HP OpenVMS Systems

Using sys$qiow and terminator masks?

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The Question is:

 
After using the appropriate search criteria I did not find an entry for my
 question.  I apologize if this question has been asked.  I need to talk to
 RS232 devices and I inherited a piece of code that uses QIOW to communicate
 over the RS232 line.  QIOW us
es a terminal mask to define the terminator, the code is looking for.  I've
 read the section of the VMS manual with regard to this mask (ie. "function
 terminators" in Terminal Driver  chapter  of I/O  User's:   Part  I) and I
 still don't get it.  Could yo
u help me understand how it works.  Maybe an example or to to go with it?
 
Thanks,
 
Jeff
 
 

The Answer is :

 
  When one of the terminator characters specified in the mask is
  seen in the input stream, the sys$qiow read operation completes,
  and the AST (if specified) fires.
 
  Probably the most commonly-used terminator in serial communications
  is the carriage return character.
 
  Attached is a BASIC example of the sys$qiow call specifying the
  terminator mask.
 
 
 1      OPTION TYPE = EXPLICIT
        ON ERROR GO TO OOPS
        EXTERNAL LONG FUNCTION  SYS$ASSIGN, SYS$QIOW
        EXTERNAL LONG CONSTANT  IO$_READVBLK, IO$M_TIMED
        DECLARE LONG THE_LENGTH, TT_CHAN, S, I
        DECLARE LONG CONSTANT   BACKSPACE_BIT=256, TAB_BIT=512,         &
                                LINEFEED_BIT=1024, RETURN_BIT=8192
        MAP (IO_STAT)   WORD    IO_STAT, TERM_OFF,                      &
                        BYTE    TERM_CHAR, FILL, TERM_LEN, CURS_POS,    &
                        LONG    TERMINATOR_MASK, TERMINATOR_BITS,       &
                        STRING  THE_BUFFER = 80
 
        TERMINATOR_BITS = BACKSPACE_BIT + TAB_BIT + LINEFEED_BIT + RETURN_BIT
 
        S=SYS$ASSIGN ("TT", TT_CHAN,,)  !Get a channel for the QIO
        WHILE 1 + 1 = 2
                  S=SYS$QIOW (  ,TT_CHAN BY VALUE
                        ,IO$_READVBLK + IO$M_TIMED BY VALUE             &
                        ,IO_STAT BY REF                                 &
                        ,,,THE_BUFFER BY REF, LEN(THE_BUFFER) BY VALUE  &
                        ,10% by value ,TERMINATOR_MASK BY REF           &
                        ,,)
 
          PRINT S; "IO_STAT"; IO_STAT;          &
                "TERM_OFF"; TERM_OFF; "TERM_CHAR"; TERM_CHAR;   &
                "TERM_LEN"; TERM_LEN; "CURS_POS"; CURS_POS
          PRINT "Buffer="; THE_BUFFER; "                ";
          PRINT " "; ASCII(SEG$(THE_BUFFER,I,I)); FOR I = 1 TO 20
          INPUT THE_BUFFER                      !Exit with control-Z here
        NEXT
 OOPS:
        PRINT ERT$(ERR) UNLESS ERR=11
        RESUME 2
 2      END
 

  

     

     
answer written or last revised on ( 24-MAR-2000 )
     
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