OESF | ELSI | pdaXrom | OpenZaurus | Zaurus Themes | Community Links | Ibiblio

IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
> Usb Host And Client, How does it work
Mjolinor
post Aug 15 2007, 03:16 AM
Post #1





Group: Members
Posts: 227
Joined: 26-October 05
Member No.: 8,405



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.
Go to the top of the page
 
+Quote Post
pelrun
post Aug 15 2007, 03:36 AM
Post #2





Group: Members
Posts: 369
Joined: 6-September 04
From: Brisbane, Australia
Member No.: 4,488



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.
Go to the top of the page
 
+Quote Post
Mjolinor
post Aug 15 2007, 03:51 AM
Post #3





Group: Members
Posts: 227
Joined: 26-October 05
Member No.: 8,405



QUOTE(pelrun @ Aug 15 2007, 12:36 PM)
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.

QUOTE
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.
*


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
Go to the top of the page
 
+Quote Post
pelrun
post Aug 15 2007, 03:25 PM
Post #4





Group: Members
Posts: 369
Joined: 6-September 04
From: Brisbane, Australia
Member No.: 4,488



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.
Go to the top of the page
 
+Quote Post
louigi600
post Aug 19 2007, 01:32 AM
Post #5





Group: Members
Posts: 474
Joined: 21-May 06
Member No.: 9,928



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.
Go to the top of the page
 
+Quote Post
utx
post Sep 5 2007, 02:54 PM
Post #6





Group: Members
Posts: 135
Joined: 27-June 05
From: Prague, Czech Republic, Europe
Member No.: 7,468



QUOTE(Mjolinor @ Aug 15 2007, 01:51 PM)
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.
Go to the top of the page
 
+Quote Post
utx
post Sep 17 2007, 02:36 PM
Post #7





Group: Members
Posts: 135
Joined: 27-June 05
From: Prague, Czech Republic, Europe
Member No.: 7,468



QUOTE(Mjolinor @ Aug 15 2007, 01:16 PM)
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.
*


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.
Go to the top of the page
 
+Quote Post

Reply to this topicStart new topic
2 User(s) are reading this topic (2 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 30th October 2014 - 04:16 AM