# Understanding USB Descriptors speed

I have several USB devices that are capable of running High Speed 2.0 (480 Mbps) mode but runs Full Speed 1.1 (12 Mbps) instead.

Take for example a USB DAC:

It advertise USB 2.0 compliant and fall back capability to 1.1

 SupportedUsbProtocols    : 0x03
Usb110                  : 1 (yes)
Usb200                  : 1 (yes)
Usb300                  : 0 (no)


But in the device descriptor:

bcdUSB                   : 0x110 (USB Version 1.10)


Means that the manufacturer is using a IC capable of 2.0 but configured to run at 1.1?

This is not an issue but I was wondering what is the goal to run a device capable of running High Speed at lower speed. This create the need of a transaction translator and reduce overall performance.

• It means your board layout is easier, because 1.1 speeds are pretty insensitive to trace impedance. Jul 22, 2020 at 19:11
• For many years already, virtually all USB devices have implemented at least USB 2.0 protocol. This does not imply that they implement USB High Speed as it's optional in USB 2.0. They still profit from other USB 2.0 advances.
– Codo
Jul 22, 2020 at 20:21
• @Codo makes sense post this as an answer please. Jul 22, 2020 at 23:35