PC(IV)                       10/15/73                      PC(IV)

     pc  -  PC-11 paper tape reader/punch

     Ppt  refers to the PC-11 paper tape reader or punch, depend-
     ing on whether it is read or written.

     When ppt is opened for writing, a  100-character  leader  is
     punched.   Thereafter  each  byte  written is punched on the
     tape.  No editing of the characters is performed.  When  the
     file is closed, a 100-character trailer is punched.

     When ppt is opened for reading, the process waits until tape
     is placed in the reader and the reader is on-line.  Then re-
     quests  to  read cause the characters read to be passed back
     to the program, again without any editing.  This means  that
     several  null  leader  characters will usually appear at the
     beginning of the file.  Likewise several nulls are likely to
     appear  at  the end.  End-of-file is generated when the tape
     runs out.

     Seek calls for this file are meaningless.


     If both the reader and the punch  are  open  simultaneously,
     the  trailer is sometimes not punched.  Sometimes the reader
     goes into a dead state in which it cannot be opened.

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