Patent GB-867603-A (GB)
Title: Improvements in or relating to information reading arrangement
Inventor: SHARP JOHN JOSHUA
IPC: G11B20/18
Filed: 1957-04-24
Abstract: 867,603. Electric digital-data-storage apparatus; electronic counters. INTERNATIONAL COMPUTERS & TABULATORS Ltd. March 5, 1958 [April 24, 1957], No. 13043/57. Class 106 (1). Apparatus for transferring blocks of data from a tape to a utilization device, comprises tape-sensing means and means for feeding the tape in a forward direction or, in certain circumstances, in reverse. General.-In the apparatus shown, characters are recorded across a magnetic tape 102, Fig. 1, in a 7-bit code (6 information bits, and 1 parity check bit to make the total number of " 1 's " odd). A " record " on the tape comprises a first block of identification characters and a second block of characters to be printed in device 6, Fig. 4, each block being followed by a special " block end " code character, and the blocks being separated by a gap code (all " 1's "). Each of the 7 tracks is sensed by a head 101 connected to a similar reading circuit including a pre-amplifier 103, Fig. 1, whose output for each bit is one cycle of a sine wave, Fig. 3A, with the first half-cycle positive for " 1 " and negative for "0." This output is applied to a transformer having a centre tapped secondary so feeding amplifiers 105, 106 that they produce positive pulses, Fig. 3, B and C, corresponding to the positive and negative peaks of the sine wave respectively. The differentiated output of amplifier 105 triggers a monostable circuit 108 thus producing a lengthened pulse, Fig. 3, D, on line 110. This pulse is used to gate the output of amplifier 106 to line 111. Thus a pulse appears on this line, Fig. 3, E, only if the pulse from 106 occurs after the pulse from 105, i.e. if a " 1 " is sensed. When a pulse occurs on any of the lines 110, Figs. 1 and 2, Or gate 113 produces an output which generates a clock pulse on line 4. The " 1 " bits on lines 111 are set up on shift register stages 126 and shifted by pulses from source 144 into further shift register stages (Fig. 5, not shown), associated with a 6-bit diode matrix decoder 3, Figs. 2 and 4. For each decoded character, a gated output pulse appears on a corresponding line 50 connected to a column of a magnetic matrix buffer store, e.g. as described in Specification 867,604, in printing device 6. Scale-of-seven counter.-The shift pulses from 144, Fig. 2, are applied through gates 131, 132 to a counting chain comprising bistable triggers 128-130. Outputs from the triggers so control the gates that _the first pulse is passed through 132 to the second stage 129 but subsequent pulses pass through 131 to the first stage 128; the triggers thus receive an initial entry of " 2 " and then count in normal binary fashion, an output thus being obtained from 130 after 7 shift pulses have been applied. Tape control unit.-The tape 102, Figs. 1 and 6, is fed forward past reading head assembly 54 by energizing reel drive motor 60 and forward drive solenoid FC, and is similarly fed in reverse by energizing motor 61 and solenoid RC. When the tape is at rest, relay R34 is energized through contacts FCa, RCa and closes contacts R34a (relay gate 34, Fig. 4) so that a pulse on line 7 from the printing device 6 starts forward feed, the circuits to solenoid FC and motor 60 being held through contacts STa of relay ST. Forward feed continues until a reversing pulse is applied on line 21, 31 or 38 to energize a relay NR, ER and RR which closes hold contacts NRa, ERa or RRa respectively. A circuit is then completed through switched contacts FCb to relay SP to open contacts SPa in the forward drive hold circuit, and then to the reversing motor 61 and solenoid RC, the reverse feed operating for a time determined by thermal delay contacts 74, 77 or 78. Normal operating sequence.