TRS 80 cassette interface rediscovered - recorded data cleaner

7-30 — elektor july/august 1982 The TRS 80 computer is a fairly good machine, but the cassette interface has already driven many an owner to the depths of despair. Why the tapes are read back so unreliably has never been worked out, but despite this fact there are a number of suggestions on how to improve matters. The circuit given here also produces good results, but as with so many good suggestions we do not really know why. The TRS80 records clock pulses and data pulses on the tape at a constant amplitude. The time interval between pulses is 2.4 mS. The logic is written by inserting a pulse between two clock pulses after 1.2 mS. If this pulse is not there this signifies a logic 0. The ironic thing now is that although the ampli- tude of the pulses is constant during recording, when the tape is played back the volume setting is extremely critical. One possible explanation is that one small interference pulse can easily convert a logic 0 into a logic 1. On the other hand, a dro...