Eben King wrote:
> On Thu, 10 May 2007, Mark Polhamus wrote:
>
>> Eben King wrote:
>>> Anybody used a USB <-> serial cable? I had this bright idea of hooking
>>> my UPS to the computer. I understand lots of nifty stuff can be
>>> accomplished through such a connection.
>>>
>>> Unfortunately, my UPS's cable is serial on both ends, and my computer's
>>> sole serial port is occupied by a modem. I looked aroung for a USB
>>> variant. Since the "S" in "USB" stands for "serial", I thought it
>>> shouldn't be too hard to find. Unfortunately, it was. The only USB
>>> cables I found had an RJ-45 on the other end.
>>>
>>> So, I figured I could put either the modem (it only gets Caller-ID data,
>>> so flow control and speed aren't that important) or the UPS (2400 BPS
>>> sez the manual, so ditto) on the USB <-> serial cable I have. But, I've
>>> never used it but once (and that was in The Other OS). Help?
>
> I tried plugging the UPS into the USB <-> serial cable, but:
>
> On the first attempt, everything was "live" when I inserted the plug
> (DB-9) and the UPS shut off immediately. Crud. OK, now that it wass
> down, things weren't likely to get worse, so I went ahead and hooked it
> up. The UPS came up OK (as long as I let it finish the self-test before
> booting the computer).
>
> Then, during the boot sequence, the UPS powered off. My guess is that
> when the USB port is initialized, the transition from "no power" to
> "power" makes the converter go through an initialization sequence, part
> of which means "shut down now" to the UPS. Said sequence is not a
> concern to the modem (and in any case it's rather less vital) so I
> switched the connections.
>
>> I've used USB to Serial converters on Linux and Windows. They
>> actually work better on Linux since drivers are built into recent
>> kernels and there is nothing to install. They present a virtual comm
>> port interface, so to your software they look just like another serial
>> port, "/dev/ttyUSB0" or some such.
>
> Thanks. I found out about "lsusb" so I could find what my device
> _really_ is.
>
>> Keyspan model USA-19HS is the one I have used the most, which has some
>> sort of TI chip.
>
> lsusb says:
>
> Bus 001 Device 005: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial
> Port
>
> so I went in the kernel configuration and compiled
>
> <M> USB Prolific 2303 Single Port Serial Driver
>
> Modprobed it, udev created the node /dev/ttyUSB0, and off I went. Not
> sure what'll happen next time I boot.
>
>> Had multiples plugged in at the same time, it all just works,
>> although you have to pay attention to make sure you associate the
>> correct device entry with each converter.
>
> Are they differentiable by udev, or once it's created the devices it's
> up to you to figure out which one is ttyUSB[0123]?
I've always just looked through /var/log/messages to figure out which is
which. There is probably a better way.
-- Mark
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