IO (CASSETTE ACESS)                                  PAGE I12
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          CASSETTE INPUT/OUTPUT/VERIFY INSTUCTION
 
          Format         CALL IO(type,length,vdp-address[,...])
 
           The three different cassette I/O instructions use the same
          format. The write and read instructions physically perform
          Input/Output to the cassette. The verify instruction will
          read a tape and compare it, byte by byte, against what is in
          the specified VDP area. All will report an  I/O error if one
          is detected. No prompts are present with these three formats.   
          These three types control the cassette directly so no prompt 
          will tell the user to turn on or off the cassette record/play 
          buttons. The programmer must inform the user with own prompt.
 
          Programs
          (Presently I have no cassette to write programs with.)
 
          AUDIO GATE
          ----------
          CRU bit 24 is the audio gate which allows data being read to
          be heard. If the bit is set to 1, the data being read is
          heard, and if the bit is set to 0, the data is not heard.
          Setting the bit to a 0 or 1 is done with an IO instruction, or
          a Assembly instruction.
 
          MOTOR CONTROL
          -------------
          There are two CRU bits (22 and 23) used to control cassettes
          1 and 2, respectively. When there is no Cassette IO being
          done, both motors remain on. When Cassette IO is specified,
          the DSR (Device Service Routine) will control the data being
          read. If there are two motor units connected, the data will be
          read simultaneously, or you may have the option of reading
          data from one motor unit and playing the recorded voice from
          another motor unit through the TV (Monitor) speaker. 
          
          *NOTE:
          Compatibility with or without 32K or other devices is not a
          concern as IO needs no RAM to work with. Therefore from just
          a console all IO commands will work fine. If you only have a
          Cassette and RXB you can quickly load/save/verify without
          menus, or just make up your own.