> Does anyone know of a "reverse" USB to serial adaptor?  

I've never heard of such a beast existing.  Some comments...

> That is, one into which a USB peripheral is plugged, and which
> produces a serial output - in  this case it's a GPS receiver
> with a USB interface

So the GPS unit has a device/peripheral side USB connection
(probably B or mini-B connector)?  Does the manufacturer provide
a driver for the PC (or Mac or Linux) side?  If so, how will you
simulate that in a reverse USB to serial adapter?

> and I want to use it with something that isn't a PC and which
> expects RS232.

If this something is expecting to talk to a GPS unit via serial
port, does it use (somewhat-standard) NEMA sentences or does it
rely on a proprietary protocol to the GPS unit?  Proprietary
would make this whole lash-up less likely to work.

You could conceivably have 2 proprietary protocols here -- one
on the GPS USB link and a second on the serial link.  How fun.

> I suppose it's a tricky thing to do, since the USB interface
> is intelligent,

And USB is non-symmetrical.  You need host-side USB connection
to master the link to the GPS unit.

You could build one with a Cypress SL811HS USB host controller
and a PIC with UART, but it wouldn't be a trivial exercise.

Good luck.
						Lee Jones

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