multiple constant drivers error

Hello,

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I saw that the "when" in my case dont stop. That's make a big looping which never stop.

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That's exactly, what I read from the code. After reset, it cycles between the two states. You won't name it a finite state machine normaly. It's just a one bit binary counter with a reset and an output (LCD_EN) depending on.

If you intend a more complex functionality (most likely), you should define additional input signals, that conditionally enable the state switch, e. g.:

IF input_condition = '1' THEN
  etat_suiv <=ECRITURE2;
END IF;

You can consult the VHDL state machine templates in Quartus HDL editor context menu for an example. Basically, this isn't a matter of HDL coding rather than how you define your design's functionality.

Regards,

Frank