Integrated circuit with multi-function controlled impedance output drivers

A multi-function output driver that may be used with at least two types of busses includes a multiplexer that shifts calibration bits to the pull-down transistors. This shifting changes which transistors of the transistor array are turned on when the pull-down drive transistors are driving. By changing which transistors are turned on, the impedance of the driver is changed. This shifting is used with a disable function on the pull-up drive-transistors to allow the driver to be used as an end-of-line termination, an open-drain driver, or as a source-terminated driver.