Universal Serial Bus: Difference between revisions

In designing USB 2.0, the USB-IF insisted on a single implementation. That single implementation is Intel's '''ExtendedEnhanced Host Controller Interface''' ('''EHCI'''). However, even though the USB 2.0 specification requires that a USB 2.0 interface support USB 1.0 devices, this doesn't mean that the EHCI must support USB 1.0 devices, and in fact, it doesn't. Each EHCI host controller is accompanied by (usually several) UHCI and/or OHCI host controllers. When a USB 1.0 device is attached, the EHCI simply hands control over to a '''companion controller'''. Refer to figure 1 for a simple block diagram implementation of this behavior. Therefore, the system programmer must support all three standards in order to support USB 2.0.