Am Mittwoch, 13. Juni 2007 06:50 schrieb Vortex:
> Hello!
>
> I investigated the setup again at last weekend.
>
> Somebody on linux-usb Mailinglist explaind the "failed with status
> 500000" message. And so i decided to check the waveforms on D+ and D-.
> I've discovered that there is a complete impedance missmatch between
> the ds2490 and the usb-port of this laptop.
> In the datasheet from dallas there are 30pF capacitors recomended
> on D+ and D-. But on the Notebook side there are at least 300pf
> expected. So i have added capacitors to my circuit at D+
> and D- and everything works well now.
>
Hm. The DS2490 datasheet lists these capacitors as optional on page 33.
> The +5V Power Supply on the Notebook (and all other USB hosts
> reachable) is turned on as soon as the notebook is powered up.
>
Ok.
>
> Wouldn't this be a chicken and egg problem? The 1.5k resistor couldn't
> be detected if the +5V power isn't turned on. And the +5V power wouldn't
> be turnd on if the 1.5k resistor isn't detected.....
>
I had in memory the +5V line is not cut but tied to GND in that case. I'm
maybe wrong with this.
However, the host may cut the power to a USB port. But now I'm not longer sure
when this happens (besides from overcurrent).
Kind regards
Jan
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