26.16.2 Connect Instances Using Existing Ports
In order to connect two module instances using existing ports, you must specify the output port (the signal source) and the input port (the signal destination). New ports will be created across the design hierarchy as needed, in order to propagate the signal.
Select Top button and pick one of the available design tops.
Show/Hide Ports button to see the ports of the selected instance, if needed.
Select an instance using left click and a port using right click
Connect Output Port.
The output instance and port are presented in the Refactoring Connect View
Select another instance using left click and a port using right click
Connect Input Port.
The input instance and port are presented in the Refactoring Connect View
Input textbox along the previous set instance and port:
The rest of the steps are the same as connecting instances using new ports. More details
Note : The swap between output instance and input instance doesn't work for directional ports (input or output).