Patent GB-1242724-A (GB)
Title: Binary data handling system
Inventor: BEHR MICHAEL ISAAC
IPC: G11B20/10
Filed: 1968-09-17
Abstract: 1,242,724. Magnetic data stores. BURROUGHS CORP. 17 Sept., 1968 [18 Sept., 1967], No. 44062/68. Heading G4C. A binary data handling system includes a source of oscillating signals having peaks representing data, means for developing signals representing the positive-going and negativegoing peak-to-peak amplitudes of the oscillating signals respectively, and means for generating an indication each time one of the peak-to-peak representative signals exceeds a threshold value. Modified NRZ (transition for 1, no transition for 0) or phase-encoded binary data from magnetic tape (or disc or drum) 1 is supplied to a high bipolar threshold generator 20 (the output of which switches to 1 when a high positive threshold is exceeded and switches to 0 when a high negative threshold is exceeded, i.e. negatively), a positive threshold generator 21 (which gives 1 when a low positive threshold is exceeded, and 0 otherwise), a negative threshold generator 22 (which gives 1 when a low negative threshold is exceeded, and 0 otherwise), a bipolar peak detector 23 (the output of which switches to 1 at a positive peak, and switches to 0 at a negative peak), and a differentiator 24. With modified NRZ data (flip-flop 40 at "NRZ"), a positive peak exceeding the low positive threshold produces a pulse from AND 43 the start of which causes a pulse generator 42 to supply a pulse to output circuitry 50, as does a negative peak exceeding the low negative threshold, via AND 48. During a write operation, the recorded signal level is checked by reading, an error indication 64 being produced (to cause re-write) if a peak does not exceed the respective high threshold level. With phaseencoded data (flip-flop 40 at "PE"), a preamble of all zeroes produces pulses from pulse generator 42 as with modified NRZ data (using AND 48), a predetermined number of which, as counted at 70, setting a flop-flop 72 to enable gates 73, 74 so that a pulse is produced by pulse generator 42 for each negative peak and by a pulse generator 41 for each positive peak. The differentiator 24 output, symmetrically limited by 75, 76, 85, 86, is applied through oppositelypoled diodes 77, 78 to integrators 79, 80 which thus obtain the positive-going and negativegoing peak-to-peak amplitudes of the original waveform from the tape, respectively. The integrators 79, 80 are reset by the pulse generators 41, 42 respectively. If the (positive) output of integrator 79 exceeds a positive threshold 81 when pulse generator 41 produces a pulse, AND 90 passes the pulse to a first input of output circuitry 94, whereas if the (negative) output of integrator 80 exceeds a negative threshold 83 when pulse generator 42 produces a pulse, AND 91 passes the pulse to a second input of the circuitry 94. Circuitry 94 thus receives a pulse for each 1 at its first input and for each 0 at its second input, all at cell centres, and non-significant pulses at some cell boundaries which the circuitry 94 separates out. It is stated that circuitry 94 may be as in Specification 1,235,547. An error indication 100 is given if the respective threshold 81 or 83 is not exceeded when a pulse is produced from pulse generator 41 or 42. During a write check, such an error causes rewrite, and during reading it causes attempted reconstruction of the lost data using parity information. A postamble is also provided with phase-encoded data.