[CUBE] [CUBE]

[atoa at krak.net]

That's all very good, but it doesn't say anything about a maximum for a 
port. There's no doubt that the maximum load for a device is 5 units of 
100 mA. But is a port that can deliver more than 500 mA out of spec?


On Sat, 7 Aug 2004, Steffen Barabasch wrote:

>> 2) Looking at Table 7-7 of the Universal Serial Bus Specification
>> Revision 2 reveals that Minimum High Power Port (out) is in fact 500 mA.
>> There is no maximum stated. What am I missing?
>
> This section in the original USB specs:
>
>> The power source and sink requirements of different device classes can be 
>> simplified with the introduction of the concept of a unit load.  A unit 
>> load is defined to be 100mA.  The number of unit loads a device can draw 
>> is an absolute maximum, not an average over time. A device may be either 
>> low-power at one unit load or high-power, consuming up to five unit loads. 
>> All devices default to low-power. The transition to high-power is under 
>> software control.  It is the responsibility of software to ensure adequate 
>> power is available before allowing devices to consume high-power.
>
> ;-)
>
> The "minimum" stated is probably the minimum power that ports and powered 
> hubs should be able to supply, not the minimum devices could draw, since that 
> would mean that I could draw 10A, and that's certainly not what they meant.
>
> BTW, any powered hubs that can't drive the Cube speakers are probably out of 
> specs themselves and simply might have problems with the power draw of the 
> amp (even if it's not in "booster mode" as on the Cube ports).
>
> Steffen
>
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