Why does the PIN 13 LED of Uno R3 blink every time I upload some code?

Question

I was driving a relay from Arduino Uno R3 Pin 13. I observed that every time I upload some code the led on the board designating pin 13 would blink. I'm curious why this is so. I understand that the serial LED blinks cause there's a serial transmission but why an IO pin?

score 4 · Answer 1 · edited Apr 13 '17 at 12:50

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See What happens when code is uploaded using the bootloader? - the flashing is by design.

Probably the reason is to confirm that the bootloader has started.

edited Apr 13 '17 at 12:50

Community

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answered Oct 14 '15 at 06:10

Nick Gammon

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score 1 · Answer 2 · answered Oct 14 '15 at 05:19

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It's driven by the bootloader, which is performing the flashing (I suppose you are flashing through the USB port).

answered Oct 14 '15 at 05:19

Igor Stoppa

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score -1 · Answer 3 · edited Oct 18 '15 at 09:07

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To show that the bootloader is functioning satisfactorily to the hobbyist. Boot loader helps to upload new sketch on the chip.

edited Oct 18 '15 at 09:07

Butzke

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answered Oct 15 '15 at 17:44

PRADEEP MODAK

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Why does the PIN 13 LED of Uno R3 blink every time I upload some code?

3 Answers3