OT: What's in a USB cable?

Mike O'Dell mo at ccr.org
Sat Jan 5 19:31:08 CST 2013

yup - leaving an antenna connected to a USB port is a bad idea, 
especially a USB 2.0 port

the "device enumeration" which takes place to allow "hot-plugging" USB 
goobers is a non-trivial
process which ties-up the CPU for stretches because the guys who 
designed the USB protocols
made the classic mistake of assuming the computer has nothing better to 
do that wet-nurse
USB host control chips, especially when it's doing a "hot-plug" 
operation because what on earth
could be more important than plugging in a USB Nerf Cannon?  There are 
better controller chips
which take less CPU intervention, but there are a lot of USB 1.0 and 
early 2.0 ports out there with
really, really brain-dead controllers.


On 1/5/13 8:15 PM, Phil wrote:
> Hi Iain
> I've had similar problems myself. When my laptop has an unterminated 
> USB cable plugged into it, the USB "ding" indicator sometimes stutters 
> as though it thinks that a device is being rapidly and randomly 
> connected and disconnected, and it seems to divert all its system 
> resources to trying to recognize the newly 'attached' device, which 
> causes the computer to similarly stutter. I have always assumed that 
> this is just noise pick-up from the (unterminated) cable.
> Phil M1GWZ
> On 6 Jan 2013, at 00:10, Iain McFadyen wrote:
>> I have a Standard USB-A to Micro USB-B cable, with a Blackberry logo 
>> stamped on the Micro-B end.
>> I use this cable for various purposes from time to time: recharging a 
>> dumb cellphone, recharging an FRS radio, and syncing/charging a 
>> Blackberry Curve to the Blackberry desktop software package.
>> When I leave this cable plugged in to a PC port, but with nothing 
>> plugged in to the Micro-B end, my PC plays up. The cursor hesitates 
>> as I drag the mouse across the screen.
>> The problem disappears when the Standard end of the cable is 
>> unplugged from the PC.
>> Question: Is there any active or passive component embedded in this 
>> cable? I see no reason for any components, the VBUS, D+ D- and GND 
>> pins should be wired pin-for pin, and the ID pin at the Micro end 
>> should be open, right?
>> Your thoughts please...
>> Iain KI4HLV
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