Control circuit and chipset on motherboard for saving terminal resistors and method for realizing the same

Abstract

A control circuit, a chipset and a method capable of saving the terminal resistors on a motherboard. Through the determination of connection of a pull-up enable line to a first voltage source V via a resistor, an equivalent resistance is set between the source terminal and the drain terminal of a field effect transistor. The equivalent resistance is almost identical to the terminal resistor and hence can replace the resistor on the motherboard. When the pull-up enable line is connected to the first voltage source V via a resistor, an equivalent resistance of about 45-60&OHgr; is established between the source and drain terminal of the field effect transistor. The equivalent resistance is connected in parallel with an input/output pad and a second voltage source V to replace the original externally connected terminal resistor r at the other end of the bus. If the pull-up enable line is not connected to a first voltage source V via a resistor, the field effect transistor is cut off and an infinite equivalent resistance is created between the source and the drain terminal. The infinite resistance is connected in parallel between the input/output pad and the second voltage source V . The infinite equivalent resistance has little effect on any externally connected terminal resistor r at the other end of the bus. Hence, through enabling or disabling the pull-up enable line, manufacturers are free to choose whether to save output power to the terminal resistor r at the other end of the bus or not.