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Propagation delay

Full-/high Speed: ≦26ns/cable

 Low speed: 18ns /cable

大家見過此標(biāo)準(zhǔn)的分類嗎

非常感謝

我查到了

我有點(diǎn)不理解

為什么Low speed: 18ns /cable反而比Full-/high Speed: ≦26ns/cable要求的還要嚴(yán)格呢

這點(diǎn)我也比較困惑

其它哪位大俠可以幫忙解惑

甚是感謝！

roger呢？

哪位大蝦幫幫忙吧

急呀

客人急需我的回復(fù)

我自己卻一頭霧水

怎么交得了差啊

先謝了！

標(biāo)準(zhǔn)啊。

HDMI不也有這樣的現(xiàn)象嗎？

HDMI標(biāo)準(zhǔn)中的哪個(gè)現(xiàn)象與此類似

樓上的朋友能不能解釋的更清楚點(diǎn)呢

謝謝！

誰能幫忙解釋一下啊

各路高手不可能都不知道吧

希望不吝賜教

此問題始終懸而未解

再次期待中......

還是李小龍大俠熱心腸

多謝

嗯,full-speed是USB1.1的高速模式，high-speed 是USB2.0模式,full-speed并非全速的意思，它是相對high-speed而言的，實(shí)際速度為12Mbps，與USB1.1完全一樣，所謂得full-speed其實(shí)就是USB2.0對USB1.1的兼容模式，USB2.0 （full speed）不等于USB2.0 full speed，它真正得含義是USB2.0工作在USB1.1 full speed模式下。

會不會是full speed模式其實(shí)是USB1.1標(biāo)準(zhǔn)里面,所以會要求沒Low speed的嚴(yán)格?我這樣理解的,不知對不對?

［卓一航 在 2009-7-6 17:57:22 編輯過］

［卓一航 在 2009-7-6 17:58:11 編輯過］

USB傳輸速率劃分為

LOW SPEED

FULL SPEED

HIGH SPEED

SUPER SPEED

照常理解，都應(yīng)該是速度的提升，各特性參數(shù)應(yīng)該會更嚴(yán)格

我唯一的想法

覺得可能是由于當(dāng)時(shí)PC端電子設(shè)備技術(shù)的局限性

為能達(dá)到USB的設(shè)計(jì)傳輸速率

從而限制整個(gè)線材的用線長度

故將Delay值規(guī)定較小

嗯,也只能這樣解釋.....,或許以后USB協(xié)會芯片更先進(jìn)了,以后的延時(shí)要求越來越松,線材使用也可以越來越長了.

colthuang:

嗯,也只能這樣解釋.....,或許以后USB協(xié)會芯片更先進(jìn)了,以后的延時(shí)要求越來越松,線材使用也可以越來越長了.

這也只是我的個(gè)人推理

我也不知道這樣是不是合理的解釋

我想應(yīng)該有更合理的邏輯

aou83:

Delay is measured from the Series A connector pins to the Series B connector pins and is no more than 26 ns. For other cables, the delay is measured from the series A connector to the point where the cable is connected to the device. The cable delay must also be less than 5.2 ns per meter.

請問這里的5.2 ns per meter，為什么定義這個(gè)5.2ns/m值？和介電常數(shù)有關(guān)系嗎？

chiiwa:

請問這里的5.2 ns per meter，為什么定義這個(gè)5.2ns/m值？和介電常數(shù)有關(guān)系嗎？

我也不清楚，是規(guī)格定下的

There are two types of cables: 

1. Low-speed cables
2. Full and High-speed cables 

All low-speed devices must use a “captive” cable assembly as defined in Section 6.4.3 of the USB 2.0 Specification.  Common examples of low-speed devices are keyboards, mice and joysticks.  This requirement forces the cable to be specific to the device.  In other words, a low-speed device will have its own specific custom cable. 

Full-speed devices and high-speed devices use the same cable, called a standard detachable cable assembly.  Please see Section 6.4.1 of the USB 2.0 Specification.  The standard detachable cable assembly can be used by any full-speed or high-speed device that uses a USB B-receptacle.  Standard detachable cable assemblies can be purchased at stores.  

Full-speed and high-speed devices can have a captive cable.  There is no differences, electrically, between standard detachable cable assemblies and a captive cable of a full-speed or high-speed device.  A common example of full-speed and high-speed devices that use captive cables are webcams (web cameras). 

To reduce consumer confusion on cables, only full-/high-speed detachable cables are permitted.  Low speed devices are not allowed to use standard detachable cables.  Instead, they must have a permanently attached cable or use a custom connector. 

Section 7.1.1.2 of the USB 2.0 Specification explains why low-speed captive cables have to be shorter.  The capacitive load of long low-speed cables differs significantly from full- and high-speed cables.  This causes large signal reflections in the cables of low-speed devices.  The shorter cable minimizes the reflections.

樓上的意思是low speed 的delay比high speed嚴(yán)是因爲(wèi)長度比較短嗎？