Embodiments of the invention include a data buffer for connecting a core of a data circuit to a data pad. External devices may couple to the data pad even if they have a different power supply voltage than does the core of the data circuit. A pass transistor is coupled between the data pad and a data node in the buffer. A control circuit monitors a signal on the data pad and drives the pass transistor according to the signal received, thereby preventing damage due to voltage mismatch between the data circuit and the external device.