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Fix USB assignements. Was RE: [aprssig] NEW laptop for APRS witha Serial Port?

Dave Baxter dave at emv.co.uk
Wed Apr 16 10:01:08 UTC 2008


Hi Jason...

In my experience here, with several USB<>RS232 devices from all sorts of
makers (single and multiple port) you can indeed "Fix" their virtual COM
port assignments, in Windows XP and 2000 at least.

I have had though, on one occasion some part of the Windows Update
scheme (we suspect) scramble the assignments, needing it to be done
again.  But that was (so far) a once only event some months back, on an
older W2k machine.  (I think it may have been a long overdue SP4
update?)

I have no experience of Mac OS's, and only little of Linux, so cant
comment on them

As to the unique ID number (I forget what exactly it is called)  The
last time I had to read the USB spec' (serious brain ache) it's
described in there.   This is the physical hardware ID, not the
programmed in Makers ID, that a company pays dearly for. 

They have to be unique, as the USB physical transport data format is
very much like a network, so you have to have unique per-device hardware
ID's, in case you connect multiple devices of one type to one hub.

I realy do not want to have to go back and read that spec again!....

!!APRS!!    To try and vaguely keep on track....

73.

Dave G0WBX.


> -----Original Message-----
> This is a good theory, but I have had problems both with Mac 
> OS X and Linux when trying to use this method.  It is 
> certainly conceivable that Windows does a better job in this 
> respect, but long experience with Windows in general makes me 
> doubt it...
> 
> Are you sure this is based on port assignment, or is is 
> enumeration order?
> 
> >  Note:  USB devices have a unique ID number, much like a 
> network card 
> > MAC  address.
> 
> This is sadly not the case.  FTDI devices do, but as best I 
> recall Prolific and SiLabs devices do not.  I don't know 
> about Keyspan, as they attempt to use a name based on 
> enumeration order on OS X.
> 
> Most of these devices work just fine until you plug it in to 
> a different port or, even worse, use more than one.
> 
> -Jason
> kg4wsv
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