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'[EE] Reverse USB-Serial adaptor?'
2007\07\29@055420 by Howard Winter

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(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.

I suppose it's a tricky thing to do, since the USB interface is intelligent, and the peripheral won't just send data until it's done the enumeration thing -
but I thought I'd ask just in case it's been done!  :-)

Cheers,

Howard Winter
St.Albans, England


2007\07\29@072010 by Lee Jones

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> 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

2007\07\29@082829 by Xiaofan Chen

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On 7/29/07, Howard Winter <spam_OUTHDRWTakeThisOuTspamh2org.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

2007\07\29@090752 by Mike Harrison

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On Sun, 29 Jul 2007 04:21:14 -0700, you wrote:

{Quote hidden}

The Vinculum VNC1L chip is almost exactly this - I don't know to what extent it yet supports devices
other than memory and FT232's.

2007\07\29@122459 by Dr Skip

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Could you use a USB bridge to kludge it together? Not sure what you
would see or need on the PC end software-wise, but it would handle the
USB hardware host issue. Run one side to the device and the other to a
USB-to-serial device to the PC. Sima makes one and Tiger Direct carries
another model. It should at least get bits to your serial port I think.

-Skip

{Quote hidden}

2007\07\29@171204 by Herbert Graf

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On Sun, 2007-07-29 at 12:24 -0400, Dr Skip wrote:
> Could you use a USB bridge to kludge it together? Not sure what you

I don't see how. The ones available that I've seen are basically two USB
endpoint devices back to back. They are specifically designed for file
transfers between the two PCs. I don't think there is any "host"
capability in these devices. TTYL

2007\07\29@181238 by Marcel Birthelmer

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Howard,
have you considered cracking open the GPS unit and checking if it's
maybe just a USB-serial converter in disguise? Maybe you can just tap
the UART signals somewhere and splice in a 232 level converter or
something like that.
- Marcel

2007\07\29@201102 by Howard Winter

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Marcel,

On Sun, 29 Jul 2007 15:12:37 -0700, Marcel Birthelmer wrote:

> Howard,
> have you considered cracking open the GPS unit and checking if it's
> maybe just a USB-serial converter in disguise? Maybe you can just tap
> the UART signals somewhere and splice in a 232 level converter or
> something like that.

Thanks for the suggestion - I am tempted, but my recent "have a look inside" record rather puts me off.  I did this with a rather expensive mobile
phone, and it's now a pile of parts, some of which will never play the violin again... I used to be very good at taking things apart, and fairly good at
putting them back together, but my present eyesight and usual clumsiness, together with a very sophisticated physical design of the phone, are all
conspiring against me.

I'll wait until things improve and I think I can do it without wrecking it (I've lost a lot of the acuity in my right eye, which they tell me will get better
in a few weeks.  The only consolation is that the opthalmologist said that the condition (Central Serus Retinopathy) was "found in young males"!  :-)

Cheers,


Howard Winter
St.Albans, England


2007\07\30@063512 by Alan B. Pearce

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> 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

Well, I guess the GPS is going to look like an HID serial port, so getting a
USB-on-the-go chip, and setting it up to be a host HID serial port expector
would be a possibility. I think Cypress make USB-otg chips.

2007\07\30@112718 by Marcel Birthelmer

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Howard,
having just bricked an XBox with my abysmal soldering skills, I
completely understand your reluctance of having a look inside. Good
luck with your eye!
- Marcel

On 7/29/07, Howard Winter <HDRWspamKILLspamh2org.demon.co.uk> wrote:
{Quote hidden}

> -

2007\07\30@114230 by Joshua Shriver

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Good suggestion, I bought a GPS unit recently and when I plugged it
into my linux box I noticed the linux driver was used was actually for
a serial->usb.  I've also seen it in other product so it seems like a
common practice.

-Josh

On 7/29/07, Marcel Birthelmer <.....marcelb.listsKILLspamspam.....gmail.com> wrote:
> Howard,
> have you considered cracking open the GPS unit and checking if it's
> maybe just a USB-serial converter in disguise? Maybe you can just tap
> the UART signals somewhere and splice in a 232 level converter or
> something like that.
> - Marcel
> -

2007\07\30@124907 by Xiaofan Chen

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On 7/30/07, Alan B. Pearce <EraseMEA.B.Pearcespam_OUTspamTakeThisOuTrl.ac.uk> wrote:
> > 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
>
> Well, I guess the GPS is going to look like an HID serial port, so getting a
> USB-on-the-go chip, and setting it up to be a host HID serial port expector
> would be a possibility. I think Cypress make USB-otg chips.
>

HID serial port is a misnomer...
HID is a USB device class and typical USB serial port use CDC class.

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