What will be happened if internal clock does not work?

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1

Hello.

I have one question about internal clock of Arduino.

Recently, I made a custom Arduino Nano board. However, when I connect it with USB cable or external power, one of LED is not working - it should be blinked when power is supplied on the board.

I noticed that the malfunctioning yellow LED is linked with SCK (internal clock of microprocessor) like the picture below. The picture was from the interactive viewer of Arduino Nano 33 IoT page.

sck
sck314×360 6.39 KB

If the voltage cannot be supplied on Q1 due to reversed direction of DL1, SCK will not be able to work. Then what will be happened on the board? Can the board work correctly?

2

SCK has nothing to do with "internal microprocessor clock", it is clock signal for SPI and ISP buses only. Internal mcu clock does not connect with any leds.

3

It's not the controller clock but the SPI clock. The LED blinks only during a SPI transmission or with the Blink sketch...