You are right, I forgot to write that the problem relates to the TTL output pin. In this case TTL is not 5Volt but 3.something volt. And that does not work with a microcontroller running with 5Volt power supply.
Just measure it with a oscilloscope.
Unless the manufacturer has changed this.....
The PIC microcontroller I used does not have USB I/O.
The pin I wanted to use was a TTL input.