Network UPS Tools: APC's smart protocol

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APC's smart protocol

Description

Here's the information on the elusive APC smart signalling protocol used by their higher end units (Back-UPS Pro, Smart-UPS, Matrix-UPS, etc). What you see here has been collected from a variety of sources. Some people analyzed the chatter between PowerChute and their hardware. Others sent various characters to the UPS and figured out what the results meant.

RS-232 differences

Normal 9 pin serial connections have TxD on 3 and RxD on 2. APC's smart serial ports put TxD on pin 1 and RxD on pin 2. This means you go nowhere if you use a normal straight through serial cable. In fact, you might even power down the load if you plug one of those cables in. This is due to the odd routing of pins - DTR and RTS from the PC usually wind up driving the on/off line. So, when you open the port, they go high and *poof* your computer dies.

Originally this evil hack was used to connect the UPS to the PC when this page was first being built. As you can see, I cheated and neglected the ground (only 2 wires!) and it still worked. This method can be used for playing around, but for professional systems this is obviously not a viable option.

That hack didn't work out so well (damned cats), so it was retired quite awhile back. The most practical solution was to go out and BUY the DOS/Win version of Powerchute just for the black (smart) cable. I recommend doing the same thing if you actually care about this thing working properly. Of course, if you have one of the newer packages that came with PowerChute, you already have the cable you need.

Cable hacking

Redrawn 940-0024C clone diagram (D. Stimits)
Mac 940-0024C clone diagram (Miguel Howard)
Original 940-0024C diagram (Steve Draper)

If you are handy with cable tools, check out these diagrams. They show how to clone the black "smart" cable that's normally provided with APC models sold after 1996. The loopback pins (back to the PC) are used to keep PowerChute happy by allowing cable detection. If you use the NUT apcsmart or newapc drivers, those pins don't matter.

The Smart Protocol

Despite the lack of official information from APC, this table has been constructed. It's standard RS-232 serial communications at 2400 bps/8N1. Don't rush the UPS while transmitting or it may stop talking to you. This isn't a problem with the normal single character queries, but it really does matter for multi-char things like "@000". Sprinkle a few calls to usleep() in your code and everything will work a lot better.

