did_it.i4.v = btvm(row.i4.r, column.i4.r, text.i1a.r,
			   num_chars.i4.r [,color.i4.r])

	did_it.i4.v = btvm_c(row.i4.v, column.i4.v, text.i1a.r,
			     num_chars.i4.v [,color.i4.v])

	This routine will display background text if "num_chars" is greater
	than or equal to zero.  It will read in background text if "num_chars"
	is less than zero.  This routine is a replacement for 'tvm(_c)' for
	applications utilizing window management.

	row, column	starting screen coordinate location
	text		user buffer of ASCII data to be read or written,
			one character per byte
	num_chars	number of ASCII characters to be read from or
			written to the screen.  If the value of "num_chars"
			is negative, a read operation is performed.
			(Note : A null string will be returned if the
			 window is occluded.)  If "num_chars" is positive,
			a write operation is performed.  If "num_chars" = 0,
			the length of the string pointed to by "text" is
			determined and used.
	[color]		display color  (If a background color other than
			black is desired, a compound color value can be
			constructed using tv_colors or TV_COLORS_WBLINK.)
			(default is WHITE)
			(constants are in 'cnsparam')

	This function returns status values as follows:

	TRUE			window I/O actually done
	FALSE			no window I/O done

	This function requires the following include files:

	cnsparam_h, cbslib_h

	Related functions:

	window_tvm(_c), window_tvmx(_c), tv_colors, TV_COLORS_WBLINK,

	C/C++ usage:

	static const char	text[] = "Text";
	int	did_it;
	int	row = 2;
	int	column = 1;
	int	num_chars = 0;
	int	color = WHITE;

	did_it = btvm_c(row,column,text,num_chars,color);