Variable cyclic redundancy character detector

Claim 1

A variable cyclic redundancy character detector for use in a magnetic tape unit used in a data processing system comprising: a. discrimination means for determining whether data or a blank was read from the magnetic tape and what type coding was used in writing the data on the magnetic tape; b. data shifting means connected to the discrimination means for aligning and shifting the data read from the magnetic tape, the data shifting means further comprising a plurality of data registers; c. logic means connected to the data shifting means for determining if the cyclic redundancy character has been read, where it is in the data shifting means, and whether or not the cyclic redundancy character was a blank; d. control signal means connected to the logic means for providing the necessary signals to the logic means to interpret the data being read from the magnetic tape; e. counting means connected to the logic means for varying the time frame for looking for the cyclic redundancy character from the magnetic tape; f. parity checking means connected to the data shifting means for determining the validity of the data read from the magnetic tape and for generating a signal each time a byte of data is read from the data shifting means.

Claim 7

A method of reducing unrecoverable read errors from magnetic tape generally associated with data processing system comprising: a. reading the data record from the magnetic tape; b. aligning each bit of the data byte in parallel; c. detecting whether one or more of the bits of the data byte is a logical one; d. preparing for the reading of a cyclic redundancy character when step c) above indicates an all zero byte; e. inserting a blank cyclic redundancy character if a cyclic redundancy character is not read within a preset number of byte spaces after the last non-zero data byte; f. comparing the computed value of the cyclic redundancy character with the cyclic redundancy character actually read; g. repeating steps a) through f) on the same data record with a different preset number inserted in step e), if the computed cyclic redundancy character value is not equal to the actual cyclic redundancy character value; h. repeating steps a) through g) until the correct cyclic redundancy character is read or it is determined that the data block is invalid; and, i. reading the next data record from the magnetic tape.

Claim 8

A method of reducing unrecoverable read errors from magnetic tape generally associated with data processing system comprising: a. reading the data record from the magnetic tape; b. aligning each bit of the data byte in parallel; c. detecting whether one or more of the bits of the data byte is a logical one; d. preparing for the reading of a cyclic redundancy character when step c) above indicates an all zero byte; e. inserting a blank cyclic redundancy character if a cyclic redundancy character is not read within a preset number of byte spaces after the last non-zero data byte; f. comparing the computed value of the cyclic redundancy character with the cyclic redundancy character actually read; g. repeating steps a) through f) on the same data record with a different preset number inserted in step e), if the computed cyclic redundancy character value is not equal to the actual cyclic redundancy character value; h. repeating steps a) through g) until the correct cyclic redundancy character is read or it is determined that the data block is invalid; and, i. reading the next data record from the magnetic tape.