I am working on a project, where the Arduino is connected to a programm via serial. Now the only way to debug I have right now is via printing to an LCD screen on the Arduino. However, it would be much easier, to have a second serial connection to the pc. Is this possible via the included usb-serial chip, or would I need an external usb-serial chip to get this to work?
Thank you for any answers
The simplest way is with a USB-TTL cable. You don't say what Arduino board you are using so I can't suggest what pins you should connect it to.
If the PC program is one that you have written yourself then I suggest that you incorporate in it the means to print debug messages from the Arduino - for example all Serial.println() statements that start with "DBG" could be treated as debug messages.
Like Robin2 says, I'd go for modifying the PC software if you can. That way you can use the existing USB serial link from your Arduino to your PC.
If you can't modify the PC software, then a software serial port on another set of pins would be a way to go. You could hook up another USB-serial module and observe its output on your PC. There is a downside to this approach in that it does use up some of the available processor time on your Arduino. This may not be a problem if things are not too time critical in your application.
I assume that you chose a serial port solution because you want to print out some numerical values rather than a simple "I got to here" flag. The latter can be done with LEDs if you have some spare port pins.