On 7/29/07, Howard Winter <HDRW@h2org.demon.co.uk> wrote:
> (reposted with tag)
>
> Does anyone know of a "reverse" USB to serial adaptor?
>
> 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 and I  want to use it with something that isn't a PC and
> which expects RS232.
>

That is not possible unless your GPS receiver has the USB host
function and support USB CDC-ACM protocol. This is very tricky
to implement. USB is host centric. You need a host driver to manage
the USB link.

Even Windows CE device with USB host function does not have
built-in CDC-ACM support. There is a third party driver though
and it requires quite a bit of adaptation. Eg:
http://www.cygnal.org/ubb/Forum9/HTML/001331.html

In the Microchip Forum, this kind of question keeps pop up. The current
PIC USB MCU is slave only.

Some of the Atmel AVR USB device support limit hosts function
(OTG) and you might be able to find some example. In fact,
they have a CDC implementation for AT90USB. So you might
be able to do it.

It is said that a PIC24 with OTG function will soon come out...

Xiaofan
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