About Intel Pxa27x-processor And Usb-capabilities

[ChrisZ]

Hi!

I've just read in the Intel PXA27x-specification. And there are some interesting things about the USB-capabilities of the processor:

USB-client: USB 1.1 with max. 12 Mbps

USB-host: USB 1.1 with max. 12 Mbps. The host provides 3.3 V to clients but the normally necessary 5 V for HDD or something "bus-powered" are not provided. And, the 3.3 V output is combined with a max. current of 25 mA and therefore 82.5 mW. That's much too less for a harddisk. According to Toshiba, Hitachi, Seagate and Fujitsu, current 1.8 inch harddisks need at least 1.2 W for spin-up.

Intel (see ftp://download.intel.com/design/pca/appli...als/2800002.pdf and ftp://download.intel.com/design/pca/appli.../28000502.pdf):

The +5 V VBUS source from USB host controller, which must be available for bus-powered peripherals, must be supplied from an external source, but it is not part of the PXA27x processor silicon.

I don't think Sharp added some additional USB functions which were not provided by the PXA270.

It's too bad, I really thought I could use an external HDD without power supply.

[barbjfox2000]

Chris,

Thanks for illuminating. Since I don't speak Japanese, it's been a bit of an adventure finding out what the "true" capabilities of my marvelous new device actually are!

[omega]

If you look around, wasn't there something mentioned about a io port? I also saw something suggesting that there was a serial port in this io port. My io port (C860) has a VCC output... But this of course will only be 3.3volts... wouldn't advise using a step-up convertor, unless you were going to take from the battery directly...

[bluedevils]

It shouldn't surprise you that a desktop HDD's power consumption is not supported by the Zaurus.  The Z itself is considered a power hog and attaching a hard drive will kill it quick.  Think of it this way.  The old IBM microdrives generate more heat than the new Hitachi.  The old ibm microdrives impact the Z's battery life considerably.  Now feel the heat generated by your desktop's hard drive.

If you were thinking about using it while powering the Z externally, then maybe it would be easier to get a beefier transformer with two outputs.

[ChrisZ]

It shouldn't surprise you that a desktop HDD's power consumption is not supported by the Zaurus...

@bluedevils: You're right. But I thought it could be possible to power an external 1.8 inch harddrive with the Zaurus, not a desktop HDD. Remember: current 1.8 inch drives need only 1.2 W for operation. That's really not much and compared to the Hitachi Microdrive 3K4 which needs already about 1.0 W, 1.2 W is really impressive!

@omega: I didn't see anything with 5 V. But I 've just looked at the processor's specs.

One more thought: Some drives, e. g. Toshiba MK3006GAL, need just 3.3 V and about 1.2 W. Perhaps  they can be powered with an other power source from the Z, e. g. the IO-port. but I don't know what max. current is provided by it.

By the way, I've decided to buy an external 2.5 inch drive with an external power source. That works without any problems. It can be powered with the same external power supply which I use for the Z. I think that's a good solution.

[bluedevils]

My error.  I did not realize the 1.8 inch's power requirements were much less than a normal desktop's HDD.

[ChrisZ]

Errors everywhere:

I've taken my Z and meassured the USB bus-power. And ... 5 V.

That means: the PXA27x doesn't provide 5 V. But if someone (Sharp) uses the processor and wants to use USB in a device, one must take the 5 V from an other source. Sharp found such a source :-)

But that doesn't answer the question how much max. current is on the USB bus. Perhaps some 1.8 inch devices work.

[bluedevils]

Did you measure that with the Z plugged in or when it is using battery power?  I ask this because external power is 5v, but my 760's and 6000's batteries are 3.7v (is the 3000 different?).

[ChrisZ]

Without power supply.

The battery is 3.7 V too.