Re: USB question

From: Jeff Nibler (djnibler_at_spam-me-not-hotmail.com)
Date: 08/10/04 

Date: Tue, 10 Aug 2004 12:56:30 -0700

Thanks Robert! 

-- 
Jeff Nibler
"Robert Wessel" <robertwessel2@yahoo.com> wrote in message
news:bea2590e.0408092234.47adddbc@posting.google.com...
> "Jeff Nibler" <djnibler@spam-me-not-hotmail.com> wrote in message
news:<cf8plg012su@enews2.newsguy.com>...
> > Rob and Tim, thank you both for your replies. One follow-up question...
> > assume some strange external device has a serial port connector. That
serial
> > port has an adapter connected to it which converts it to USB. That
device is
> > then a USB compatible device (client-mode of course) correct? Meaning,
if
> > you had a computer with USB host capability and a USB hub, you could
connect
> > several of those external devices to your computer via USB, and your
> > computer would be able to read both of them correct?
>
>
> Short answer:  Yes.
>
> Longer answer:  There are may USB->Serial dongles on the market.
> These all require some sort of device driver on the host, thus one
> particular model might (or might not) have Mac or Linux (or...)
> support.
>
> In theory, you should be able to have several of these gadgets
> connected at once.  In practice, the device drivers supplied with some
> of these makes that impossible (although the situation is better these
> days).
>
> Also, as compared to a "normal" serial port, the latency of control
> actions (flow control, for example) is usually quite high (there's a
> lot of buffering between the application and the serial port).  So a
> device that drops DTR (or CTS, or whatever) and expects that data will
> stop flowing in one or two bytes may be sorely disappointed, and may
> generate an overrun or lose data.  Likewise, if you're application is
> doing a lot of very time specific control of the various control
> signals, you're going to have problems.
>
> In short (and as always), before you claim these capabilities to a
> customer, you ought test them, with the particular device and serial
> port dongle in question.

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