[Nut-upsuser] Server Does Not Shut Down

Charles Lepple clepple at gmail.com
Sun Feb 26 22:55:29 UTC 2012

On Feb 26, 2012, at 3:14 PM, Steve Read wrote:

> I made a simple device to apply either +12 or -12volts to both pin 1(DCD) and pin 8 (CTS) to help me understand the correct handshake but I am very confused.
> Here is a table of what I get:
> State	Pin 1	Pin 9	Note 		What I understand it means
> 1		+12V	+12V	OL			On Line - normal operation.
> 2		-12V	+12V	LB OL		I don't understand this. It should be On Battery.
> 3		+12V	-12V	OB			I thought this should be Low Battery.
> 4		-12V	-12V	OL			I thought the server should shut down?
> Note: results of running:
> /usr/local/ups/bin/upsc sdrups at localhost ups.status

For reference, here is the block for type=9 in genericups.h:

        /* Type 9 */
        { "APC",
          "APC Back-UPS (940-0023A cable)",
          0,                            /* cable power: none            */
          TIOCM_CD, 0,                  /* online: CD off               */
          TIOCM_CTS, TIOCM_CTS,         /* low battery: CTS on          */
          TIOCM_RTS                     /* shutdown: RTS                */

And the text from the genericups man page:

- - - - - - - - - -

9 = APC Back-UPS/Back-UPS Pro/Smart-UPS with 940-0023A cable

[CP=none] [OL=-DCD] [LB=CTS] [SD=RTS]

- - - - - - - - - -

For your tests where you apply voltage directly, CP is not relevant. (I assume your microcontroller provides its own power to the serial port control lines.) Also, SD=RTS is the shutdown signal *to* the UPS (saying that NUT acknowledges the UPS' low battery condition). But you mentioned pins 1 (DCD) and 8 (CTS), so we can ignore that for now.

The way I read this, online with a good battery should be negative voltages on both DCD and CTS. OB+LB should be positive voltages on both. On Battery (but not yet low) should be DCD high, CTS low. (The fourth condition could occur if the power has returned, but the battery has not yet charged.)

I am confused as to how you could get OL for both +/+ and -/- states. Your table says Pin 1 and Pin 9, but earlier you mention Pin 1 and Pin 8. Could pin 8 have been floating during the voltage test?

You can use statserial to double-check that your serial port hardware is still good.

Charles Lepple
clepple at gmail

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