1. A circuit for reading digital data from and for writing digital data to a video cassette tape of a video cassette recorder (VCR) having a plurality of manually operated switches, said circuit comprising: means for inputting digital data from a data channel and for outputting digital data to said data channel; means for decoding said input data into commands and data, said decoding means generating a write command causing digital data from said data channel to be written on said cassette tape, a read command causing digital data from said cassette tape to be read by said data channel, and operational commands causing functional operation of said VCR: said decoding means including: a shift register for transforming a serial command into a parallel command word, said shift register inputting said serial command as a plurality of bits from said input data and generating said command word from its outputs; means for clocking said shift register with a predetermined number of clocking pulses in order to input a serial command of that number of bits, wherein said clocking means is enabled by the first bit of a command and is disabled by a counter means which counts the number of clocking pulses applied to said shift register; a run monostable which is set by the receipt of input data and generates a run signal to enable said clocking means, said run monostable being continuously retriggered by incoming data until an entire command has been received and then timing out, said run monostable generating a halt signal upon timing out disabling the clocking means, clearing said shift register, and resetting said counter means; a character decoder for decoding bit positions of said command word into strobe signals on control lines; said decoding means generating said read command on one of said control lines, said write command on another of said control lines, and said operational commands on other of said control lines; a plurality of relays, each having a coil and switch contacts; wherein said control lines generating said operational signals are each coupled to one of said plurality of relays such that each control line drives the coil of a corresponding relay and each relay has its switch contacts connected in parallel across one of said manually operated switches of the VCR; means for writing said digital input data on said cassette tape in response to said write command; means for reading said digital output data from said cassette tape in response to said read command; a read bistable which can be set by the read command and whose output enables said means for reading; and means for operating said video cassette recorder in response to an operational command.
1. A circuit for reading digital data from and for writing digital data to a video cassette tape of a video cassette recorder (VCR) having a plurality of manually operated switches, said circuit comprising: means for inputting digital data from a data channel and for outputting digital data to said data channel; means for decoding said input data into commands and data, said decoding means generating a write command causing digital data from said data channel to be written on said cassette tape, a read command causing digital data from said cassette tape to be read by said data channel, and operational commands causing functional operation of said VCR: said decoding means including: a shift register for transforming a serial command into a parallel command word, said shift register inputting said serial command as a plurality of bits from said input data and generating said command word from its outputs; means for clocking said shift register with a predetermined number of clocking pulses in order to input a serial command of that number of bits, wherein said clocking means is enabled by the first bit of a command and is disabled by a counter means which counts the number of clocking pulses applied to said shift register; a run monostable which is set by the receipt of input data and generates a run signal to enable said clocking means, said run monostable being continuously retriggered by incoming data until an entire command has been received and then timing out, said run monostable generating a halt signal upon timing out disabling the clocking means, clearing said shift register, and resetting said counter means; a character decoder for decoding bit positions of said command word into strobe signals on control lines; said decoding means generating said read command on one of said control lines, said write command on another of said control lines, and said operational commands on other of said control lines; a plurality of relays, each having a coil and switch contacts; wherein said control lines generating said operational signals are each coupled to one of said plurality of relays such that each control line drives the coil of a corresponding relay and each relay has its switch contacts connected in parallel across one of said manually operated switches of the VCR; means for writing said digital input data on said cassette tape in response to said write command; means for reading said digital output data from said cassette tape in response to said read command; a read bistable which can be set by the read command and whose output enables said means for reading; and means for operating said video cassette recorder in response to an operational command. 12. A circuit as set forth in claim 1 wherein said means for writing further includes: means for writing said digital input data to one channel of said cassette tape in response to a write command; means for writing said digital input data to another channel of said cassette tape in response to a write command; and means for inverting said digital input data before it is written by one of said means for writing.