A simplified representation of a bidirectional transmission line with I/O transceiver cells is shown. The drivers are open-drain n-channel devices and the receivers are differential comparators. When all drivers are inactive, the high-level signal is established by the terminator supply voltage. The loaded characteristic impedance of stripline signal traces on a printed-circuit board can be about 50 Omega . When there is more than one driver, the transmission line must be terminated at both ends to prevent reflections. System arbitration allows only one driver access to a line at any time. The load seen by each driver is about 25 Omega . The power dissipated is reduced if the signal voltage swing and the Vol level are small. The minimum voltage swing must be large enough to assure acceptable noise margin.<>