If the port selected on the row is a top-level port with a direction IN or an instance port with direction OUT, all ports of direction IN and INOUT on the instances are compatible with it.
If the port selected on the row is a top-level port with direction OUT or instance port with direction IN or INOUT, all ports with direction IN are compatible with it.
Bus ports or slices are only compatible with bus ports or slices of equal size.
If there are no compatible connections between a port in the row area and an instance in the column area, the cell is shaded and unavailable.
The pull-down menu in the cells only lists compatible ports.
