I am learning Arduino and one question asked what Arduino NANO's assignment of ATMEL's PD1* pin is. What does the asterisk mean in this context?

Edited to add NANO

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    \$\begingroup\$ Give some context. Where did you see the PD1*? The ATMEL's datasheet? In the Arduino pintout? In some webpage? It can that the pin has some footnote... We need more information. \$\endgroup\$ Commented Jul 15, 2020 at 8:41
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    \$\begingroup\$ Are you sure that the * isn't referring to a footnote somewhere on the same page? \$\endgroup\$ Commented Jul 15, 2020 at 8:42
  • \$\begingroup\$ @LaboratorioGluon I double-checked the question sheet and there were no footnotes to go with the asterisk. Plus, there are two questions where the pins are marked with an asterisk so i doubt it actually refers to a footnote \$\endgroup\$
    – user208872
    Commented Jul 15, 2020 at 9:21
  • \$\begingroup\$ "question sheet"? Are you doing your homework and expecting us to know what is written on your papers somewhere or what it means in a context of your assignment? \$\endgroup\$
    – Maple
    Commented Dec 5, 2021 at 20:23

1 Answer 1


I assume you mean Arduino Uno or Nano with Atmega328p, specify it next time

The best way to figure it out is to look into the datasheet. Of course, if you only have experience with Arduino, it's actually pretty difficult and scary, there are a lot of words you probably never saw or only just saw before. I will try to make a short summary of the important points.

In this case, PD0 and PD1 are actually the serial port pins of arduino. You program arduino through them if you just do it like you always do - 1 cable to pc and nothing else. But you can use those pins for something else, bear in mind tho, you'll need to program arduino with external programmer then. The bootloader starts the serial port for you so you can program the thing comfortably. You need to change bootloader to use them as digital pins, which, unless you have a programmer around just in case something goes wrong and you need to restore the bootloader, I don't recommend you to do.

But if you DO have a programmer around - another arduino as ISP will do - give it a shot, I mean, it's not all that difficult, there's plently of manuals for atmega328(p) bootloaders and stuff. It's like uploading a small program, nothing more, just with a dedicated programmer.

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    \$\begingroup\$ There is not enough information in the OP question to provide a meaningful answer, but that doesn't mean we should provide not-meaningful one. \$\endgroup\$
    – Maple
    Commented Dec 5, 2021 at 20:28

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