Re: USB question
From: Robert Wessel (robertwessel2_at_yahoo.com)
Date: 08/10/04
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Date: 9 Aug 2004 23:34:33 -0700
"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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