For example, connect two AV4PRO switches together, where the USB from the Master of port 1 is connected to the console port of the Slave.  The keyboard and mouse are connected to the master AV4PRO.

AV4PRO Master Slave  

Hold down the CTRL key (default) and press 1 to chose port one of master, press a press 2 then release the CTRL key.  This will instruct the AV4PRO to switch to port 1 on the master and then to port 2 on the slave.