Controlling the Tape Drive

Software controls the Tape Drive by writing the mode (4 least significant bits) to drive's register C, as following:

  Mode    Operation
  ------------------
  00H     STOP
  01H     RWD
  02H     FF
  07H     READ
  0bH     WRITE
  0fH     Make GAP
  -------------------

The drive executes the associated operation immediately after receiving the mode and remains in that state until a new mode is written to C, or the operation finished by its own which occurs when the tape reaches its end; when that happens, the drive changes automatically to mode STOP and writes 00H to register C. Current mode can also change if the Operator intervene performing a manual operation.

Every time the content of C changes (for whatever reason) an interrupt is asserted to the to EXT-BUS so appropriate actions can be taken by software. Software can also read the register C at any time to learn about current Mode and Status of the drive.