An I/O pad has a data transmitting circuit, a data monitoring control circuit, and a control selection circuit. The control selection circuit controls the data transmitting circuit at the control end, so as to enable or disable the transmission. When it is enabled, data in the data transmitting circuit are exported to a receiving circuit. When it is disabled, data exportation stops. The data monitoring circuit receives signals of the data transmission circuit and export signals to the control selection circuit. The data monitoring circuit judges whether the data transmission is under a stable condition. If it is not yet, an unstable signal is exported to a first input end of the control selection circuit. A second input end of the control selection circuit receives an output enabling signal. The output end of the control selection circuit is connected to the control end of the data transmitting circuit. When the data transmission is at stable status and the output enabling signal indicates a disable status, the control selection circuit disables the data transmitting circuit. Otherwise, the control selection circuit enables the data transmitting circuit.