On Fri, 26 Dec 2008 22:31:37 -0800, John Navas
put finger to keyboard and composed:
On Sat, 27 Dec 2008 12:56:05 +1100, Franc Zabkar
wrote in
:
On Sat, 27 Dec 2008 11:14:49 +1100, Franc Zabkar
put finger to keyboard and composed:
On Fri, 26 Dec 2008 12:33:36 -0800, Pat Cheney put
finger to keyboard and composed:
One problem I've found with cellphones is Motorola. For some reason,
Motorola USB is "special" USB.
I've found that Motorola chargers work fine with all other phones but
Motorola phones don't work well with the other chargers.
The difference could be just one resistor:
http://pinouts.ru/CellularPhones-A-N...r_pinout.shtml
I also believe that some devices will look for the presence of pullup
or pull-down resistors on the Data+ and/or Data- signal pins. In this
way the device knows when it is connected to a USB host, in which case
it will limit its current draw to 500mA. Otherwise it thinks it is
connected to a fast charger, and then it draws whatever current it
wants.
People, people, enough with the mystery and speculation -- this is part
of the USB standard! It's called ID, and is clearly defined. See
http://en.wikipedia.org/wiki/Universal_serial_bus#USB_cables
I prefer this more informative article:
http://en.wikipedia.org/wiki/USB_On-The-Go
"OTG" is an extension to the USB standard that enables a device to
function either as a host or as a peripheral.
"A key usage case is a mobile phone that can be a Default Host to a
Mass Storage memory stick or a Default Peripheral to a PC."
"The OTG cable has a micro-A plug on one side, and a micro-B plug on
the other (it cannot have two plugs of the same type). OTG adds a
fifth pin to the standard USB connector, called the ID-pin; the
micro-A plug has the ID pin grounded, while the ID in the micro-B plug
is floating. The device that has a micro-A plugged in becomes an OTG
A-device, and the one that has micro-B plugged becomes a B-device (see
above). The type of the plug inserted is detected by the state of the
pin ID."
"USB OTG defines two roles of devices: OTG A-device and OTG B-device.
This terminology defines which side supplies power to the link, and
which is initially the host. The OTG A-device is a power supplier, and
an OTG B-device is a power consumer. The default link configuration is
that A-device act as USB Host and B-device is a USB Device. The host
and device modes may be exchanged later by using HNP (Host Negotiation
Protocol)."
So in order to connect a phone to a PC host, the phone must power up
as a power consumer, and as a peripheral. This in turn means that the
ID pin must be floating. Similary, if the phone is connected to a
charger, then the ID pin must be floating also. If it were grounded,
then the phone would be trying to put power on the cable.
It seems to me that it would be a very straightforward matter to
determine the actual connectivity of a Blackberry or Motorola mini-USB
cables. Just break out a $10 DMM, clamp the ends of the cable in a
vice, extend the DMM probes with sewing needles taped to the ends, and
then measure the resistances between the pins. That should put any
unsubstantiated assertions quickly to bed.
The pinouts.ru URL which I alluded to earlier clearly demonstrates
that Motorola uses some kind of proprietary passive signalling method
at the charger end of the cable. It does not suggest, and nor did I
suggest, that the actual cable is any different than a standard cable.
I'm assuming that the original charging cable has 5 pins at both ends.
If it has 4, then that creates a problem, unless the required resistor
is embedded in the cable, which would then make the cable
non-standard.
Did I say I was confused?
- Franc Zabkar
--
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