USB EHCI, compatibility with low speed and full speed devices
Almost all USB 2.0 hosts support both low and full speed. The EHCI interface specification. 


  The EHCI driver provided high-speed functions for USB ports on the motherboard or on the NEC based card. In more recent hardware, all ports are routed through an internal "rate-matching" hub (RMH) and the EHCI controller indirectly provides full and low speed USB functions.


http://en.wikipedia.org/wiki/Host_controller_interface_(USB,_Firewire)

You can take a look at the specification on Intel's web site:

http://www.intel.com/content/www/us/en/io/universal-serial-bus/ehci-specification-for-usb.html