An output driver includes control logic configured to switch on a pull-up circuit and a pull-down circuit to provide an output impedance for a logic low on a transmission line. The output driver includes a variable pull-up resistor. The control logic is configured to switch on the pull-up circuit to a first value of impedance to drive a logic high on the transmission line. The control logic is configured to switch on the pull-up circuit to a second value of impedance and to switch on the pull-down circuit to provide the output impedance to drive a logic low on the transmission line. The system could alternatively be configured for the inverse to switch on a combination of pull-up and pull-down circuits for a logic high, where the pull-down circuit is switched on for a logic low.