"Jimbo" said:
Paul,
On a P4P800E-Deluxe mb, There are 4 USB ports on the rear panel and 4
internal USB header ports.
What are the front panel USB ports you referred to?
I use the 4 rear ports. Should I avoid hot plugging anything on these ports?
Or would it be better to stop using those ports and switch over to the 4
internal header ports?
Jimbo
There are a couple of ways to look at this issue:
1) The ICH4, ICH5, ICH5R are weaker than ordinary USB devices.
They are falling over, when every other USB device we know
about is not.
2) The problem is aggravated by the way the USB port is wired.
The ports that use connectors on the motherboard, like the
ones on the back of your computer, are safer. The reason is,
Asus has grounded the shield on those USB connectors.
When you connect to a rear USB port, static electricity on the
USB cable you are plugging in, will be drained to the shield
on the Asus USB connector. There are also the spring clips that
touch the I/O ports - they could help drain static discharge
to the computer case metal and from there to ground on the
PSU case.
The shield ground on the motherboard connectors _should_ reduce
the frequency of occurrence. But, there are no guarantees.
If you want a guarantee, buy a cheap USB2 card and use the
interfaces on it. Then, the Southbridge cannot be destroyed.
3) Now we come to the USB headers on the motherboard. If you
use Asus adapter plates, with the nice USB cables on them,
you should be as safe as with the shields on the motherboard
USB connectors. The same would be true if you use an Asus
J-panel for a drive bay USB interface.
The problem is with computer case (front panel) USB connector
solutions. Many computer cases come with nice wire assemblies,
but they will have three ground wires. The Asus USB header
has two ground wires. If the third ground wire on the
computer case is left floating, then the shield of the USB
connector has no where to drain a static discharge.
If you are using only one of the two USB headers on the
motherboard, that means you have four ground pins at your
disposal. You can use a ground pin from a second header, to
connect the third (shield) ground connection on the computer
case cable assembly.
Another way to get a shield ground connection, is to find a
screw that makes good electrical contact with the computer
case metal. Arrange to fasten a stiff wire to the case. The
diameter of the stiff wire must be small enough to enter the
square connector of the GND wire. That grounds the shield to
the computer case.
One source of nice wires, is 1/4 watt or 1/8 watt
resistors (available at Radio Shack). The legs on some
resistors are a perfect fit into the opening on the GND
wire.
----- leg from a ________ USB shield GND wire
/ | \_________________ | GND |_____________
--+-- resistor snipped |________| from comp. case.
| to correct length
^
|
\_____ screw grounded to computer case metal. A
shiny metal to metal contact, not resting on
any paint.
The toughest part of this little project, is determining which
wire goes to the shield of the connector. I doubt the three
ground wires will be marked, as to which two of them are signal
ground wires, and which one is the shield ground wire. Only the
shield ground wire should be connected to a "gimmick" ground
like this one made from a piece of wire and a ground screw on
the case.
If in doubt about any of this, I still think a separate USB card
is a much better solution. When the mobo warranty has expired at
the end of three years, you would definitely want a USB2 card at
that time. Buying a USB2 card now, simply avoids the nuisance of
having to return the motherboard and wait three weeks to get
another one.
All integrated chips have an ESD rating (human body model).
And a latchup current rating. Sometimes chip companies do a
great job of protecting a chip against static electricity and
sometimes they do not. A good chip may have 2 kilovolt ESD rating,
and from 500mA to 1A latchup current rating. The best chip I
know of, a Maxim RS232 interface chip, has a 15 kilovolt ESD
rating. Chip companies do strive to make the best level of
protection they can, because it improves the quality of the
components they ship (no duds reach the factory floor at the
motherboard maker, due to static killing them). I doubt Intel
made the chips this way on purpose, as there are design rules
that the chip designers are supposed to adhere to, when designing
the chips. This fault will undoubtedly come as a surprise to
Intel engineers, an unwelcome surprise.
It is possible to add protection devices to the outside of
a chip, to mitigate the effects of static electricity. The
problem with that kind of solution, is at high frequencies
(like the 400Megabit/sec rate of USB2), very few protection
devices are good enough to connect to a high speed signal
without corrupting the data content. Here is an example
of a device suitable for protecting a USB 1.1 (12Megabit/sec)
port - if used on a USB2 port, it would likely crush the
signal.
http://www.semtech.com/pdf/stf202.pdf
or try here
http://web.archive.org/web/20041113061336/http://www.semtech.com/pdf/stf202.pdf
To retrofit a device like this to a motherboard would be
very tricky. Especially as the USB signals run at such
high speeds, and don't like to have unbalanced stubs connected
to them.
HTH,
Paul
