Patent GB-1177520-A (GB)
Title: Reader for Reading a Record Bearing Recorded Signals.
IPC: G11B20/16
Filed: 1967-09-07
Abstract: 1,177,520. Tape readers. INTERNATIONAL BUSINESS MACHINES CORP. 7 Sept., 1967 [14 Sept., 1966], No. 40870/67. Headings G4C and G4M. A counter is advanced in synchronism with the scanning of a row of data on a record, e.g. a magnetic or punched tape, the sensed signals being entered in a store at locations determined by the state of the counter. Reader operations other than sensing of data are selected by the counter when set to states other than those occurring during scanning. Tape sensing and feeding.-Each character, including a parity bit, is recorded across the tape 12 and one track is reserved for a start bit or bits signifying the start of a message. The bits may be recorded obliquely so that they are detectable when transducer 11 is being scanned across the width of the tape or when transducer 11 is stationary and the tape is being fed longitudinally. In a normal read operation, tape 12 is advanced character by character by a solenoid-operated pawl and ratchet mechanism, Fig. 4 (not shown), and between feed steps a clutch is energized to couple shaft 16 to a cam 19 driving a slide 20 on which transducer 11 is mounted, so that each character is scanned serially by bit across the tape. During the scanning movement of transducer 11 a magnetic or photo-electric emitter 21 produces two interlaced trains of timing pulses A, B, each bit pulse from transducer 11 occurring between an A and a B timing pulse. Timing pulse counter. Fig. 7a (not shown), comprises a set of latches responsive to the A, B timing pulses to assume 10 successive state combinations and settable manually to further state combinations when other reader operations detailed below are selected. The states 1-9 of the counter gate the corresponding bits sensed by transducer 11 into the appropriate stages of an output register coupled to data processing apparatus. Several tape readers may be associated with the D.P.A. Parity check and read out.-When a character has been read, the counter assumes state 10, and provided a parity check is satisfied a character ready signal is transmitted to the D.P.A. to read the output register, e.g. 4 bits at a time. State 10 also causes the tape stepping solenoid to be energized. When the D.P.A. has received a character it may generate a read command which causes the output register to be reset and initiates scanning of the next character. Load operation.-Pressing the load key causes the tape step drive to be released and a continuous drive to be clutched in until a switch detects the tape leader portion. The tape is then incremented and scans are made by transducer 11 until a special code signifying the start of a message is detected in the output register. The initial tape run-in is performed with the counter in state 15, but the counter is stepped through states 1-10 for each subsequent scan by transducer 11 as in a read operation. Search operation.-The counter is set to state 14 and this initiates a scan by transducer 11 and continuous drive of the tape. When transducer 11 is returning from its first scan, it is arrested over the search track by a solenoid-operated detent and remains in this position until a search bit signifying the start of the next message is detected, whereupon the detent is released to allow transducer 11 to return to the home position and the tape is stopped. Thereafter, the tape is incremented and scanned until the special code is detected as in the load operation. Re-read operation.-Detection of a parity error lights a lamp and the operator can cause re-scanning of the same character by setting the counter to state 0 which initiates a fresh scan by transducer 11 after re-setting the output register. Unload operation.-The counter is set to state 13 causing the tape step drive to be released and a two-torque clutch to apply a higher torque than its normal reverse bias so that the tape is driven backwards until the leader section is sensed by a switch.