SLYY228 November 2024
USB4 is significantly different than previous USB generations. In a USB-C system, a USB2 or USB3.2 product operates without the need for USB Power Delivery (PD). For example, if you plug in a USB2 thumb drive into a non-USB PD-enabled USB-C port, you will be able to use the drive just like you could if the drive was plugged into a USB Type-A receptacle.
Taking advantage of all of the capabilities of a USB4 product requires USB PD. During the discovery process, if both port partners and as well as the cable support USB4, then the downstream-facing port (DFP) issues the USB PD Enter_USB message to the cable and port partner. If a USB4 product is inserted into a USB-C port that doesn’t support USB PD, then the USB4 product operates in a legacy USB mode (either USB2 or USB3.2).