A driver to drive a bus with a pullup and a pulldown transistor according to a data signal during a drive phase and to charge or discharge the bus to intermediate voltage levels during a precondition phase using the pullup and pulldown transistors, the driver comprising a buffer and latch to latch the bus voltage at the end of a drive phase; a precondition circuit responsive to the latch to switch ON a pullup transistor at the beginning of a precondition phase when the bus voltage was LOW in the previous drive phase so as to charge the bus voltage to a first voltage less than a supply voltage, and to switch ON a pulldown transistor at the beginning of the precondition phase when the bus voltage was HIGH in the previous drive phase so as to discharge the bus voltage to a second voltage above ground.