Re: An 80 port USB Board

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snipped-for-privacy@u18g2000prn.googlegroups.com>, snipped-for-privacy@gmail.com says...
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....

Already is the case, so nobody has enough USB sockets.

Wait for the PC/laptop that has 80 sockets for all the devices to be20%
plugged in.
20%
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When no enumeration has taken place about 90mA, you can only get 500mA
AFTER a data exchange to do enumeration.

--20%
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Re: An 80 port USB Board


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That's the theory, but in practice most machines don't bother and just give
500mA. Every machine I've tried has.
And powered USB hubs are supposed to give 500mA without question.

Dave.

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Re: An 80 port USB Board


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I have read about that too, but in practice, I have had no problems
with powering "dumb" devices (ie: ones that only connect to the power
pins and dont utilise the data pins) from USB ports drawing currents
substantially in excess of 90ma.  (tested only up to about 400ma)

I have only tried this on various ASUS motherboards though, not
laptops.


In reality, one of the real limiting factors can be that the +5v wire
in the various USB cables, as well as the wire between the USB sockets
in the front of cases and the cables to the motherboard,  is not of a
sufficient thickness to avoid voltage drops when the device at the end
is drawing currents at the upper end of the limit.

We actually had a USB lead in the workshop with the +5v and ground
wires cut and brought out of the cable at both ends, and a thicker
wire (0.5mm sq) running on the outside of the cable to the other end
to avoid this problem when testing some devices.

Some Portable USB hard drives (laptop type) were notorious for this
problem, but I have noticed that modern USB cables seem to be a lot
better in this regard - possibly for the very reason that these
portable drives have become more popular in recent years, whereas I
cant remember seeing these around when USB was first introduced.

I doubt that these drives would have had much of a data transfer rate
in the early days until USB 2 speeds came along.





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