Jim Lux wrote: >(with the icky aspect of some UPSes > requiring active voltage to shut them down.. WHAT were they thinking?)
No kidding. Not only that, but when dealing with these UPS interfaces a degree in mind reading and reverse engineering is required, since the companies never publish full specs for the wiring on these ports. The APC unit in the room provides its own 24V (more or less) on one pin of the serial interface. That's convenient. What isn't convenient is if you use their little EPO adapter the UPS can't run "SMART" anymore (according to their tech support). So you lose the ability to carry on most types of data transfer with the unit. Instead it goes to "simple" (contact closure) mode. The APC has two different shutdown pins, one causes it to send a shutdown command to the attached PC, hang around a while, and then turn itself off. The other is an EPO appropriate "turn off instantly". Now the "SMART" cable doesn't actually use the EPO pin, or the DC pin, so one could wire in an adapter between the SMART cable and the UPS that would conditionally pull the poweroff line up without affecting the normal "SMART" operation. Except, APC tells me this is an "unsupported" mode of operation. One has to wonder why they didn't do it that way themselves, so that their adapter could retain "SMART" operation. The TrippLite that takes a Y adapter cable is even more interesting. The specs for that cable say that one need only short the center two RJ11 pins to kill the inverter. Yet from everything we know about that interface, the inverter kill line must be pulled high in order to kill the inverter. So yesterday I measured the voltages on all the serial port pins, and guess what, there's no significant positive voltage in there. There is however -6.5V on one pin, so maybe the kill works if that pin is pulled below ground as well? The only way to find out what that cable is really doing is to buy one and analyze it. Personally I find the way the UPS companies hide information about the interface jacks on their UPS units to be super annoying. There isn't enough engineering info available to make reasonable design decisions about what you're going to hook up to them, unless it's just the one computer to the one UPS, in which case the cable that came with the unit is fine. Simple nontechnical instructions like "short these pins" don't tell me enough to know what all the valid options are. For instance, could an opto-isolator go in there? What will the voltage be across those pins before it is shorted? What is a "short" in this context: 0.1 Ohm, 10 Ohm, 1000 Ohm? How much current could flow when the pins are shorted? Little bitty relays can sometimes be welded shut by pretty small currents. How much current must flow for the unit to turn off? As things stand now the only safe thing to do is to put a pretty big physical contact switch (perhaps relay driven) on it and hope they've designed things so that the RJ11 pins don't melt in the jack when the switch is thrown. Either that or I have to spend time experimenting with the interface, plugging in resistors, measuring voltages or currents - none of which should be necessary. Regards, David Mathog [EMAIL PROTECTED] Manager, Sequence Analysis Facility, Biology Division, Caltech _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
