Patent ID: 7323898

Claim:
Circuitry for driving a pin, the circuitry comprising: a first resistive circuit connected to the pin; a first transistor circuit to connect the first resistive circuit to a logic level voltage in response to a trigger voltage, the first transistor circuit and the first resistive circuit together defining a termination impedance; a driver circuit to provide the trigger voltage for the first transistor circuit, the driver circuit comprising a second transistor circuit and a second resistive circuit in series with the second transistor circuit, the second transistor circuit and the second resistive circuit together defining a driver impedance that is controlled to control the trigger voltage and thereby control the termination impedance; a switch between the driver circuit and the first transistor circuit; and logic to close the switch and thereby apply the trigger voltage to the first transistor circuit, or to open the switch and thereby prevent the trigger voltage from reaching the first transistor circuit.