David Dyer-Bennet wrote: <snip> > Note that my two UPSs use "stupid" communications protocol, not > "smart". There's actually a diagram in the Back-ups 600 manual > showing what each connection on the 9-pin port is (I believe from > reading how-tos and things that they 600 and 650 are about the same in > this; the 650 manual doesn't actually give a diagram, though). > > The diagram actually looks like it would be better off with a pull-up > resistor on the line it uses to signal line power fail (the 600 > manual, at least, describes that line and two others as open-collector > outputs). It seems like apples and oranges here. Sounds like the ups's are discrete type outputs (open collector) designed to run an external alarm, and you want to hook it to a serial port. Won't work. Some ups's are switchable between serial and discrete (stupid) outputs. Or maybe some pins are for serial and others are alarm outputs. Best ups did this for a while. If you can set it for serial try a null modem adapter or cable. John