TB(4)		    UNIX Programmer's Manual		    TB(4)



NAME
     tb - line discipline for digitizing devices

SYNOPSIS
     /sys/conf/SYSTEM:
	  NTB  _1    # RS232 interface for Genisco/Hitachi tablets

DESCRIPTION
     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 _t_t_y(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 dev-
     ice 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 pres-
     sure information to the end of the aforementioned structure.
     For the Polhemus 3-D digitizer the structure read is com-
     pletely different. Refer to the include file for a complete
     description.

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

     The line discipline supports _i_o_c_t_l(2) requests to get/set
     the operating mode, and to get/set the tablet type and
     operating mode by _o_r-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.

SEE ALSO
     tty(4)



Printed 11/26/99	 August 1, 1987                         1






TB(4)		    UNIX Programmer's Manual		    TB(4)



DIAGNOSTICS
     None.





















































Printed 11/26/99	 August 1, 1987                         2