10. A circuit as set forth in claim 9 wherein said write channel selecting means includes: a write channel select bistable having an output and an inverted output which are used alternately to enable said one and said another write channels, saiJ write channel select bistable being toggled to change states n response to write channel select command from one of said control lines.
9. A circuit as set forth in claim 1 wherein said means for writing further includes: means for wirting said digital input data to one channel of said cassette tape in response to said write command; means for writing said digital inpu data to another channel of said cassette tape in responsc to said write command; and means for selecting between said onc and said another write channels to apply said input data from said data channel.