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[aprssig] USB and Rs-232 GPS's

Scott Miller scott at opentrac.org
Fri Jul 30 17:54:52 UTC 2004


> Could some one tell me if a hockey puck GPS that has a USB can
> be converted to use RS-232.  I have heard USB is just a serial
> protocol that can supply power and ground but I did not think it had
> the same voltage levels as RS-232. Is this correct?

It's a serial protocol, but so is Ethernet.  No, there's no simple way to do
a conversion - USB depends very heavily on the host.  Pretty much everything
is actually initiated by the host - a USB device won't even send any data
without being polled.  Because of the host requirements and the fact that
there are so many different ways the data could be sent (control, bulk,
isochronous, interrupt), there's no way to make a generic USB to serial
converter.

I've seen some USB GPS receivers that have serial cable options - I think in
that case they at least have TTL level RS-232 outputs already that the cable
uses, and they're not doing an actual conversion.

Scott
N1VG





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