| 摘要 |
1,215,660. Tape readers. NATIONAL CASH REGISTER CO. 9 June, 1969 [27 June, 1968], No. 29056/69. Headings G4C and G4M. A record medium such as punched or magnetic tape has regularly spaced timing marks, e.g. sprocket holes, which are sensed to generate clock signals for sampling the sensed data signals, and the timing marks are also sensed prior to their sensing by the clock generator to produce an error signal upon failure to detect a timing mark at one of the timing mark locations. Sprocket holes 28, Fig. 2, are sensed by a pair of photo-detectors 40, 42, Fig. 1, associated with apertures 34, 36 in a block over which the tape passes in the direction of the arrow, apertures 34, 36 being spaced by more than the distance between adjacent sprocket holes 28. The outputs A, B from detectors 40, 42 are gated together at 52 to produce clock pulses K during their periods of overlap. A further detector 44 associated with an aperture 38 which is spaced from aperture 36 by less than the sprocket hole spacing provides an inverted output F which is gated at 56 with the clock pulses, gate 56 being enabled by strobe pulses S 1 to produce an output G if no sprocket hole 28 is detected by 44 at the time of production of a clock pulse K. A bi-stable 62 may be set to stop sensing. |
