A process is disclosed for communicating digital data between a powered device and a charging device via a universal serial bus (USB). The process includes conducting a handshaking period between the powered device and the charging device via the USB. The powered device initiates a mode of normal operation of the charging device after an end of the handshaking period. The charging device communicates digital data (e.g., available power levels) between the powered device and the charging device during a time period that starts with the end of the handshaking period and ends with a beginning of the mode of normal operation.