Thomas Andersson wrote:
> On 2010-12-16 01:40, Paul wrote:
>
>> Intel Southbridges in the past, have had OC# input pins on them.
>> Your overcurrent message, may be causes by that OC# input pin seeing
>> a change in state. So what you've observed, could be consistent with
>> a USB short circuit, and the Polyfuse protecting the port, opening up.
>> Polyfuses don't need to be replaced, and as soon as they're allowed
>> to cool off, they will conduct again.
>>
>> http://en.wikipedia.org/wiki/Resettable_fuse
>>
>> ATX_Supply --- 5V ---- Polyfuse ------+------ USB Port --- USB Device
>> |
>> Southbridge <----- OC# --------+
>>
>> OC# stands for "OverCurrent, active low". The logic signal becomes
>> true, at zero volts. If OC# is used to monitor the bus, then it
>> becomes true, when the Polyfuse opens, and the bus voltage drops to zero.
>
> But wouldn't that affect all USB devices then? As it is now only the
> mouse triggers the error message, if I dissconnects it everything is
> fine. I can reconnect it after booth but it fails to work properly.
>
What happens if you disconnect the mouse, wait two minutes,
and move it to another port. Does it work then ?
*******
To give an example of the wiring of that feature, there is
a reference schematic for an 875 era motherboard here.
http://developer.intel.com/design/ch...ics/252812.htm
If you open 25281202.pdf and go to PDF page 35, you can see the
eight OverCurrent signals. There is one per port. The Southbridge
controls up to eight ports. (OC0* to OC7*, the * meaning active
low, similar to #). The OC signals are wired in pairs, and that
is because the powering scheme for the USB port, also works in
pairs. A power failure, affects the two USB connectors in a
"stack". And the OverCurrent Status signals on two ports, are
triggered at the same time.
Moving to another stack, should give a "fresh start", in terms
of USB state.
The circuit that monitors the ports, is shown on PDF page 83.
The thing labeled THRMSTR (thermistor), is the Polyfuse. The
MMBT3904 transistor connected to PWRGD_3V_R appears to
be gating the OverCurrent indication, such that an OverCurrent
error is only reported, if the 3V rail is running. If the
THRMSTR opens, the bus voltage drops to zero, and
USB_OC_BACK_RIGHT drops at the same time (signaling there
has been an overcurrent failure). It's something along
those lines.
You could always fit another cord to the mouse, but that
wouldn't be a lot of fun. Opening the mouse, and
seeing how the cord terminates to the PCB, would
give you some idea how hard it would be to install
another one. You'd need a soldering iron, if the
wires are soldered into place. You can cut off the
old wires, but the new ones will have to be soldered
into place, for best results.
Paul