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Character Gating for NRZI Recording

IP.com Disclosure Number: IPCOM000075790D
Original Publication Date: 1971-Nov-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Hinz, HC: AUTHOR

Abstract

Generally, magnetic tape multitrack NRZI character gates are set at approximately 50% of the nominal bit period between successive character transitions. Under certain skew and velocity conditions, during a readback operation, it is possible for the readback circuits using the above-mentioned character-gating techniques in a multitrack system to indicate extra bytes of data. Such extra bytes are introduced when the skew between bits of a character or byte introduces an elapsed time between bits in one character exceeding the character-gate duration. This condition is called "byte splitting". That is, a transition occurring after termination of the character gate initiates an additional character gate which is undesired, and which erroneously introduces an apparent extra byte in the record.

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Character Gating for NRZI Recording

Generally, magnetic tape multitrack NRZI character gates are set at approximately 50% of the nominal bit period between successive character transitions. Under certain skew and velocity conditions, during a readback operation, it is possible for the readback circuits using the above-mentioned character-gating techniques in a multitrack system to indicate extra bytes of data. Such extra bytes are introduced when the skew between bits of a character or byte introduces an elapsed time between bits in one character exceeding the character-gate duration. This condition is called "byte splitting". That is, a transition occurring after termination of the character gate initiates an additional character gate which is undesired, and which erroneously introduces an apparent extra byte in the record. If such an extra byte is introduced, the CRC (cyclic redundancy check) used to identify tracks in error cannot point to a track (the CRC is dependent upon having a correct number of data bytes). When the CRC cannot point to a track in error, errors in the record become permanent.

The extra byte caused by excessive skew velocity combinations Can be eliminated. An auxiliary gate is established for a predetermined portion of the bit period following the termination of the character gate. If a transition or data bit is detected during the auxiliary gate time, the data bit is stored; while an additional character gate is inhibited. That is, the auxiliary gate prevents initiation of another character gate for a preset time after termination of the immediately preceding character gate. The detected transition or data bit, by the auxiliary gate, is processed and stored with the subsequent charac...