[Nut-upsuser] Server Does Not Shut Down - SOLVED!

Charles Lepple clepple at gmail.com
Tue Feb 28 02:19:25 UTC 2012

On Feb 27, 2012, at 5:25 PM, Steve Read wrote:

> I spent some time reading and thinking about your email and realized that normal (AC present, battery normal) is at -12V which is a logic low.
> I thought this was how I designed it but when I got funny results I convinced myself that it was +12V.

Of course, the mark/space terminology and weird logic levels on TXD/RXD don't help the debugging process.

I suppose this would also depend on fixing the ground pin, but if you're writing the microprocessor code yourself (and assuming you have a RS-232 line driver installed on the microprocessor board), one other thing to consider is emulating a "smart UPS". This would allow you to monitor voltages and whatnot. It also provides a more solid handshake between the UPS and the server - if the driver pings the UPS and it doesn't respond, you will get log messages.

The Megatec protocol has a simple ASCII query/response structure, and would be fairly easy to implement.


The "vendor" and "rating" strings can be constant, and the "status" is fixed-width fields - so it should be easy to implement even in assembly.

Then again, you might not be as obsessed with graphs and logs as I am :-)

Charles Lepple
clepple at gmail

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