Subject: UPS RS232 cabling question
To: None <current-users@NetBSD.ORG>
From: VaX#n8 <>
List: current-users
Date: 05/04/1997 03:15:36
Heya.  I'm trying to set up a UPS to PC, RS232 connection.
I've got two signals coming in (wall power out, and battery low), and
one going out (shutdown).  Any suggestions on which signals to use?
Which one should hook up to carrier detect (DCD)? (I think wall power out).
I have a RS232 spec with the directions of the signals; I'm looking for
something more than that, like advice from someone who has done it.
Last time I tried to drive the serial control lines from NetBSD, it
didn't work too well.
Also, the UPS signals the computer by pulling it's output lines to signal
ground via an optoisolator, with the signal coming in the collector.
Will that draw the levels logically high?  Will it be sufficient
to interface with a normal RS-232 serial connector on the PC?
When it is not signalling, the UPS lets them float.  e.g.

---+     +------- power low pin
   |  /  |c
   V  / bO   (NPN xistor)
   -  /  |e
   |     |
---+     +------- signal ground

(yes, they really did draw the "light rays" going the wrong way,
 with the arrow heads pointing at the diode, and they forgot to label
 one of the optoisolators in the English version of the diagram;
 luckily I can read Spanish...
 I think they should put these diagrams on the web...)

This is an Exide One-UPS 1200 VA btw.
I believe it is discontinued but the price was right.

Also, the shutdown signal is pretty weird; the diagram shows an
arrow pointing toward the signal pin, labelled "1 MIN >= 3.3mA"
and there is a "computer shutdown signal" from whose positive
terminal that signal leaves, and it has a blowup of a V vs time
pulse diagram, with the peak 5V or 12V, and the width 30ms.
I am not sure if the transition back to zero shuts the UPS off,
or if the initial transition to 5-12V shuts it off after a 30ms

Also, the thermistor on the UPS seems to keep the fan on for a while,
kick off briefly, kick on briefly, then shut off (with a relay's audible
CLICK) for a good period of time.

Your help is appreciated.

PS: I recently found out that these mailing lists are gatewayed to a
    (non-local?) usenet group and therefore end up on DejaNews...
VaX#n8 | |
League of Non-aligned Wizards | amateur solder gunslinger