On Mon, 30 Jul 2007, Dave Higton wrote:
> > According to the spec, every USB 2.0 device is
> > required to be compatible with a USB 1.1 host. It isn't required to
> > provide full functionality --
>
> Do you have a "chapter and verse" reference for this? I stated
> it to someone on a newsgroup recently; he then challenged me to
> provide a reference. I skimmed and searched the USB 2.0 spec
> but failed.
Here's one sentence in section 7.1:
An upstream facing high-speed capable transceiver must not
operate in low-speed signaling mode, but must be able to
operate in full-speed signaling mode.
More to the point is this sentence in 9.2.6.6:
A device capable of operation at high-speed can operate in
either full- or high-speed.
That's not exactly the same as being compatible with a USB 1.1 host;
the rest of it follows from the fact that the 2.0 spec is backward
compatible with the 1.1 spec.
Alan Stern
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