Lian Li PC-65 and USB 2.0

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Lian Li PC-65 and USB 2.0

Postby Joe_Hallock » Tue May 14, 2002 11:39 am

I purchased a Lian Li PC-65 case which has 4 USB ports located on the bottom of the front side. My question is this, do these ports support USB 2.0? Thank you for any help,

-Joe
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Postby Reader » Tue May 14, 2002 5:03 pm

USB is both backward and forward compatible.

You can plug a 2.0 device into a 1.0 system. It just won't go as fast.

If you plug a 1.0 device into a 2.0 system, it will also work.

While I'm currently looking through a 6MB PDF file to find out the EXACT answer to your question, I'm learning that there are new techniques being used in the cabling process that could affect overall performance.

The Lian-Li cases basically use straight wires to connect the USB sockets to the pins on the motherboard/adaptor card. The High Speed USB 2.0 specifications are clearly insisting on tightly twisted cables with a special grounding technique on both ends. (Nothing said so far about "in the middle!") Just to give you a small idea of why I can't answer your question, here are a few pertinent lines from the document:

====begin text=========
(Note: the "?" are really the scientific symbol for Ohms -- Omega)

Figure 7-1 depicts an example implementation which largely utilizes USB 1.1 transceiver elements and adds the new elements required for high-speed operation.

High-speed operation supports signaling at 480 Mb/s. To achieve reliable signaling at this rate, the cable is terminated at each end with a resistance from each wire to ground. The value of this resistance (on each wire) is
nominally set to 1/2 the specified differential impedance of the cable, or 45 ?. This presents a differential termination of 90 ?.

For a link operating in high-speed mode, the high-speed idle state occurs when the transceivers at both ends of the cable present high-speed terminations to ground, and when neither transceiver drives signaling current into the D+ or D- lines. This state is achieved by using the low-/full-speed driver to assert a single ended zero, and to
closely control the combined total of the intrinsic driver output impedance and the RS resistance (to 45 ?, nominal).

====End of Text=====

Well, I guess you can figure out why I can't answer your question!

But being realistic, the Lian-Li connectors may degrade the performance but still allow it. The question is whether they will degrade it to the point a 2.0 device on the other end is recognized as only a 1.0 device and the low-speed performance is all that's delivered.

The same 4 conductors are used by both 1.x and 2.0 USB...but 2.0 adds the element of shielding the cable and twisting the cable.

The plugs should still work. It's the wiring between those plugs and the transceiver on the Motherboard or Adaptor card that determine whether we'll need some kind of "fix" to get full performance.

I think.

Cheers,
reader
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Postby Rraven » Tue May 14, 2002 5:51 pm

I may be mistaken on this but it sounds very much like the differences between the old 422 /485 types of communication on wired networks, the termination resistance being where you can gain added speed, if this is so one could take an exsisting USB1.1 and with a bit of soldering make it a full USB2.0 compatable. The twisted pair is another item that kind of gives this away to me...Anyone with other thoughts....Atang?...



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Postby Joe_Hallock » Wed May 15, 2002 9:39 am

Reader wrote:USB is both backward and forward compatible.

You can plug a 2.0 device into a 1.0 system. It just won't go as fast.

If you plug a 1.0 device into a 2.0 system, it will also work.

While I'm currently looking through a 6MB PDF file to find out the EXACT answer to your question, I'm learning that there are new techniques being used in the cabling process that could affect overall performance.

The Lian-Li cases basically use straight wires to connect the USB sockets to the pins on the motherboard/adaptor card. The High Speed USB 2.0 specifications are clearly insisting on tightly twisted cables with a special grounding technique on both ends. (Nothing said so far about "in the middle!") Just to give you a small idea of why I can't answer your question, here are a few pertinent lines from the document:

====begin text=========
(Note: the "?" are really the scientific symbol for Ohms -- Omega)

Figure 7-1 depicts an example implementation which largely utilizes USB 1.1 transceiver elements and adds the new elements required for high-speed operation.

High-speed operation supports signaling at 480 Mb/s. To achieve reliable signaling at this rate, the cable is terminated at each end with a resistance from each wire to ground. The value of this resistance (on each wire) is
nominally set to 1/2 the specified differential impedance of the cable, or 45 ?. This presents a differential termination of 90 ?.

For a link operating in high-speed mode, the high-speed idle state occurs when the transceivers at both ends of the cable present high-speed terminations to ground, and when neither transceiver drives signaling current into the D+ or D- lines. This state is achieved by using the low-/full-speed driver to assert a single ended zero, and to
closely control the combined total of the intrinsic driver output impedance and the RS resistance (to 45 ?, nominal).

====End of Text=====

Well, I guess you can figure out why I can't answer your question!

But being realistic, the Lian-Li connectors may degrade the performance but still allow it. The question is whether they will degrade it to the point a 2.0 device on the other end is recognized as only a 1.0 device and the low-speed performance is all that's delivered.

The same 4 conductors are used by both 1.x and 2.0 USB...but 2.0 adds the element of shielding the cable and twisting the cable.

The plugs should still work. It's the wiring between those plugs and the transceiver on the Motherboard or Adaptor card that determine whether we'll need some kind of "fix" to get full performance.

I think.

Cheers,




Thanks a lot for all your help,

Joe H.
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Expert Advice: Just try it!

Postby Reader » Thu May 16, 2002 4:01 am

Many of us purchased PC cases that include USB ports on the front of the case.

This thread posed the intelligent question: will those connectors support USB 2.0 devices?

I contacted MacPower, just one of many firms developing USB 2.0 device enclosures to get their opinion. Here is a summary:

1. The best way to find out is to "just try it!" If it doesn't work well, proceed to the following 2 points.

2. Twist the cables yourself; this will reduce the noise a little bit.

3. Another thing which influences the performance is the length of the wire. Shorter is better.

So, we users end up in a "grey zone" where performance of 2.0 devices is not assured. But barring a fix coming from the case manufacturers, it's probably as good as it's going to get.
reader
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