My Opta PLC worked well, but, since I tryed the RS485 sketch from this page https://docs.arduino.cc/tutorials/opta/user-manual/ my Opta PLC does not work.
Now, the reset red led of my Opta blinks 4 times fast and 4 times slow.
When I connect Opta to computer, using USB cable, Windows system displays an error message.
The virtual serial port associated to USB, which was previously recognised, does not work.
I cannot upload any sketch to my opta.
Hi @bqg ,
The behavior of the LED indicates a crash of the Mbed OS. You just need to press the Reset button twice to put the board in bootloader mode (the Reset LED will fade in and out).
In Arduino IDE, a new port will be available, so you can upload a new sketch. 
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Thank you very much @Hm_pro!
The double press on reset button has solved my problem. 
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Is there a way to remotely reset this without having to physically press the reset button? I work with a team that is 12 hours out of phase from me so it's problematic for me to be sitting in front the Arduino Opta to press buttons when the setup was put in place specifically for remote access.