A reconfigurable device loads I/O configuration information from a diagnostic interface during testing. The device includes a configurable I/O connection for communicating values with other devices. A diagnostic interface communicates the value of the I/O connection to a tester. A diagnostic controller in the device has a first mode for communicating the value on the I/O connection to the tester via the diagnostic interface, and a second mode for receiving an I/O configuration attribute value for the I/O connection from the diagnostic interface thereby modifying the configuration of the I/O connection. The device also includes a configuration controller that retrieves device configuration information from a configuration device in response to a signal. The signal can originate from an external source or from the diagnostic controller in response to a configuration instruction received via the diagnostic interface. The diagnostic interface may be a JTAG interface.