Usb Host And Client

[Mjolinor]

Does anyone know enough about the host / client system on the Zaurus to tell me how it prevents damage when a client cable is plugged in.

With a client cable 5 volts is supplied from the host. This comes in the same pin as the 5 volt comes out of when a host cable is plugged in (I think). Why does this not cause a problem?

Reason for knowing.
I just bought a Nokia 770 and the USB native mode is client but it can be made into a host port. Given that the Zaurus does both at the same time and that the only difference between the two physically is the shape of the metal surround (small pliers and brute force fix that problem) I was going to look at making the 770 the same.

[pelrun]

In reality 5 volts does not "come out" of one side or the other. The direction of current flow depends entirely on the voltage difference, which would be small for two self-powered devices as both sides hold their power pin at the same potential relative to their common ground.

Anyway, the difference between host/client plugs is not just physical; one pin tells the socket what kind of plug it is.

[Mjolinor]

In reality 5 volts does not "come out" of one side or the other. The direction of current flow depends entirely on the voltage difference, which would be small for two self-powered devices as both sides hold their power pin at the same potential relative to their common ground.

But the direction of current flow is unknown and the current flow is not limited.

Anyway, the difference between host/client plugs is not just physical; one pin tells the socket what kind of plug it is. The USB charge pump IC which supplies the Z's USB power pin uses this to perform whatever power isolation is required.
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The secret being that the 5v host voltage is only connected when pin 4 is grounded so it looks like I need 5volts internal somewhere and a PNP transistor with base to pin 4 and emitter to pin 1 (with the odd resistor or two). FET being a better option probably.

Cheers

[pelrun]

And I took a second look at the schematic and datasheets and I don't think the host ID pin has any influence on whether the port is powered - that particular IC can only source a small current.

There's also a (non-toggled) regulator which is also attached to usb Vbus. It *is* current-limited; albertr and others have increased that USB current limit by changing a resistor attached to this second IC.

[louigi600]

In the USB OTG mini-A receptable in the pack of the Z there is 5 pins:
4 are the ordinary usb
1 is fevoted to sensing whether it sould operate on clinet or host mode.

The plug must therefor gave pin n.5 grounded to make the Z operate live a usb host ... or pin n. 5 not connected to anything (ot very high resistance to ground) to make the Z operate as client.

I've notes on my home page on howto make your own host adapter cable from scrap usb cables.

[utx]

The secret being that the 5v host voltage is only connected when pin 4 is grounded so it looks like I need 5volts internal somewhere and a PNP transistor with base to pin 4 and emitter to pin 1 (with the odd resistor or two). FET being a better option probably.

I guess, that it should be done by software, but it is not, at least in OZ/Angstrom. My colleague uses a client cable with gender changer to get a "host cable".

SPITZ_GPIO_USB_CONNECT: Detects, whether host cable is inserted.

SPITZ_GPIO_USB_HOST: Controls output power.

SPITZ_GPIO_USB_CONNECT: Does some measurements do detect connected device.

[utx]

Does anyone know enough about the host / client system on the Zaurus to tell me how it prevents damage when a client cable is plugged in.

I just bought a Nokia 770 and the USB native mode is client but it can be made into a host port.
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You probably cannot damage your Zaurus (at least SL-Cxxxx) with the default wiring - it has a current limiter set to 200mA. When you shorten two devices in host mode, then depending on the exact voltage, one of the devices should activate limiter and stop.

Nokia uses for some reasons client-only devices connector (OTG mini-B only) and you cannot use correct USB OTG mini-A cable there (mini-A connector has exactly the same wires {with ID line activated}, but has a bit larger shield on the sides to prevent accidental putting of mini-A cable to client-only device connector). They probably consider USB host mode as unsupported.