-At the start of the normal cycle for reading and printing a single record the tape is at rest with approximately the middle of the second block of the previous record under the reading heads. On completion of the previous printing cycle, contacts 22 in device 6, Fig. 4, close to send a pulse over line 7 to the tape control unit 20. The tape is then driven forward, and, as each character is read, it is passed via shift register 126, Fig. 2, to decoder 3; also, the output of counter trigger 130, after delay in networks 135, 137, supplies a pulse on line 49 which is gated to the appropriate decoder output line 50, but this has no effect on the printer. When the block end code character is detected, decoder 3 triggers a monostable circuit 9, Fig. 4, which supplies a setting pulse to a bistable trigger 10 acting as a binary counter. At the end of the first block of the following record, circuit 9 is again triggered and resets trigger 10 which then applies a setting pulse to a " record start indicator " trigger 11. Triggers 10 and 11 open gate 12, so that the clock pulses on line 4, one for each gap code character, are passed to counter 14. At the end of the gap, counter 14 closes gate 13 and opens gate 15 whereby subsequent clock pulses one for each of the characters to be printed, are passed to device 6. The gated pulses on character lines 50 corresponding to the second blocks of the record to be printed are distributed under control of these clock pulses, to appropriate positions in the magnetic buffer store. At the end of this second block, trigger 10 is again set and sends a pulse via gate 18 and line 25 to reset counter 14 and to start a scanning and printing cycle in which the characters in the buffer store are printed out. The output of gate 18 is applied also via gate 19 to line 21, Fig. 6, to reverse the tape to approximately the middle of the second block of the record which has just been read.. During this reversal, the block end code is again sensed, thus causing triggers 10 and 11 to be reset in preparation for the next cycle. Detecting and correcting errors.-An error trigger 5, Figs. 2 and 4, is set through gate 117 136 if a sensing error or parity checking error is detected. Gate 117 receives the clock pulses from OR gate 113, delayed by trigger chain 120, 122, 124 and is opened by inverter 116 if AND gate 114 is not operative; thus an error is indicated if pulses occur on some but not all of the lines 110. Gate 136 is controlled by a trigger 138 which acts as a binary counter for the "1's" shifted out of register 126; if the number of "1's" is even, trigger 138 is unset and gate 136 open at the time a pulse is received from delay network 135. At the end of the reading of the second block of the record to be printed, if an error has been detected, trigger 5 inhibits the printing device 6 and diverts the output of gate 18 through gate 27 (instead of 19) to gates 29 and 30. If an error code character has been detected, indicating that an incorrect record on the tape is followed by a correct record, trigger 24 has been set by decoder 3 and opens gate 29 whose output resets triggers 5, 24 and 11. The tape then continues to be driven forward and the correct record is read and printed in the normal way. If error code trigger 24 is not set, it opens gate 30 whose output, as well as resetting triggers 5 and 11, pulses tape-reverse line 31, Figs. 4 and 6, which causes the tape to be reversed to the point at which reading began. A second reading and printing cycle is then attempted. If an error is repeatedly detected a visual or audible warning signal may be given. The failure of the reading circuits to read one or more characters can also be detected, since less clock pulses will be passed to line 4 and the buffer store in device 6 will not be filled. In these circumstances at the end of the block read, a signal on line 35 inhibits gate 19 and passes through gate 36 to tape-reverse line 38 which causes the tape to be reversed to the beginning of the block for a further reading operation, the output of gate 36 being applied also via inverter 16 and delay 32 to reset the trigger 11. Circuit details.-Circuit diagrams are given for most of the elements shown in Figs. 1 and 2, the circuits including double triode trigger circuits and shift register stages and pentode gates.. Modif´cations.-Information may be recorded on the tape in groups of records each group being followed by a " back-end " code which causes the tape to feed forward to the next group. The first identification block of a record may be omitted, or a record may comprise more than two blocks. The magnetic tape. recording may be replaced by marks or holes sensed by photo-electric cells or brushes. The recorded information may be transferred to a computer or punching mechanism in place of a printer. Specifications 812,934 and 848,326 also are referred to.