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Bipolar Pulse Positional Priority Recording

IP.com Disclosure Number: IPCOM000073980D
Original Publication Date: 1971-Feb-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Dillon, BC: AUTHOR

Abstract

The circuits shown allow commercial AC audiotape recorders to be used as a memory for storing digital data. An example would be the use of a small cassette recorder with a computer. When in operation, the write circuit shown in Drawing A, generates a special modified Manchester code voltage waveform which is compatible with the tape recorder input. The special modified Manchester code write waveform does not generate a DC voltage component as a function of data as do other RZ or NRZ waveforms, because the Manchester code is basically one full AC cycle for each data bit. During playback, the circuit of Drawing B receives a read signal from the earphone jack of the tape recorder.

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Bipolar Pulse Positional Priority Recording

The circuits shown allow commercial AC audiotape recorders to be used as a memory for storing digital data. An example would be the use of a small cassette recorder with a computer. When in operation, the write circuit shown in Drawing A, generates a special modified Manchester code voltage waveform which is compatible with the tape recorder input. The special modified Manchester code write waveform does not generate a DC voltage component as a function of data as do other RZ or NRZ waveforms, because the Manchester code is basically one full AC cycle for each data bit. During playback, the circuit of Drawing B receives a read signal from the earphone jack of the tape recorder. The read signal will be basically identical to the write signal, with the exception of a loss of high-frequency components due to the low-pass characteristics of an audiotape recorder. The circuit translates the read signal into data signals and also generates a shift-clock signal from the same single-data channel allowing the translated data to be accurately shifted into a shift register for use regardless of the tape recorder's speed variations.

AND gates 11 through 14 of Drawing A generates the special modified Manchester code from data stored in data register 10 under control of clock 1 and clock 2. Positive pulse drivers 22 and 23 provide the positive half-cycles of the Manchester code waveform and negative pulse drivers 21 and 24 provide the negative half-cycles. Summing resistors 31 through 34 sum the pulse driver outputs to form the completed Manchester code waveform across volume-control potentiometer 35. Coupling capacitor 36 couples this signal to attenuator resistors 37 and 38 which attenuate the signal to the level required at the input of most audiotape recorders.

The translate and synchronization circuit of Drawing B receives the read signal from the tape recorder earphone output. Positive level detector 101 and negative level detector 102 reshape and divide the input signal into two square- wave pulse trains. The leading edge of each negative level pulse sets the translate latch 110 to a ONE condition by deconditioning AND gate 112. Each positive level pulse resets translate latch 110 to a zero condition by deconditioning AND gate 111. The ONE and ZERO outputs of translate latch 110 are connected to the data input of data register 140 which may be any register in a digital machine or may be the same register as register 10 shown i...