TX RX pins work, usb doesn't

Hi, I am trying to communicate between my Arduino and Raspberry pi over serial. I have a duemilanove and uno to work/test with. It works great when i feed the data into the TX RX ports on the Arduino. I would like to communicate over usb so I sent the data into the USB data pins. So far this has been unsuccessful. I know the data is entering the usb correctly because it works when I add a jumper between the TX RX pins the the usb solder joints on the board. While trying to find an answer, I ran across this - http://playground.arduino.cc/Main/DisablingAutoResetOnSerialConnection I don't know if it is related to my problem. I followed the steps with no avail. More specifically, I tried adding the resistors to both the duemilanove and uno. I also tried the the 10uf capacitor on the uno. Does anyone know why this might be happening? Any Suggestions?

Thanks!

If you want to communicate over USB then you need the USB host to provide USB drivers that can handle the Arduino serial-over-USB protocol. If the Arduino IDE works on your host then it probably already has suitable drivers installed.

Whatever you think you might have achieved by connecting the USB pins to the serial TTL pins, it was nothing to do with USB.

So if I understand you correctly, the data that goes into TX and RX pins is different than the data entering the USB, d+ d-, pins.

mattt4001: So if I understand you correctly, the data that goes into TX and RX pins is different than the data entering the USB, d+ d-, pins.

It is completely different. USB is based on a complex message-based protocol that is vastly different to the simple digital square wave of an async serial stream.

Fortunately your Arduino has a USB driver that can handle the USB protocol for you and presents the interface as a simple serial port. Whatever the 'host' end of the USB is connected to would need to provide a corresponding USB driver which deals with the USB message protocol and again presents the interface as a (virtual) serial port within the host. If the host platform is supported by the Arduino IDE then you should already have suitable drivers available. If it isn't supported then I suggest you look for solutions that do not involve USB.