menu_update(_c)

	item.i4.v = menu_update(menu_id.i2.r, type.i4.r)

	item.i4.v = menu_update_c(menu_id.i2.v, type.i4.v)

	This routine will service a fixed menu on the TV screen which
	was created by an earlier call to menu_create(_c).  If this is
	called with "type" = MENU_UPDATE_TYP, the menu item which the cursor
	is under is highlighted with a white background.  If this is
	called with "type" = MENU_SERVICE_TYP, the item number interrupted on
	(if any) is returned.  It will also execute the service function
	(if any) associated with that field by menu_create(_c).  It will
	return a value of zero if the most recent interrupt didn't occur
	in any of the menu fields.

	menu_id		menu ID (returned by a prior call to menu_create(_c))
			(a value of MENU_TOP will result in servicing the
			 most recently created menu)
	type		function desired
			(MENU_UPDATE_TYP -> highlight/periodic,
			 MENU_SERVICE_TYP -> service keyboard)

	This function returns status values as follows:

	OK			success on MENU_UPDATE_TYP
	CBS_NO_SUCH		couldn't find the requested menu
	CBS_WINDOW_OCCLUDED	the requested menu is occluded
	CBS_NOTENB		user clicked on a disabled item
	otherwise		return selected item number or zero
				if no item was selected

	This function requires the following include files:

	cbslib_h, acnet_errors_h

	Related functions:

	menu_create(_c), multicolor_menu_create_c, menu_delete(_c),
	menu_topmost, menu_change_entry_c, menu_change_entry_case_c,
	menu_set_current_entry_c

	C/C++ usage:

	short	menu_id;
	int	item;
	int	type = MENU_SERVICE_TYP;

	item = menu_update_c(menu_id,type);