP32 board there are several contacts that can issue pulses when the controller starts, which is connected with the operation of the chip itself. It is not recommended to connect devices that respond to input signals from the ESP to these contacts.

Tell me, are there any contacts on the Arduino UNO (Atmega328P) that give out any impulses at startup?

In particular, it is important for me to know about the following contacts:

  1. PB1 (9 pin)
  2. PD4 (4 pin)
  3. PD5 (5 pin)

enter image description here

Thank you!

  • 2
    on ATmegas the pins are INPUT at startup
    – Juraj
    Nov 6, 2019 at 15:33
  • 1
    If the arduino is programmed with a sketch, it depends on the sketch if the pin are input or output. If it is a new arduino the bootloader does not setup any outputs. An ESP has mostly a firmware installed. So the flashing pins are probably driven by this firmware. An Arduino may have a program already installed, that could also flash pins. Nov 6, 2019 at 15:41

1 Answer 1


Most Arduino boards come with a bootloader of some form. This bootloader may do things with IO pins. However apart from that, no, nothing else happens to any IO pins.

The bootloader may:

  • Flash pin 13 (built in LED)
  • Configure and communicate on pins 0/1 (UART)

With no bootloader then absolutely nothing happens on any IO pins.

  • thank you for the answer!
    – Delta
    Nov 6, 2019 at 15:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.