[Nut-upsuser] Unitek iZi UPS 525

Arjen de Korte nut+users at de-korte.org
Tue Dec 26 11:04:06 CET 2006

> Really? Silly me then; Megatec looked like a fairly evolved protocol so I
> was afraid that, since no RTS/CTS signaling was in place into the
> manufacturer supplied cable, maybe plain RX/TX/GND won't do. For example
> Minicom showed "Offline" all the time during the tests.

Most (if not all) smart protocols only use RX/TX for communication. If
other pins are used (DTR and RTS) they are usually used for powering the
PC side of the serial interface. Hardware handshaking is seldomly used at
these slow speeds (1200/2400 baud) and not needed anyway. Only when you're
running at significantly higher speeds and risk buffer overflows if the
processing can't keep up with the data flow, you might need some form of
flow control. But in that case, XON/XOFF (software) flow control, works
just as good as RTS/CTS (hardware) flow control. Usually, manufacturers
just don't want to spend the additional hardware (opto-isolators for
instance) required to do the latter.

>> The compatibility list you're referring to is outdated. There
>> have been quite some changes recently (also in the new
>> megatec driver)
> ... :-D Good to know. Last night I've ended up soldering all but one of
> the cables listed in the "Cables" page of NUT just to discover that it
> wasn't the cable, it was simply the driver.

Oops! If a cable is supplied with the UPS, you should be using that. Only
if you don't have a cable, you could try making one yourself. This is also
somewhere in the documentation, but you already found out the hard way.

> Note to anyone Googling for Unitek iZi UPS 525 and Linux: it's a Mustek
> UPS and at least with NUT 2.0.3 it works with "powermust" driver using the
> supplied cable.

Note that powermust has also been replaced by megatec in nut-2.0.5.

> Missing the cable? It's a simple straight RX/TX/GND; on
> DB9:
> 2->2, 3->3, 5->5. Before doing any tests with NUT make sure you can
> communicate with the UPS using Minicom: go for 2400 8N1, turn hardware
> flow control off and issue a Q1 command, UPS should answer with a "(value
> value value..." type of string.

Sound advice.

>> and nut-2.0.5 will be released in just a
>> couple days from now. If you can't wait for that, grab it
>> from the SVN trunk.
> 2.0.3 is biting me bad in the upssched department so I guess I'll have to
> go for SVN. :-(

Like how? There have not been too many major bugs in upssched and as far
as I know this has not changed significantly (if at all) since nut-2.0.3.
Could you please describe what is not working for you here? This may be
just a configuration error or something more sinister which requires work
from the developers.

Best regards, Arjen
Eindhoven - The Netherlands
Key fingerprint - 66 4E 03 2C 9D B5 CB 9B  7A FE 7E C1 EE 88 BC 57

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