Driver Transistor Is Also Called Pull Up. To enable high speed operation the protocol requires that every device connecting to the bus drive the important control signals high for at least one clock cycle before. If we add a pull up resistor instead of a load we get a logic circuit.
If a b and c are all low none of the transistors are conducting i e. Of course the input base or gate to the driver is used to receive the signal while the common pin emitter or source is grounded. With a pull up resistor connected the output still works in the same way as a normal logic gate in that when the output transistor is off open the output is high and when the transistor is on closed the output is low.
Transistor bipolar junction transistor bjt.
Most bjts have enough leakage current that they naturally stay off until a voltage is applied. The pci local bus provides pull up resistors but they would require several clock cycles to pull a signal high given the bus s large distributed capacitance. If a b and c are all low none of the transistors are conducting i e. This condition means that their output is either grounded when low or floating when high so an external pull up resistor rp needs to be connected from the open collector terminal of the pull down transistor to the vcc supply.
