Browse Prior Art Database

Multiple Use of Timer For Flexible File Control

IP.com Disclosure Number: IPCOM000048048D
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Quinlan, WP: AUTHOR

Abstract

In a flexible disk control three dedicated hardware units are replaced by software manipulation of a counter. One short term and two long term timing functions must be performed: erase gate delay, spindle motor tachometer (tach) period, and spindle motor pulse-width modulation (PWM).

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Multiple Use of Timer For Flexible File Control

In a flexible disk control three dedicated hardware units are replaced by software manipulation of a counter. One short term and two long term timing functions must be performed: erase gate delay, spindle motor tachometer (tach) period, and spindle motor pulse-width modulation (PWM).

A single module microprocessor with an external crystal controlled frequency is used to drive an internal counter. The counter is a preloadable up counter which interrupts on overflow (255 approaches Phi).

The spindle motor has an integral tachometer which provides spindle velocity feedback. The microprocessor continuously samples the line for period measurement. The internal counter is preloaded with a count which determines the low time of the PWM of the spindle motor driver. After this time, which is always a fraction of the tach period, the high time is started and continued until the start of the next period, which repeats the cycle. In this way a microprocessor generated duty cycle is applied to the spindle motor.

The tach period is being measured at the same time by storing the start count and the end count, when the tach period ends. If the number of overflows of the counter is correct, then (256 - starting count) plus end count equals tach period. This number is used to calculate the speed error and adjust the duty cycle.

If the duty cycle overflows (to greater than 100 percent) or underflows (to less than 0 percent), since the...