AQ ECU allows connecting to one or more ESCs at the same time. The number connected ESCs is limited only by how many USB ports (and serial adapters for ESC32 v2) are available. This is especially convenient with the ESC32 v3 on-board USB interface. For example one could connect to all ESCs on a quad at the same time to quickly upload or compare settings, update firmware, etc.
Note for ESC32 v3 USB connections: The “STM virtual” serial (COM) port will not show up in the list of available ports until the ESC is physically plugged in and the USB driver is loaded (usually signaled by the operating system with an audio and/or visual indicator). Wait for the driver to load before selecting the port or trying to connect. If the USB link is later removed, the port will become marked as “INVALID” in the ports selector list (but will not disappear). Always try to disconnect the link manually (using the Disconnect button) before removing the USB cable, otherwise you may experience errors.