Group coded recording data recovery system
First Claim
1. A digital data recovery system controlled by a system clock for decoding GCR input data bits stored on magnetic media in the form of flux reversals with no more than two successive zeros throughout a data record, comprising:
- a first means for monitoring an input data signal from a magnetic storage media for flux reversals and generating an EDGE signal for each transition of the input data;
a second means responsive to said EDGE signal for enabling the data recovery system when a predetermined number of said EDGE signals have been received and for generating a HLF-EDGE signal when a transition occurs during the first half clock cycle;
a third means responsive to said EDGE signal and a ZONE signal representing the average data rate in clock periods between previous output data bits for comparing the incoming signal with previous output data to signal when to output a data bit as via a RDY-OUT signal and what logical state to give it via a ONE-FF signal;
a fourth means responsive to said RDY-OUT signal for generating a ZONE signal representing the average time between a predetermined number of previous output data bits;
an output means responsive to said EDGE, RDY-OUT, ONE-FF and HLF-EDGE signals for generating an output data bit from said ONE-FF signal and a strobe signal $MRK from said RDY-OUT signal and for generating an error condition pointer signal PNTR and a strobe signal $MRK when a predetermined condition exists between the input data represented by EDGE and HLF-EDGE and the output data represented by RDY-OUT.
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Abstract
This relates to a digital data recovery system for decoding group coded data bits stored on magnetic tape whereon a "1" is represented by a flux reversal and an "0" is represented by the absence of a flux reversal with no more than two successive zeros throughout the data record. Input logic detects transitions of input data and forwards this information to an envelope detector which determines if subsequent transitions represent valid data. The presence of valid data enables a data rate detector which determines the average data rate. An output sequencer determines when a decoded output data bit should be generated and its proper polarity.
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Citations
14 Claims
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1. A digital data recovery system controlled by a system clock for decoding GCR input data bits stored on magnetic media in the form of flux reversals with no more than two successive zeros throughout a data record, comprising:
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a first means for monitoring an input data signal from a magnetic storage media for flux reversals and generating an EDGE signal for each transition of the input data; a second means responsive to said EDGE signal for enabling the data recovery system when a predetermined number of said EDGE signals have been received and for generating a HLF-EDGE signal when a transition occurs during the first half clock cycle; a third means responsive to said EDGE signal and a ZONE signal representing the average data rate in clock periods between previous output data bits for comparing the incoming signal with previous output data to signal when to output a data bit as via a RDY-OUT signal and what logical state to give it via a ONE-FF signal; a fourth means responsive to said RDY-OUT signal for generating a ZONE signal representing the average time between a predetermined number of previous output data bits; an output means responsive to said EDGE, RDY-OUT, ONE-FF and HLF-EDGE signals for generating an output data bit from said ONE-FF signal and a strobe signal $MRK from said RDY-OUT signal and for generating an error condition pointer signal PNTR and a strobe signal $MRK when a predetermined condition exists between the input data represented by EDGE and HLF-EDGE and the output data represented by RDY-OUT. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A digital data recovery system controlled by a system clock for decoding group coded input data bits stored on magnetic media in the form of flux reversals wherein a "1" is represented by a flux reversal and an "0" is represented by the absence of a flux reversal with no more than two successive zeros through the data record, comprising:
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a first means for receiving data from a magnetic storage media in the form of a logic signal which changes polarity as a result of flux reversals on said magnetic storage media, and for eliminating short duration excursions to the opposite polarity which are of a duration less than a predetermined time between two successive flux reversals, said first means also for generating an EDGE signal of a predetermined period for every transition of the input data, and for generating a HLF-EDGE signal of a predetermined duration for every transition of the input data which occurs during the first half of a clock period; a second means for receiving said EDGE signal and for generating an ENV-UP signal to enable said digital data recovery system after a predetermined number of EDGE signals have occurred indicating that data will follow, said predetermined number of EDGE signals corresponding to the number of pulses in the preamble of a data group, and said second means for detecting the termination of said EDGE signals and for terminating said ENV-UP signal a predetermined time later; a third means for receiving said EDGE and ENV-UP signals and a ZONE signal representing the average data rate, said third means for measuring the amount of time between successive EDGE signals and for comparing this with the immediate past history of data output by said data recovery system and with said ZONE signal so as to signal the appropriate time to generate an output signal via a signal RDY-OUT and the polarity of the output via a signal ONE-FF, and said third means for generating a POSN-15 signal indicating that a predetermined number of clock periods have passed since the occurrence of the last EDGE signal; a fourth means coupled to said RDY-OUT, said POSN-15 and said ENV-UP signals for converting said RDY-OUT signal to said ZONE signal representing the average number of system clock periods per data frame where said POSN-15 and ENV-UP signals serve to reset said fourth means if a predetermined condition is met; an output means coupled to said RDY-OUT, ONE-FF, EDGE, HLF-EDGE, and ENV-UP signals for generating an output data signal DTA and for generating a strobe signal $MRK and an error condition signal PNTR, said output means activated by said ENV-UP signal, and for generating said DTA output signal directly from said ONE-FF signal and a corresponding strobe $MRK when a predetermined condition of said ONE-FF, EDGE and RDY-OUT signals occurs, and said output means for generating said error condition signal PNTR upon occurrence of a predetermined condition of said RDY-OUT, EDGE, ONE-FF and HLF-EDGE signals, and for generating said strobe signal $MRK upon occurrence of a predetermined condition of said RDY-OUT, EDGE and ONE-FF signals, said DTA and $MRK signals for use by a host system in determining what data was stored on said magnetic media and said $MRK and PNTR signals for use by said host system in determining whether an error condition during the data recovery operation has occurred.
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14. A digital data recovery system controlled by a system clock for decoding group coded input data bits stored on magnetic media in the form of flux reversals with no more than two successive zeros throughout a data record, comprising:
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a first means for receiving data from magnetic storage media by monitoring a logic signal which changes with flux reversals on said media and for generating an EDGE signal for every transition of the input data; a second means for receiving said EDGE signal and for sensing when a predetermined number of said EDGE signals have occurred and for generating an ENV-UP signal to inform said data recovery system that valid data is coming in; a third means responsive to said EDGE and ENV-UP signals and a ZONE signal representing the average number of clock periods between incoming data bits over a predetermined number of bits in the recent past, said third means for comparing the EDGE signal with said ZONE signal when ENV-UP enables the system in order to predict the actual data written on the magnetic storage media so that the correct time and logical state of the output data can be determined, said third means for signalling the appropriate time for output of a data bit via a RDY-OUT signal and the logical state of this output bit via a ONE-FF signal, and for generating a POSN-15 signal indicating that a predetermined number of clock periods have passed since the occurrence of the last EDGE signal; a fourth means responsive to said RDY-OUT, said POSN-15, and said ENV-UP signals for counting the number of clock periods between each occurrence of said RDY-OUT signal and for storing a predetermined number of said counts as the past history of the data output of said data recovery system and for averaging these counts and for generating said ZONE signal representing the results of said count; an output means active upon activation of said ENV-UP and a data request signal ENABLE from a host system utilizing said data recovery system, said output means responsive to said RDY-OUT, ONE-FF, EDGE and HLF-EDGE signals for converting said ONE-FF signal to an output data signal DTA and for generating an output strobe signal $MRK when said RDY-OUT signal occurs, and for generating an error condition signal PNTR when the relationship between the input data EDGE and HLF-EDGE and the output data RDY-OUT indicates an error might have occurred.
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Specification