I don't have a full answer but I can say that not all USB-to-RS232
converters or cables are equal. A similar problem was reported in one
of my astronomy groups (re: telescope control) and one enterprising
person did some sleuthing.

Success or failure depends on the USB-RS232 converter chipset. Here's
what the guy discovered:

Available Chip(set) Names:

FTDI
Prolific PL230
MCT U232/F5U109
USA-19HS

Of all the chips used, only the MCTs are known to be problematic on
the EQDIR interface. The MCT chips are used in the Belkin/Targus
models.

Thank you for the reply and information. I will certainly be making
use of it.

I should have said my Ubuntu machine doesn't even acknowledge a cable
is plugged in. I think I must need to install something to use the
cables. Does the device on the RS-232 need to send some kind of
identifier back through the cable?

I don't fully understand your question. A USB cable. by itself, is a
passive aggregation of wire and connectors. If you just plug the
cable into a computer nothing will happen.

The other end of the USB cable must be plugged into something (such as
a USB hub, CF/SD card reader, printer, etc.) before the computer will
"see" what's there. If the device to which the other end is plugged-in
is a USB-to-RS232 converter, the computer and the device will initiate
some hand-shaking and (possibly) install a driver for the device if
one isn't already installed.

As far as RS232 goes, the only identification that could/would be
returned to the computer would be whatever your application program
has requested from the RS232 device. This is very device/application
dependent. FOr example, my chip/EPROM burner doesn't do anything on
the RS232 line until the app program begins talking to it. Same thing
with my telescopes which use RS232 for remote control.

If you could supply some more info about what it is you're attempting
to connect up, more help could be provided.

I'm having a lot of trouble with terminology. For instance I
expected books to index this subject under "RS-232," "Serial,"
and "Port." Now I see it's indexed under "stty." I'm looking for a
command that sends a file through the cable so I can observe the
result on a break-out box.

Physically the each cable has a USB connector, about one meter of
cable, a box or bulge, and a short bit of cable to an RS-232
connector. I'll try to have some information when I come to the
internet coffee house tomorrow.

If it is supported and working, the USB to serial adapter should map to
/dev/ttyUSB0.

http://www.linux-usb.org/USB-guide/x356.html

Here's more about the cables I'd like to use with Ubuntu:

Kosmos USB-COM-Adapter, Art Nr 703 921 contains a Sipex SP232EEP DIP
IC and a second IC on the board under a blob of black plastic. This
came with a Thames and Kosmos Toys kit with an Atmel ATTINY2313-20SU
microcontroller. With the Thames and Kosmos application loaded under
Vista this cable works. It does not work with the other
applications.

Radio Shack USB Special Cable, color white with no other markings. I
can not open the molded circuit box without destroying it. I bought
it to use with the BASIC Stamp microcontroller learning kit Radio
Shack sells. Does not work with Radio Shack's BASIC Stamp
application loaded under Vista. When the application is loaded on my
Lenovo laptop (when it had Vista on it), connecting the battery to
the BASIC Stamp board kicked the Lenovo into Visa's white screen of
death mode.

I though I had tried a third cable. But it was something else—USB to
propriatory protocol.

Now that you got me to take a closer look at these cables I realize I
should get a general-purpose USB-to-RS232 adapter cable with a
recommended chip set.

At first I didn't realize you were talking about a "smart" USB cable
with the electronics built-in.

A moment ago I looked at several electronics vendors web sites and
found more of the same. FOr example, at Frys.com there was such a
cable from Parallax for their STAMP system; it apparently doesn't
work with anything other than Parallax products (from the description)

Same for Garmin; their USB to RS232 is only for their GPS products.

And everyplace else I looked, same story.

Getting a generic USB-to-RS232 convert box seems the best solution.

There are two other solutions:

1. if your system is a laptop, there are PCMCIA cards that provide a
true RS232 interface. THese seem a bit pricey, though.

2. if your system is a desktop and has a spare PCI slot, there are
many 1-/2-/more-port RS232 cards that seem reasonably priced.

I just took a look at the last 3 computers I bought and none of them
have RS232 ports, so I'm going to buy 1 or 2 PCI cards so I don't
lose the capability of working with RS232 devices. All my Dell laptops
have RS232 ports, and a new one I've been lusting after (a Latitude
D630) has one also but its price is beyond my present budget.

Hah! I just went to Dell's site and in the reviews for the D630 one
guy wrote "I did not even boot this laptop to the installed windows
operating system. The first thing I did was install ubuntu."

Now I'm going "Duh." Why didn't I check the Parallax web site.

My 2 beginners' and 3 more detailed books are indexed by bash
terminology. Somehow I escaped learning much bash jargon in my MS
Windows days ;-) I think Ubuntu could gain more converts if the
authors of Ubuntu books included index entries like "RS-232 see
tty," "serial see tty," "port see ____," and so on.