USB routing problems : D+/- length issues

Question

Hello everyone

I'm a user of Eagle for 2 years now, and i'm trying to make USB with an Overo and a dsPIC.

The thing is that I had read somewhere (http://www.usb.org/developers/docs/hs_usb_pdg_r1_0.pdf) that the signals D+ and D- must have the same length (they talk about non parallelism page 10 figure 5)

But here is the point : how you do that on Eagle , to force 2 wire to have the same length (or being parallel all the way), in autorouter mode of course but even in manual mode.

Thanks for the help .

Best Regards

Former Member · Answer

Vincent Vittori schrieb:

I'm a user of Eagle for 2 years now, and i'm trying to make USB with
an Overo and a dsPIC. The thing is that I had read somewhere
(http://www.usb.org/developers/docs/hs_usb_pdg_r1_0.pdf) that the
signals D+ and D- must have the same length (they talk about non
parallelism page 10 figure 5)

But here is the point : how you do that on Eagle , to force 2 wire to
have the same length (or being parallel all the way), in autorouter
mode of course but even in manual mode.

First of all, I would never use the autorouter for this. (I don't use it

at all... but here it's essential.)

Then, simply (manually) route your tracks as parallel as possible. You

can check their length with an ULP and correct them if necessary.

In EAGLE, there is no way to /force/ an equally long differential pair

during routing, neither manually nor by autorouter. Maybe V6 will add

something new here, but I don't know.

Tilmann

kcadsoft · Answer

On 09/23/11 08:08, Tilmann Reh wrote:

...
In EAGLE, there is no way to /force/ an equally long differential pair
during routing, neither manually nor by autorouter. Maybe V6 will add
something new here, but I don't know.

In V6 the (manual) ROUTE command will treat signals that have the

same net class and the same name (one ending with '+' and the other

with '-') as "differential pairs". When picking up one airwire of such

a pair, both signals will be routed in parallel, keeping the distance

as defined in the net class.

This can't guarantee the same length for both signals, so there

will also be a new command that generates "meanders" to compensate

for length differences, or to create a fixed total length of a

differential pair.

Klaus Schmidinger

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