Hi,
Vortex:
> 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.
>
Owch. What does the USB standard say on that? *Somebody* must be at
fault here …
> 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.....
>
You can detect the presence of a resistor with fewer volts than five.
In fact, since it's a resistor, you can apply saif power to the D+ line
and check what's arriving at the +5V line. Again, I have no idea what
the standard says about that.
--
Matthias Urlichs | {M:U} IT Design @ m-u-it.de | [EMAIL PROTECTED]
Disclaimer: The quote was selected randomly. Really. | http://smurf.noris.de
- -
"If you did not know at the age of five that the gods are made
up beings and the myths impossible stories, you are a fool."
[Gaius Suetonius Tranquillus]
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