Patent ID: 6886052

Claim:
An apparatus for automatically identifying between a USB and a PS/2 interface, comprising: first and second ports being connected to one of a USB interface or a PS/2 interface; a mode selector; a mode detector coupled to said mode selector for detecting a logic state of the first and second ports responsive to a first control signal from said mode selector, said mode detector including (a) a pair of first switching devices coupled to said mode selector and a first positive voltage source, and (b) a pair of first pull-up resistors each having a first end respectively coupled to said first and second ports, a second end of each of said first pull-up resistors being coupled to a respective one of said first switching devices for coupling to said first positive voltage source responsive to said first control signal; a PS/2 mode device coupled to said mode selector and being coupled said first and second ports responsive to a second control signal from said mode selector, said PS/2 mode device including (a) a pair of second switching devices coupled to said mode selector and said first positive voltage source, and (b) a pair of second pull-up resistors each having a first end respectively coupled to said first and second ports, a second end of each of said second pull-up resistors being coupled to a respective one of said second switching devices for coupling to said first positive voltage source responsive to said second control signal; and, a USB device coupled to said mode selector and being coupled said first and second ports responsive to a third control signal from said mode selector, said USB device including (a) a third switching device coupled to said mode selector and a second positive voltage source, said second positive voltage source being at a lower voltage than said first positive voltage source, and (b) a third pull-up resistor having a first end coupled to one of said first and second ports, a second end of said third pull-up resistor being coupled to said third switching device for coupling to said second positive voltage source responsive to said third control signal.