James, The unknown could be a way for the PC to tell the UPS to "shutdown". Just a guess!! Steve -----Original Message----- From: James Cameron [mailto:quozl@US.NETREK.ORG] Sent: Saturday, July 22, 2000 5:30 AM To: PICLIST@MITVMA.MIT.EDU Subject: [OT]: Help Wanted, UPS Interface G'day, I'm trying to figure out the interface pinout for a uninteruptible power supply (UPS) that I have. The unit came with no documentation, and no interface cable, and I suspect that the cable may require some pin remapping anyway. If you are willing to help, I've drafted a schematic of the circuit in the UPS attached to the DB9. I've not gone beyond the optocouplers; I got rapidly lost. I've also taken a few snapshots of the PCB. (220k of images) The UPS is straight analog; there are no digital components on the PCB, no crystals, no microcontrollers (sadly), just bog standard things like LM339's. I suspect therefore that the signalling from the UPS to the PC is just "online" and "low battery", via modem status lines. But there's a twist; there is an optocoupler facing the other direction. I can't figure out what function it has. -- James Cameron mailto:quozl@us.netrek.org http://quozl.netrek.org/ -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu