An I/O module such as a card reader module for connecting a computer having a first and second USB port is disclosed. The I/O module includes an I/O controller connecting the first USB port, a charging controller connecting the second USB port and a third USB port connecting the charging controller. The I/O controller determines what a power state of the computer is according to communication between the first USB port and the I/O controller and then sends a control signal depending upon the power state to the charging controller. The charging controller changes the third USB port into a pure charger mode without data transfer or a normal mode with both charging and data transfer capabilities according to the control signal.