Patent GB-1186926-A (GB)
Title: A Data Transfer System
Inventor: ALAIMO BENJAMIN
IPC: G06F3/06
Filed: 1967-10-31
Abstract: 1,186,926. Digital data recording. MINNESOTA MINING & MFG. CO. 31 Oct., 1967 [1 Nov., 1966], No. 49371/67. Heading G4C. A data transfer system receiving data from a computer or the like and recording it on a moving member comprises a buffer store receiving characters and supplying them in the order received at a rate corresponding to the speed of the record member, means for monitoring the filling state of the buffer store and arranged to control the speed of the moving member in accordance therewith, and control means responsive to a signal from the data source indicating that the supply of data has terminated to cause the moving member to continue to run for a further period of time to provide a gap free of recorded characters. Data from a computer is fed in parallel by bit, serial by character into Write Register 12 under the control of a flip-flop 15 which is reset if register 12 is empty and set if the register has been filled. Each character read out of register 12 passes to a Parity Bit Generator 21 and also to an input register 20, the latter under control of a signal from AND gate 26. Register 20, under control of a clock 31, feeds the character bits out in serial fashion to a recirculating memory 30. Data fed out of memory 30 passes to register 43, under control of flip-flop 45, where it is converted to parallel by bit, serial by character and is fed via a Record Amplifier and Register 55 to Write Heads 51 to be recorded on magnetic tape. Read into and out of the recirculating memory 30 is controlled by counters 32, 35, 36. A bit clock which also feeds AND gates 40, 46, feeds a bit counter. The data is in the form of a six-bit alpha-numeric character having a 7th bit forming a parity bit. The bit counter counts in sevens and then emits a pulse to the character counter 35. An up and down counter is increased when a word is written in memory and decreased when a word is read out. A comparator issues a signal when the contents of the character counter and up and down counter are identical. When the first word is to be read into the memory 30 AND gate is enabled by the IR flip-flop and the comparator (since the store is empty) and 7 bit clock pulses pass. Preferably the period of rotation of the data in the recirculating memory is less than the time between successive characters supplied by the processor. The data is circulated and the character counter incremented causing non-coincidence. When the character counter again reaches one coincidence again occurs with the up and down counter, since the store now holds one character, and a new character can be read in. Whenever the character counter reaches 1, a count 1 detector 47 enables a gate 46 to enable read-out from the store to an output register 43 and also the trailing edge of the " 1 " pulse decrements the character counter and the up and down counter and sets flip-flop 45 to inhibit gate 46 and prevent further transfer to the output register. The character is read out of the register 43 and on to the tape under control of clock signals on line 54 generated from pulses on the tape or from a tach disc driven by the tape. The up and down counter controls the motor via a digital to analog converter 61 which produces a signal representative of the number of characters held in the store and supplies it to a compensating network. This provides the necessary frequency response correction to achieve the required band-width and damping. A signal is then supplied via a summing network 63 to the motor drive. For increasing memory content the motor is driven faster. When a record is complete an end of record character EOR sets a flip-flop 71 and hence flip-flop 72 enables AND gate 73 to increment the up and down counter and blocks the write register from accepting new data. Four all zero characters are read into input register 20 and then the memory under control of the 2kHz clock 74 and then a signal from Count Four 75 causes Write register 12 to generate a longitudinal check character which is also fed into the memory followed by further zero characters. The motor speed is controlled at this period so that rate of read out equals rate of read in. When the longitudinal parity check is detected by detector 81 a flip-flop 83 is set to inhibit transfer of characters to register 55 and to register 43. Flip-flop 72 is reset to prevent further pulses from clock 74 so that decrementing pulses reset counter 36 to zero and a single shot multi-vibrator 85 is set. This produces a signal from a frequency discriminator causing the motor to be accelerated for a short period to produce a gap. The motor is then stopped.