A communications apparatus is provided having a first line driver transmitting data at a first end of a serial bus to a second line receiver at a second end of the serial bus. A first line receiver receives data at the first end of the serial bus from a second line driver at the second end of the serial bus. The first line receiver has a selectable input parameter that controls a physical layer quality of data received at the first end of the serial bus. Programming instructions stored in memory cause the second line driver to transmit a training signal that is not a COMWAKE signal to the first line receiver in response to the first line driver transmitting a COMWAKE signal to the second line receiver. A controller compares a received physical layer quality of the training signal at the first line receiver to a desired physical layer quality and computes a value for the input parameter to obtain a desired physical layer quality.