Character	Meaning	Typical results	Other info
^A	Model string	SMART-UPS 700	Spotty support for this query on older models
^N	Turn on UPS	n/a	Send twice with > 1.5s delay between chars Only on 3rd gen SmartUPS and Black Back-UPS Pros
^Z	Capability string	(long string)	See "Capabilities" section for more info
A	Front panel test	Light show + "OK"	Also sounds the beeper for 2 seconds
B	Battery voltage	27.87	This obviously varies a lot based on the current charge. Compare this to the nominal battery voltage
C	Internal temperature	036.0	Units are degrees C
D	Runtime calibration	!, then $	Runs until battery is below 25% (35% for Matrix) This updates the 'j' values - only works at 100% battery charge Can be aborted with a second "D"
E	Automatic selftest intervals	336	Writable variable Values: 336 (14 days) 168 (7 days) ON (at power on) (note extra space) OFF (never)
F	Line frequency, Hz	60.00	If this varies much, have a word with your local electrician
G	Cause of transfer	O	Writable variable Values: R (unacceptable utility voltage rate of change) H (high utility voltage) L (low utility voltage) T (line voltage notch or spike) O (no transfers yet since turnon) S (transfer due to U command or activation of UPS test)
I	Measure-UPS Alarm enable	FF	(not yet decoded)(bitmapped table, coming soon)
J	Measure-UPS Alarm status	0F,00	(not yet decoded)(bitmapped table, coming soon)
K	Shutdown with grace period	OK	Send twice with > 1.5s delay between chars Older units may send "*" instead of "OK" Also see grace period
L	Input line voltage	118.3	Does not necessarily read 000.0 on line failure
M	Maximum line voltage	118.9	This is the max voltage since the last time this query was run
N	Minimum line voltage	118.9	Like the one above, this one also resets itself on every query
O	Output voltage	118.3	Also see on battery output voltage
P	Power load %	023.5	Relative to the capacity of the UPS
Q	Status flags	08	See status flags section for more info
R	Turn dumb	BYE	Only on 3rd gen Smart-UPS, Smart-UPS v/s, Back-UPS Pro UPS must receive command to enter smart mode continue communications after sending this
S	Soft shutdown	OK	Command executes after grace period UPS goes online when power returns Only works when on battery
U	Simulate power failure	!, then $	See async notifier section for info on ! and $
V	Firmware revision	GWD	Can be used to determine abilities of hardware
W	Self test	OK	Tests battery, like pushing the test button on the front panel Also see test results entry
X	Self-test results	OK	Values: OK - good battery BT - failed due to insufficient capacity NG - failed due to overload NO - no results available (no test performed in last 5 minutes)
Y	Enter smart mode	SM	This must be sent before anything else on this page will work. Also see turn dumb command to exit smart mode
Z	Shutdown immediately	n/a	Send twice with > 1.5s delay between chars UPS switches the load off immediately (no grace period)
a	Protocol info	(long string)	Returns three main sections: Protocol version Alert messages (aka async notifiers) Valid commands Sections are separated with a period
b	Firmware revision	50.9.D	Decoding above info: 50 = SKU (variable length) 9 = firmware revision D = country code (used in capability decoding)
c	UPS local id	UPS_IDEN	Writable variable Up to 8 letter identifier for keeping track of your hardware
e	Return threshold	00	Writable variable Minimum battery charge % to return from shutdown after power returns Values: 00 = 0% (UPS switches on immediately) 01 = 15% 02 = 25% 03 = 90% This prevents excessive cycling during multiple power failures
g	Nominal battery voltage	024	The battery voltage that's expected to be present in the UPS normally Compare to the actual voltage reading
f	Battery level	099.0	Percentage It's much easier to use this rather than doing math on the current battery voltage and the nominal battery voltage
h	Measure-UPS Ambient humidity	042.4	Percentage Only works on models with the Measure-UPS SmartSlot card
i	Measure-UPS Dry contacts	00	Bitmapped hex variable Component values: 10 = contact 1 20 = contact 2 40 = contact 3 80 = contact 4
j	Estimated runtime	0327:	Minutes Must be calibrated to be effective
k	Alarm delay	0	Writable variable Values: 0 = 5 second delay after power failure T = 30 second delay L = alarm at low battery only N = alarm disabled Does not affect low battery warning
l	Low transfer voltage	103	Writable variable See capabilities to get values for a UPS UPS goes on battery after voltage drops below this point
m	Manufacturing date	11/29/96	Format may vary by country (MM/DD/YY vs DD/MM/YY)
n	Serial number	WS9643050926	Unique for each UPS
o	On-battery voltage	115	May be a writable variable on 220/230/240 VAC units
p	Shutdown grace delay	020	Writable variable - seconds See capabilities to read values Sets the delay before soft shutdown completes
q	Low battery warning	02	Writable variable - minutes See capabilities to read values The UPS will report a low battery this many minutes before it runs out of power
r	Wakeup delay	000	Writable variable - seconds See capabilities to read values The UPS will wait this many seconds after reaching the minimum charge before returning online
s	Sensitivity	H	Writable variable See capabilities to read values Meaning of values: H - highest M - medium L - lowest A - autoadjust (Matrix only)
u	Upper transfer voltage	132	Writable variable See capabilities to read values UPS goes on battery after voltage rises above this poiont
v	Measure-UPS Firmware	4Kx	Firmware information for Measure-UPS board
t	Measure-UPS Ambient temperature	80.5	Degrees C Only works on models with the Measure-UPS SmartSlot card
x	Last battery change	11/29/96	Writable variable This holds whatever the user sets in it, much like the UPS local id variable
y	Copyright notice	(C) APCC	Only works if firmware letter is later than O
z	Reset to factory settings	CLEAR	Resets most variables to initial factory values except identity or battery change date Not on SmartUPS v/s or BackUPS Pro
-	Capability cycle	(various)	Cycle through possible capability values UPS sends \| afterward to confirm change to PROM
@nnn	Shutdown and return	OK	UPS shuts down after grace period with delayed wakeup after nnn tenths of an hour plus any wakeup delay time Some older models send * instead of OK
0x7f	Abort shutdown	OK	Abort shutdown - use to abort @, S, K Also known as the delete key in some places
~	Register #1	n/a	See register 1 table
'	Register #2	n/a	See register 2 table
7	Dip switch positions	n/a	See dip switch table Only makes sense on models which actually have dip switches
8	Register #3	n/a	See register 3 table
9	Line quality	FF	Values 00 - unacceptable FF - acceptable
>	Battery packs	n/a	SmartCell models: returns number of connected packs Non-SmartCell models: returns number set by user (use + and -)
[	Measure-UPS Upper temp limit	NO,NO	Degrees C Writable variable Values: 55,50,45,...,05 for both Use - to enumerate through left side, + to enumerate through right side
]	Measure-UPS Lower temp limit	NO,NO	Degrees C Writeable variable See 'lower temp limit' above
{	Measure-UPS Upper humidity limit	NO,NO	% Writable variable Values: 90,80,70,...,10 for both Use - and + to change values
}	Measure-UPS Lower humidity limit	NO,NO	% Writable variable Values: 90,80,70,...,10 for both Use - and + to change values
Matrix-UPS and Symmetra commands
^	Run in bypass mode	n/a	If online, "BYP" response is received as bypass mode starts If already in bypass, "INV" is received and UPS goes online If UPS can't transfer, "ERR" received
<	Number of bad battery packs	000	Returns count of bad packs connected to the UPS
/	Load current	n/a	True RMS load current drawn by UPS
\	Apparent load power	n/a	Output load as percentage of full rated load
^V	Output voltage selection	n/a	Writable variable Values: A - Automatic (based on input tap) M - 208 VAC I - 240 VAC
^L	Front panel language	n/a	Writable variable Values: E - English F - French G - German S - Spanish Also 1, 2, 3, 4 - unknown
w	Run time conservation	n/a	Writable variable Values: NO - disabled 02 - leave 2 minutes of runtime in battery 05 - leave 5 minutes 08 - leave 8 minutes

