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TB(4)											    TB(4)

       tb - line discipline for digitizing devices

	    NTB  1    # RS232 interface for Genisco/Hitachi tablets

       This  line  discipline provides a polled interface to many common digitizing devices which
       are connected to a host through a serial line.  When these devices  stream  data  at  high
       speed, the use of the line discipline is critical in minimizing the number of samples that
       would otherwise be lost due to buffer exhaustion in the tty(4) handler.

       The line discipline is enabled by a sequence:

	    #include <sys/tablet.h>
	    int ldisc = TBLDISC, fildes; ...
	    ioctl(fildes, TIOCSETD, &ldisc);

       A typical application program then polls the digitizing device by reading  a  binary  data
       structure  which contains: the current X and Y positions (in the device coordinate space),
       up-down status of the buttons or pen stylus, proximity information (when available), and a
       count  of  the  number  of samples received from the input device since it was opened.  In
       addition, devices such as the GTCO append tilt and pressure information to the end of  the
       aforementioned structure.  For the Polhemus 3-D digitizer the structure read is completely
       different. Refer to the include file for a complete description.

       While in tablet mode, normal teletype input and output functions take place.  Thus, if  an
       8  bit  output data path is desired, it is necessary to prepare the output line by putting
       it into RAW mode using ioctl(2).  This must be done before changing  the  discipline  with
       TIOCSETD, as most ioctl(2) calls are disabled while in tablet line-discipline mode.

       The  line  discipline  supports	ioctl(2)  requests  to get/set the operating mode, and to
       get/set the tablet type and operating mode by or-ing the two values together.

       The line discipline supports digitizing devices which are compatible with  Hitachi,  GTCO,
       or Polhemus protocol formats.  For Hitachi there are several formats with that used in the
       newer model HDG-1111B the most common.



3rd Berkeley Distribution		  August 1, 1987				    TB(4)
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