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Testing Error Detection Circuitry in Tape Units

IP.com Disclosure Number: IPCOM000090687D
Original Publication Date: 1969-Jun-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Breitenbach, RC: AUTHOR

Abstract

Operation of error-detecting circuitry for indicating dead tracks in preambles recorded on magnetic tape is tested by recording special test patterns on the tape to force apparent dead tracks. Reading of these patterns forces an error-detection indication.

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Testing Error Detection Circuitry in Tape Units

Operation of error-detecting circuitry for indicating dead tracks in preambles recorded on magnetic tape is tested by recording special test patterns on the tape to force apparent dead tracks. Reading of these patterns forces an error- detection indication.

Magnetic tape units can include a Start Read Check SRC bit. This is included in a sense byte to flag a dead track within the preamble recorded for synchronizing the readback of recorded data. These preambles are typically 40 bytes long. A phase test is performed during readback of this preamble at any arbitrary time between byte 10 and byte 39. The phase test synchronizes the readback circuitry to be in proper phase for data detection, but must be completed as a required condition before the SRC bit can be set. A tape unit which is placed in a diagnostic mode involves an operation in which recording hardware reacts to any attempt to write consecutive 1's by recording nothing and leaving a blank track instead. This can be selectively performed for any track, any combination of tracks, or all tracks. The following assumes that the system operates with odd parity and, although five tracks are shown, the method is applicable to any number of tracks.

Since it cannot be assumed that the phase test is completed until after the end of 40-byte preamble 10, a special 20-byte section 11 is recorded after 10 to accommodate the SRC bit checking. The recording is effected in diagnostic mode and, therefore, a 1 is inserted in alternate tracks, such as is shown in the first two horizontal tracks, to prevent actual dead tracking in response to consecutive 1's. That is, if all 0's are recor...