gnupic@linuxhacker.org

Mark Gross wrote:
>>
>>Also, these chips are low-speed, which makes them even slower than
>>serial once you subtract out the protocol overhead. Granted, you do get
>>some nice error detection and insertion/removal events from the  USB
>>stack, but what's hidden in the fine print is that low-speed HID
>>devices (the easiest to interface to under Windows) get only 800
>>bytes/sec per HID report ID. I say "low-speed" and not "1.5 Mbps"
>>because 1.5 Mbps is only the signaling rate, and only a small portion
>>of the available bandwidth is allocated to low-speed devices.

Is that true even if you have a USB bus with only low speed devices on it? It is frequently
possible to arrange that. PCs typically have multiple USB ports, and in at least some
of them, each port is on a separate bus. And if you're designing some sort of dedicated
thing, you can just keep other USB devices out of the picture.

Still, your point is valid: the usefulness of the 16C765 is rather limited by the fact
that it only does low speed; that pretty much restricts it to low data rate devices
like keyboards and mice. The USB-enabled members of the 18F family seem to have disappeared
from the Microchip web site (they're not listed either in the web pages summarizing
the 18F series, or in the PDF file of future products), so it's not clear whether they
will ever see the light of day - perhaps there just wasn't enough demand from Microchip's
customers for them.