| 摘要 |
Binary information recorded on magnetic tape is read from the tape and tracked in a manner which is independent of the data pattern on the tape. The time displacement error, TDE (used hereinafter interchangeably) between the data pulses from the tape and a phase-locked-loop reference signal is sampled and then held until the next subsequent opportunity at which the data from the tape can be updated. The TDE between a read binary one and a reference signal is measured by counting a plurality of reference pulses occurring between a reference edge marking the beginning of a data time window and the time at which a binary one is read from the tape. The accummulated count is sampled by a counter whose contents are then stored in a latch when the total TDE has been measured. The TDE in the latch is then used in the phase-locked-loop circuit to adjust the frequency of the reference signal to more nearly match the frequency of the data read from the tape. Thus, whenever a binary one is read from the tape, the TDE is measured, stored and used until the next binary one is read and the time displacement error can then be updated.
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