Circuit, system, and method for preventing a communication system absent a dedicated clocking master from producing a clocking frequency outside an acceptable range

A clock recovery circuit, comprising:

• an oscillator coupled to produce a reference clock that is independent of a bitstream forwarded to the clock recovery circuit;
• a frequency comparator coupled to compare a frequency of the bitstream with a frequency of the reference clock;
• a multiplexer coupled to the frequency comparator to select the reference clock in lieu of the bitstream if the frequency of the bitstream is greater than a threshold value above or below the frequency of the reference clock;
• and
• a phase-locked loop coupled to produce a recovered clock having a frequency substantially equal to the frequency of the reference clock.

A clock recovery circuit, comprising:

• a phase-locked loop coupled to produce a recovered clock from a bitstream received by the phase-locked loop;
• a reference voltage proportional to a frequency of a reference clock;
• a voltage comparator coupled to compare the reference voltage with a voltage value proportional to a frequency of the bitstream;
• and
• a multiplexer coupled to the voltage comparator to forward the reference clock in lieu of the bitstream if the voltage value is greater than a threshold value above or below reference voltage.

A communication system, comprising:

• a first node and a second node interconnected to each other by a communication link, wherein the first node is adapted to place a bitstream of data absent synchronization to a master clock within the first node, and wherein the second node comprises:
• a clock recovery circuit adapted to receive the bitstream of data and selectively produce:
• a recovered clock of substantially variable frequency proportional to a transfer rate of the bitstream during times when a frequency of the recovered clock is within a pre-defined threshold;
• and
• a reference clock of substantially fixed frequency produced from a crystal oscillator during times in which a frequency of said recovered clock exceeds or is less than the pre-defined threshold, wherein the reference clock is produced only during times when a number of data bits transferred between preambles of a frame of said bitstream exceeds or is less than a pre-defined amount.

A method of transferring data, comprising:

• producing a reference clock during power-on reset of at least a portion of a communication system;
• synchronizing the data to the reference clock;
• and
• terminating the reference clock, and generating a recovered clock from the data and forwarding the recovered clock to a digital subsystem in lieu of the reference clock.