Dip switch information

Bit	Switch	Option when bit=1
0	4	Low battery alarm changed from 2 to 5 mins. Autostartup disabled on SU370ci and 400
1	3	Audible alarm delayed 30 seconds
2	2	Output transfer set to 115 VAC (from 120 VAC) or to 240 VAC (from 230 VAC)
3	1	UPS desensitized - input voltage range expanded
4-7	-	Unused at this time

Status flags

Some common things you'll see:

08 = on line, battery OK
10 = on battery, battery OK
50 = on battery, battery low

Bit	Meaning
0	1 = runtime calibration occurring Not reported by Smart UPS v/s and BackUPS Pro
1	1 = SmartTrim Not reported by 1st and 2nd generation SmartUPS models
2	1 = SmartBoost
3	1 = on line
4	1 = on battery
5	1 = overloaded output
6	1 = battery low
7	1 = replace battery

Alert messages

Character	Description
!	Line Fail - sent when the UPS goes on-battery, repeated every 30 seconds until low battery condition reached. Sometimes occurs more than once in the first 30 seconds.
$	Return from line fail - UPS back on line power, only sent if a ! has been sent.
%	Low battery - Sent to indicate low battery, but not on SmartUPS v/s or BackUPS Pro models
+	Return from low battery - Sent when the battery has been recharged to some level only if a % has been sent previously
?	Abnormal condition - sent for conditions such as "shutdown due to overload" or "shutdown due to low battery capacity". Also occurs within 10 minutes of turnon.
=	Return from abnormal condition - Sent when the UPS returns from an abnormal condition where ? was sent, but not a turn-on. Not implemented on SmartUPS v/s or BackUPS Pro models.
*	About to turn off - Sent when the UPS is about to switch off the load. No commands are processed after this character is sent. Not implemented on SmartUPS v/s, BackUPS Pro, or 3rd generation SmartUPS models.
#	Replace battery - Sent when the UPS detects that the battery needs to be replaced. Sent every 5 hours until a new battery test is run or the UPS is shut off. Not implemented on SmartUPS v/s or BackUPS Pro models.
&	Check alarm register for fault (Measure-UPS) - sent to signal that temp or humidity out of set limits. Also sent when one of the contact closures changes states. Sent every 2 minutes, stops when the alarm conditions are reset. Only sent for alarms enabled with I. Cause of alarm may be determined with J. Not on SmartUPS v/s or BackUPS Pro.
\|	Variable change in EEPROM - Sent whenever any EEPROM variable is changed. Only supported on Matrix UPS and 3rd generation SmartUPS models.

Register 1

All bits are valid on the Matrix UPS. SmartUPS models only support bits 6 and 7. Other models do not respond.

Bit	Meaning
0	In wakeup mode (typically lasts < 2s)
1	In bypass mode due to internal fault - see register 2 or 3
2	Going to bypass mode due to command
3	In bypass mode due to command
4	Returning from bypass mode
5	In bypass mode due to manual bypass control
6	Ready to power load on user command
7	Ready to power load on user command or return of line power

Register 2

Matrix UPS models report bits 0-5. SmartUPS models only support bits 4 and 6. SmartUPS v/s and BackUPS Pro report bits 4, 6, 7. Unused bits are set to 0. Other models do not respond.

Bit	Meaning
0	Fan failure in electronics, UPS in bypass
1	Fan failure in isolation unit
2	Bypass supply failure
3	Output voltage select failure, UPS in bypass
4	DC imbalance, UPS in bypass
5	Command sent to stop bypass with no battery connected - UPS still in bypass
6	Relay fault in SmartTrim or SmartBoost
7	Bad output voltage

Register 3

All bits are valid on the Matrix UPS and 3rd generation SmartUPS models. SmartUPS v/s and BackUPS Pro models report bits 0-5. All others report 0-4. State change of bits 1,2,5,6,7 are reported asynchronously with ? and = messages.

Bit	Meaning
0	Output unpowered due to shutdown by low battery
1	Unable to transfer to battery due to overload
2	Main relay malfunction - UPS turned off
3	In sleep mode from @ (maybe others)
4	In shutdown mode from S
5	Battery charger failure
6	Bypass relay malfunction
7	Normal operating temperature exceeded

Capabilities

Upon sending a ^Z, your UPS will probably spit back something like this (truncated here for the example):

#uD43132135138129uM43229234239224uA43110112114108 ....

It looks bizarre and ugly, but is easily parsed. The # is some kind of marker/ident character. Skip it. The rest fits this form:

Command character - use this to select the value
Locale - use 'b' to find out what yours is, '4' applies to all
Number of choices - '4' means there are 4 possibilities coming up
Choice length - '3' means they are all 3 chars long

Then it's followed by the choices, and it starts over.

Matrix-UPS models have ## between each grouping for some reason.

Acknowledgements

Large parts of this data were contributed or corrected by Steven Freed. This guy is some sort of APC UPS god. Many thanks.

Last updated: 29 October 2003 / rkroll