Re: USB ports issues
- From: "M.I.5¾" <no.one@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 10 Dec 2007 11:26:40 -0000
"leoliver" <leoliver@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:16084A3C-17CA-4CD7-9BE1-5A0917CB3671@xxxxxxxxxxxxxxxx
Hi Everybody,
Device Manager tells me I have more USB root hubs than I can see on my
computer. It says there are 4-hubs, 3 of which have 2 ports available, and
one of which has 6 ports available. The 6-port hub is supposed to be a
high
speed port.
My computer only has 6 USB plug in's, which confuses me. Wouldn't there
be
a plug in for each port ?
Also, I had a external HD connected to a USB plug in, and I kept getting
warning messages that the USB port I was using was a medium speed, not a
high
speed port. But I couldn't tell the difference because between ports.
The warning messages said that the 6-port plug in was high speed so I
moved
the external HD to another port, and I got lucky because now device
manager
says that the HD is plugged in to the 6-port , high speed hub.
Why does a 6-port hub have only 2 plug in's ? And other than guessing, how
do you tell which ports are high speed? My computer handbook only shows
the
location of the USB plug ins, and doesn't tell me which are high speed.
Feedback will be appreciated !
your friend,
Larry
Your device manager is telling you like it is.
On motherboards that support USB2, there are in fact 2 sets of host ports
with their associated root hubs. The first, generally with 2 ports per root
hub support the 1.5 Mbps and 12 Mbps USB standards (the old USB1 spec or
OHCI ports). When the high speed (480 Mbps or USB2 or EHCI ports) was
implemented, there was a problem. The method of terminating the USB1 ports
wouldn't work at the USB2 speeds. Thus another host port with an associated
root hub was added (usually one root hub handles all the USB ports - in your
case 6 of them).
You should find that the total ports on all your root hubs is double the
number of physical ports (which I believe you have).
When you connect an older USB1 peripheral, it is connected via the low speed
root hub to one of the OHCI host ports and away it goes.
When you connect a newer USB2 peripheral, it too is connected via the low
speed root hub to one of the OHCI host ports. However, this time, during
the initial houskeeping interchange, the USB host system identifies the
device as a high speed device and instructs it to switch into high speed
mode. At the same time, it reroutes the connection from the low speed root
hub to the high speed root hub (and hence to the EHCI) wherupon high speed
communication can start.
However, once high speed communication starts, if the received data is not
substantially error free (possibly because the cable is not up to the job,
is too long or even that part of the peripheral's port is damaged), then the
host system will default back to the USB1 OHCI port and present you with an
error message telling you that your peripheral is connected to a USB1 port
and should be connected to a USB2. The error message is a catch all and in
the true tradition of error messages doesn't always tell you exactly what is
wrong. Front panel USB ports often give this error because they are
frequently wired using cheap ribbon cable which will never carry USB2
signals.
-Executive Summary-
The answer to your question is: that you have 6 physical ports, and
internally your motherboard has 6 low speed ports and 6 high speed ports.
The system automagically connects your physical port to the correct root hub
for the speed of communication required. thus you can connect 6 USB1
peripherals or 6 USB2 peripherals or any other combination up to 6. Your
high speed communication is failing because something in the wiring is not
up to the job of carrying a 480 Mbps data stream.
.
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