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Voltage Signalling Features Supported by Apcupsd for Vari-
ous Cables
The following table shows the features supported by the current version
of apcupsd (3.8.5 or later) for various cables running the UPS in voltage-
signalling mode.
Cable Power Loss Low Battery Kill Power Cable Discon-
nected
940-0020B Yes No Yes No
940-0020C Yes Yes Yes No
940-0023A Yes No No No
940-0119A Yes Yes Yes No
940-0127A Yes Yes Yes No
940-0128A Yes Yes Yes No
940-0095A/B/C Yes Yes Yes No
simple Yes Yes Yes No
Voltage Signalling
Apparently, all APC voltage-signalling UPSes have the same signals on the
output pins of the UPS. The difference at the computer end is due to different
cable configurations. Thus, by measuring the connectivity of a cable, one
can determine how to program the UPS. This is to be verified.
The signals presented or accepted by the UPS on its DB9 connector using
the numbering scheme listed above is:
UPS Pin Signal meaning
1 <- Shutdown when set by computer for 1-5 seconds.
2 -> On battery power (this signal is normally low but
goes high when the UPS switches to batteries).
3 -> Mains down (line fail) See Note 1 below.
5 -> Low battery. See Note 1 below.
6 -> Inverse of mains down signal. See Note 2 below.
7 <- Turn on/off power (only on advanced UPSes only)
Note 1: these two lines are normally open, but close when the
appropriate signal is triggered. In fact, they are open collector
outputs which are rated for a maximum of +40VDC and 25 mA. Thus
the 4.7K ohm resistor used in the Custom Simple cable works
quite well.
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