Abstract: A method and apparatus for enabling and disabling a pull-up resistor connected to a data line of a universal serial bus is provided for universal serial bus devices that are provided with an external power source. A transistor is interconnected between VBUS of the universal serial bus connection and the input of an integrated circuit such that the voltage on the input of the integrated circuit is proportional to the voltage on VBUS. Thus, when VBUS is not present the pull-up resistor on the data line is disabled and subsequently enabled when VBUS exceeds a predetermined threshold.

Abstract: In a computer system in which a peripheral device is connected to a host computer through two busses each of which has a power supply, a power switching network turns first and second solid state switching devices (FET's) on and off to supply power to the drive. The body diodes of the FET's isolate one power supply from the other and supply power to a controller which turns the FET's on and off. A time constant circuit turns an FET on gradually and a resistor connected between the gate and source of each FET provide enough voltage to turn the FET off if the bus carries a sleep mode signal.

Abstract: A disk drive has an improved ability to detect the presence of a disk cartridge inserted into the drive. The improved disk drive comprises a source of irradiance and a detector of irradiance. When a disk cartridge is inserted into the drive, the detector is optically connected to the source of irradiance by a reflective marker on the cartridge. The emitting surface of the source is oriented such that the irradiance strikes the reflective marker at an angle substantially less than 90 degrees. The detector surface which receives the reflected irradiance is oriented in a manner similar to the emitting surface. This detection system exploits the relatively unique characteristic of certain reflective markers to reflect light in a direction opposite the incident path when the angle of incidence with the reflecting surface is substantially less than 90 degrees.