Advanced Micro Devices Corporation

Frederic J Hirzel

Roy J Levy

A method for rapidly recovering the clock from Manchester-encoded signals using simple digital techniques is provided for use in an inexpensive Manchester-encoding receiver. The received Manchester-encoded signal is monitored to determine zero-voltage crossing. At each such crossing the frequency of the recovered clock is adjusted by comparing the occurrence of the zero-crossing with respect to the midpoint of the period of the presently-generated recovered clock. Shorten, center or lengthen adjustment signals are generated as a result of this comparison which are used to shorten or lengthen, by 1/16 increments of the inter-bit period of the received data signal, the period of the next-generated recovered-clock. The method is readily implemented as a sixteen-stage programmable counter providing a phase-locked loop.

Method for digital clock recovery from Manchester-encoded signals

A signal pre-processing method for detecting valid Manchester-encoded activity on a line carrying Manchester-encoded data signals to an inexpensive Manchester-decoding receiver. Detection is provided by monitoring both a positive-level presence and a negative-level presence to determine whether the received Manchester-encoded signal exceeds a predetermined positive voltage or falls below a predetermined negative voltage. Following detection of such line activity, the received signal is determined to be validly Manchester-encoded if it first crosses a predetermined positive level or a predetermined negative level after having first previously crossed the opposite level within a time interval of 3/4 to 11/4 of the inter-bit period of the received data signals.

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Cupertino, CA, United States of America

Frederic J Hirzel