Post by Klaus Haber
I found some time to continue the discussion.
Post by Paul Post by Klaus Haber
I use the ASUS-Board P5GD2 Deluxe. This board has totaly 8 USB 2.0-ports, 4
at the real panel direct connected and 4 ports at the front, connected by
cable to the board.
I found out, that 2 ports at the front will not work properly, if I connect
them to my Epson Scanner. If I do so, I get a failure message, that an
other scanner is already connected to the computer, which is not true. All
other 6 USB-ports are working well with the scanner. I changed the
USB-cable, no success. If I connect a camera, an USB-stick, an external
USB-harddisk to these both ports, they all work well, exception is the
scanner. I have no idea, what could be reason of this effect. Have the
different USB-ports also differnt valances?
If I connect the scanner to the different ports of my laptop, also no
problems. So I assume, that the failure should be at the ASUS-board.
Is there one possibility to test generally an USB-port for its
Thank you for comments, regards
You have one of these in the motherboard box.
Correct, I have this adapter (missing the game plug).
Post by Paul
Disconnect the front panel USB wiring. Connect up the
2x5 USB cable of the 14-000012222 adapter. (You don't
need to connect the game port.)
Plug the scanner into the faceplate of the adapter.
Test the scanner. If it works with the Asus adapter,
but not with the computer wiring, then the computer
wiring is faulty.
Maybe I didn't report exactly enough.
This adapter was installed due to the handbook of the motherboard since I
got the computer. I used this adapter all the time with success for all
commen hardware. Only the scanner was connected from the beginning to the
rear USB-port. The reason was the local arrangement of the scanner at the
Some month ago I rearranged the local hardware and the scanner moved to a
place, from which it was easier to plug the USB-cable into the adapter at
the frontside than to the real. And since this rearrangement I got the
malfunction of the scanner. Therefor I don't believe, that the malfunction
is due to a failure in wiring or thomething else. If I connect the scanner
back to the realport, it is running well again. If I connect other
consumers (cameras, sticks, harddisks a.s.o.) to the same frontadapter,
they are also running well. That would demonstrate, that the wiring is ok.
An other point. As far as I know, there are two classes of USB-ports. I
don't mean the 1.x resp. 2.0 clas but the class of powersupply. One class
has a powercapacity of ~ 200 mA ( I don't know the exact value) and the
other class of ~ 500 mA (not the exact value). The first class is used by
hardware with low powerconsumption, the second one for high
powerconsumption. USB-hardware with high power will not run proper, if they
are connected to the lowpower USB-port. I took a look at ASUS Homepage, but
I did not found any information about the class of my ports at the
motherboard. My scanner has an own powersupply, so it should not be
necessary to use a lowpower-port.
At the other hand, the scanner will run at all 3 USB-ports at the laptop.
Grrrrrrrrrrrrrrrr, I don't understand this ;-)
I studied your link exactly and I found nothing which did not meet my
wiring. From this point of view, every thing is wired right.
Can you (both) give some comments to the powersupply-classes of the
USB-ports in connection with the plugged consumers?
As far as I know, the classes are 100mA and 500mA. All Asus motherboard
ports will be 500mA. There is a Polyfuse near each USB header, and it
is rated for more than 1 amp. The 1 amp is shared by the two USB ports.
So DC power should not be an issue. Each Asus port should meet the
high power spec.
The 100mA limit happens, when you use a bus powered hub connected to a
motherboard port. Like this.
500mA ----- 100mA
Motherboard_USB ------- bus_powered_hub ----- 100mA
The current limit still applies, even if the bus powered hub has only one
output port. An example of a one port hub, is a 5 meter USB active buffer cable.
Motherboard_USB ------- 5_meter_buffer_cable (one port hub) ----- 100mA
Bus_powered means all power is derived from the original 500mA
If the scanner works with the adapter I described (this one) -
but not with the computer case wiring, then the computer
case wiring is not working correctly. As a front panel
substitute, you can use a 5 1/4" drive bay USB panel
as a substitute. For cabling, what you want is a minimum
of loose wire. If the loose wires here were part of the
USB cable, the electrical performance might not be
very good. USB2 is a 400Mbit/sec signal, and the signal
should be maintained in a transmission line environment.
Single loose wires, with no ground reference, don't have
a precisely defined impedance, and signal reflections
To give an example of the problem, I have an Antec case
here, where the front USB port only runs at USB 1.1 speeds.
This is a known problem with the cable and PCB assembly that
Antec shipped with a number of their older computer
cases. Antec has improved the design, with their latest
stuff. I haven't heard of problems with the more recent