This is more of an informational note to anyone designing their own board with a Tiva processor and using the USB as a virtual com port (e.g. CDC mode). If any of my interpretations are wrong, please don't hesitate to correct me.
We based our board on the LaunchPad (EK-TM4C123GXL) and connected the USB port of U1 on the schematic as shown in spmu296.pdf. However, we failed to notice that the UART Rx/Tx pins on the UART (VCP_RXD and VCP_TXD) are connected to the UART Rx/Tx pins on the ICDI chip, U2. I don't know what goes on in that chip, but suspect that the Rx just echoes the Tx character.
On our board we connected the Rx and Tx pins together to get the Virtual COM port working in this example. This means that 4 pins are required from the processor to implement this example; 2 pins for the USB and 2 pins for the UART.
Hope this helps anyone else designing their own board.