The device (pc) is sending 9-bit packet,
I am sure that it works because if I send a packet with the 9th bit =1, it interrupts, if the 9th bit is=0 it don't.

the device is sending just 1 byte for time. I just made a program that has a button. every click on this button sends a 9-bit packet to the serial port.
I can choose the byte sent, and I can choose if the 9th bit is set or nope.
I also tested it with an oscilloscope. And the 9 bits are correct.