B.J. said:
thanks for the response! could you exlain to me more about powered hub or
"y" cable? is it different from the cable that came with the player? the
instructions for mp3 says not to use a different cable.
I was hoping for more background info. Which exact brand and model of
MP3 player. Which brand and model of pre-built computer or which
brand and model of motherboard is supplying the USB port.
USB has a 5V at up to 500mA supply per port. I'm not sure exactly
what the computer is supposed to do, on an overcurrent. On an Asus
motherboard, for example, an automatic fuse (Polyfuse), disconnects
the power when it goes over an amp (1000mA) shared by two ports.
One fuse feeds two ports. On things like laptops, a more precise
current limitation may exist. There are small chips that perform
a current limiting function at the 500mA value.
"Implementation Strategies for USB Circuit Protection Technology"
http://www.ce-mag.com/archive/03/ARG/mikolajczak.html
If a Polyfuse was opening, the flash rate of the MP3 LED would be
quite long. The fuse has to cool off, before it will let power flow
again. A current limiting chip could respond faster, when the load
is removed, recovering instantly.
When a USB device is enumerated, some of the data that comes back
includes an estimate of the devices requirements. For example, my
mouse right now, says it needs 100mA in its enumeration. To read that
value, the mouse, when plugged in, is checked for its vital statistics,
by the system probing the enumeration information. The software may
decide, based on summing the currents required by a USB device, that
sufficient power is not available. And then the device could be
denied based on that kind of determination.
It means, potentially, there are two ways a power limit could be
detected. It could be detected physically (Polyfuse or current limiter
chip), or it could be detected logically (power requirement stated
in enumeration info at first probing). A typical situation with logical
limit, might be on a bus-powered external hub, plugged into the
computer. (100mA ports, unable to supply a 500mA device.)
By asking you for more info on the hardware, my intention is to run
some searches using the model/brand info, and see if there are other
reports of this problem.
If you could get the MP3 player to stay connected logically, long
enough, you might be able to read out some info from it. This program
displays the enumeration info from USB devices plugged right into
the computer. I'm providing an archived page, because the original
page on the Microsoft site has been moved. The download program
is called "UVCView".
http://web.archive.org/web/20070516...com/whdc/device/stream/vidcap/UVCViewdwn.mspx
The screen on the program, will look similar to this picture. If the
device will stay connected long enough, you may be able to capture
the information and copy it into a posting.
http://www.die.de/blog/content/binary/usbview.png
On my mouse, this is the field in UVCView, that states the
power requirement.
MaxPower: 0x32
The number is hexidecimal, and the units are 2mA per unit.
0x32 = 3*16 + 2 = 50. Multiplying 50 * 2mA = 100mA. So
0x32 means 100mA. A value of 0xFF hexidecimal, would be
510mA, but values that high would not normally be reported
by a device (as 500mA is the limit in the standard).
The following picture is a "USB Y cable". Of the two heads
on the left, one uses all four contacts, while the second one
uses only two of its contacts. The second one is used to
steal more power. By drawing 500mA from each connector on
the left, the device allows 2.5" external USB hard drive
enclosures, to draw more power than normal. Normally, this
kind of solution, is not required for devices other than
2.5" drive enclosures.
http://secure.serverlab.net/shop/graphics/00000001/yCable.jpg
So, of the above, at least tell us what brand/model of MP3
player this is. A nice exact name, suitable for searching.
Paul
