[Nut-upsdev] megatec driver and usb-to-serial converters

Peter Selinger selinger at mathstat.dal.ca
Thu Nov 2 03:53:39 CET 2006

Hi Carlos,

as far as I know, there is a standard "serial over USB" interface.  I
think the USB specification discourages such interfaces.

All the "serial over USB" devices that I have seen have used a
manufacturer-specific hack. So connecting to a USB device should not
usually be as simple as connecting to /dev/something. 

If I am wrong, somebody please correct me! -- Peter

Carlos Rodrigues wrote:
> Hi all,
> Currently, the "megatec" driver only supports UPSes which have a
> serial (RS232) interface.
> However, I'm under the impression that most of the models that speak
> the megatec protocol, and have an USB interface, just have a standard
> serial-to-USB converter inside. This being the case, there should be a
> "/dev/ttyUSBx" device which the megatec driver could use just as if it
> were talking to the UPS over an RS232 cable.
> But... either this isn't the case, or these converters aren't
> recognized by the kernel's "usbserial" driver as such, and all that
> needs to be done is just convice the kernel to see the converter.
> This is something that I would like to know (even if just to be able
> to point people who email me about not having serial ports available,
> or with models that lack a serial interface, in the right direction).
> So, if someone out there with an UPS supported by the "megatec" driver
> (and with an USB interface) wants to try this, I would appreciate the
> feedback...
> Here are the general steps:
>   1. Connect the UPS using the USB cable (AFAIK, the USB and serial
> cables can't be connected simultaneously);
>   2. Run "lsusb -v" to find the vendorID and productID for the UPS;
>   3. "rmmod usbserial" if the module happens to be loaded already;
>   4. Load the module again with "modprobe usbserial vendor=0x...
> product=0x..." (or add this to your "/etc/modprobe.conf" file as
> "options usbserial vendor=0x... product=0x...");
>   5 .If there is now a "/dev/ttyUSBx" device available, configure
> "megatec" to use it.
> My Mustek PowerMust 600 doesn't have an USB interface, so I can't test
> this myself, and I have no idea if this works with some models, all
> models, or no models (*)...
> Anyone interested?
> (*) Or what happens if the usbserial driver gains successful control
> of a device that happens to be something else entirely not a
> usb-to-serial converter... Although I really doubt something bad would
> happen, I'm just covering my ass here... :)
> -- 
> Carlos Rodrigues
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