GB1259938A - Magnetic recording apparatus - Google Patents

Abstract

1,259,938. Self-clocking digital recording systems. INTERNATIONAL BUSINESS MACHINES CORP. 13 Nov., 1970 [22 Dec., 1969], No. 54009/70. Heading G4C. A multi-track magnetic recording system ineludes a number of clock pulse generators, each associated with a respective track and being synchronized by self-clocking data read from the track. In the absence of data signals from a track the associated clock generator is synchronized by signals from one of the other tracks. In the embodiment illustrated there are 4 tracks and associated read/record channels 10- 13 connected to unit 18. Each channel is similar to that shown at 10 and comprises a data detection circuit 26, which passes data from the record to unit 18, and a synchronizing circuit including clock generator 29 which passes clock pulses to circuit 26. The signals from the associated track pass via gates 41, 44 to synchronize generator 29. Unit 32 detects the amplitude of the signal from the track and if it falls below a certain level, e.g. due to tape lift-off, it passes a signal to unit 18, which subsequently inhibits circuit 26. It also switches latch 40 to inhibit generator 29, inhibits gate 41, and enables counter 45 and gate 42. Gate 42 now passes signals from another track, preferably the adjacent track, both to the generator 29 and to counter 45. Upon the arrival of the third pulse from the new track, counter 45 switches latch 40 to its original state, so enabling generator 29 which now generates clock pulses synchronized by the signals from the new track. When data signals are again sensed by unit 32 a similar switch process occurs, the generator being inhibited until the third pulse from the associated track. If, when the signal in one track fails, the signal in the adjacent track also is absent the synchronizing signals are derived either from another track or from the clock pulse generator associated with another track. The frequencies of the track signals may be averaged to provide a sync. signal.