On Tue, 12 Jun 2007, Vortex wrote: > Thank you for this very helpful hints! > I had a look at the waveforms on the USB-Bus and discovered > that the impedance between my hardware and the laptop is > completely missmatched. According to an example application design from > dallas semiconductor i used 2x30pF on D+ and D-. But on the Notebook > side there are about 300pF. After matching this, everything > works perfectly. Don't know which one of the two devices is the bad > one now but it works....
For your information, here's what the USB spec says: 7.1.6.1 Low-speed and Full-speed Input Characteristics The input impedance of D+ or D- without termination should be >300 kOhms (ZINP). The input capacitance of a port is measured at the connector pins. Upstream facing and downstream facing ports are allowed different values of capacitance. The maximum capacitance (differential or single-ended) (CIND) allowed on a downstream facing port of a hub or host is 150 pF on D+ or D- when operating in low-speed or full-speed. This is comprised of up to 75 pF of lumped capacitance to ground on each line at the transceiver and in the connector, and an additional 75 pF capacitance on each conductor in the transmission line between the receptacle and the transceiver. The transmission line between the receptacle and RS must be 90 Ohms +/- 15%. The maximum capacitance on an upstream facing port of a full-speed device with a detachable cable (CINUB) is 100 pF on D+ or D-. This is comprised of up to 75 pF of lumped capacitance to ground on each line at the transceiver and in the connector and an additional 25 pF capacitance on each conductor in the transmission line between the receptacle and the transceiver. The difference in capacitance between D+ and D- must be less than 10%. Alan Stern ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
