Abstract: To provide accurate measurement of rotational velocity and an adequate bandwidth for servo control as a function of the measurement over a wide range of velocities, the present invention utilizes unique speed computation algorithms based on a combination of fine and coarse shaft velocity measurements from a tachometer. The preferred embodiments utilize control signals derived from the velocity measurements to control motor speed, for example, to provide servo control of a digital tape drive. The preferred embodiments utilize an optical encoder coupled to a reel-shaft to generate tachometer pulses as the shaft rotates. The coarse measurement may actually take two different forms for different speed ranges. In one range, this measurement involves counting the number of pulses in a sampling interval. In the other range, the coarse measurement entails counting the number of sampling intervals per detection of a tachometer pulse.

Abstract: A multiple interface driver circuit for transmitting data in a channel according to one of several different signal protocols. In the exemplary embodiment, two separate bus driver circuits are connected to a common output terminal and may be selected under software control. When one such driver is selected, the other remains in an inactive state, presenting a high output impedance to the driver signal from the other. In an alternative embodiment, one interface driver circuit is connected to the output terminal and the driver circuit output signal is either left unchanged or modified under software control by a second pullup driver circuit. The unconditioned output signal conforms to a first interface protocol. After conditioning by the second pullup driver circuit, the output signal conforms to a second interface protocol.

Abstract: A system and apparatus for startup and speed regulation of low-inertia capstan motors under circumstances where the capstan load during startup may vary widely. A stiction handler provides dynamic control of the motor drive voltage imposed to overcome stationary friction, minimizing the power consumption on startup independently of variations in drag load or motor inertia. A stepped speed-up signal is applied to the motor instead of a conventional constant current-limited signal or sawtooth ramp signal. Motor speed regulation is imposed at each step of a stepped speed-up drive signal. This invention is particularly useful, for example, in low-power magnetic tape drives that must efficiently adapt to variations in drag between one tape cassette or cartridge and another.