Serial issues in my codes

Hello, I am writing from Poland.
I have a little problem with all the Arduino codes and it shows me question marks in the serial monitor. What is my mistake?

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The can mean that you are trying to read from an empty serial input buffer. The read() function returns -1 when there is nothing to read. -1 shows up as the question mark.

The serial input basics tutorial shows robust ways to read data from the serial port.

If you want help with your code post the code. Describe what the code actually does and how that differs from what you want.

Read the forum guidelines to see how to properly post code.
Use the IDE autoformat tool (ctrl-t or Tools, Auto format) before posting code in code tags.

It could mean that the serial line speed in your code doesn't match the serial monitor speed.

Hello, the most important problem has been solved. Bad rs 232 protocol. Now there is some code to write to the inverter.

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