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Skew-Indicating Circuit

IP.com Disclosure Number: IPCOM000042728D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 30K

Publishing Venue

IBM

Related People

Fiorino, BC: AUTHOR

Abstract

The skew-indicating circuit permits a skew check with a master skew tape. Data from the outside tracks are directed to a phase detector and a frequency discriminator with the outputs of both directed to an AND gate. The phase can be checked when the drive is at the correct speed and the check skew circuit has been enabled. The output of the AND gate is directed to a digital-to-analog (D/A) converter. The output of the D/A converter is directed to a threshold detector whose output is directed to a latch flip-flop. If one or both of the input tracks are bad due to a defect, a skew error is detected. The term "skew" in tape systems refers to the alignment of bits of information in a parallel byte of data.

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Skew-Indicating Circuit

The skew-indicating circuit permits a skew check with a master skew tape. Data from the outside tracks are directed to a phase detector and a frequency discriminator with the outputs of both directed to an AND gate. The phase can be checked when the drive is at the correct speed and the check skew circuit has been enabled. The output of the AND gate is directed to a digital-to-analog (D/A) converter. The output of the D/A converter is directed to a threshold detector whose output is directed to a latch flip-flop. If one or both of the input tracks are bad due to a defect, a skew error is detected. The term "skew" in tape systems refers to the alignment of bits of information in a parallel byte of data. A byte of data is composed of a plurality of bits of information which are written simultaneously across the width of the tape. For a particular byte of data, skew is defined as the earliest bit in the byte as compared to the latest bit in the same byte as read from the tape. The skew-indicating circuit, as shown in the figure, permits the checking of the skew. A master skew tape is placed in the drive when checking the skew of the drive system. As shown in the figure, data from the outside tracks is directed to an AND gate 1 and to a phase detector 2. The output of the AND gate 1 is directed to a frequency discriminator circuit comprising a band-pass filter 3 and a Schmitt trigger circuit 4. The output of the Schmitt trigger is directed to another AND gate 5. The phase detector 2, which could be an exclusive OR circuit, emits an output only if the pulses from the opposing tracks are out of phase. The output of the phase detector 2 is directed as another input to the AND gate 5. Also included as an input to AND gate 5 is a line identified as "speed" which is activated if the tape drive has reached its operational speed. The fourth input to the AND gate 5 is identified as "check". This input activates the checking of the skew. The output of the AND gate 5 is directed to a digital-to-analog converter identified as a low-pass filter 6. The output of the low- pass filter 6 is directed to a voltage comparator 7, which compares the input voltage to a...