nutdrv_siemens_sitop - driver for the Siemens SITOP UPS500 series UPS


nutdrv_siemens_sitop -h

nutdrv_siemens_sitop -a UPS_NAME [OPTIONS]

This man page only documents the hardware-specific features of the nutdrv_siemens_sitop driver. For information about the core driver, see nutupsdrv(8).


nutdrv_siemens_sitop supports Siemens UPS models from the SITOP UPS500 series. Some models have a serial port, others have a USB port. The models with USB port actually contain a serial-over-USB chip, so as far as this driver is concerned, all models are serial models. This driver should work with all models in the SITOP UPS500 series, as long as your kernel has support for the serial port device (see section USB driver below).

This driver has only been tested with the SITOP UPS500S-2.5 with USB port (Siemens product number 6EP1933-2EC41).


The UPS is configured via DIP-switches. For correct functioning in combination with NUT, set the DIP-switches to the following:

switch 1-4

Choose whatever suits your situation. Any combination will work with NUT.

switch 5 (⇒ / t)

Set to OFF (t). This ensures that the UPS will not cut power unless NUT tells it to do so (or unless the batteries are exhausted).

switch 6-10 (delay)

Set to OFF (minimum delay). Setting a higher delay will actually also work, but any command from NUT will be delayed as well before being executed by the UPS. With the minimum setting, it will already take 5 seconds before a command from NUT is executed.

switch 11 (INTERR.)

Set to ON (interrupt the output after the timer expires). This ensures that the UPS briefly interrupts the output power in response to the shutdown.return command. See the section Instant Commands below.

switch 12 (ON/OFF)

set to ON (enable the UPS functionality). Without this, the UPS will never supply power from its batteries.

USB driver

The USB-versions of the UPS contain an FTDI USB-to-serial converter chip. It is programmed with a non-standard product ID (for example 0403:e0e3), but can still be used with the normal ftdi_sio driver.

The following hints may be specific to GNU/Linux.

Use lsusb to figure out which product ID is used in your model, and replace all occurrences of e0e3 in the following examples with the actual Product ID.

modprobe ftdi_sio
echo 0403 e0e3 > /sys/bus/usb-serial/drivers/ftdi_sio/new_id

If your system uses udev, this can be automated via a udev rule:

ACTION=="add", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="e0e3", \
  RUN+="/sbin/modprobe ftdi_sio", \
  RUN+="/bin/sh -c 'echo 0403 e0e3 > /sys/bus/usb-serial/drivers/ftdi_sio/new_id'"

You can use the following udev rule to obtain a predictable device name, for example /dev/ttyUPS:

SUBSYSTEM=="tty" ATTRS{idVendor}=="0403", ATTRS{idProduct}=="e0e3" SYMLINK+="ttyUPS"


The UPS does not have a special get status command. Instead, it continuously sends out status update messages (tens of messages per second). Every pollinterval, these messages are read from the serial port buffer.

In order to react quickly on status changes from the UPS, and to prevent the serial buffer from overflowing, pollinterval should be set to a relatively low value. The recommended value is 1 (second).


This driver supports the following optional settings:


The serial port is polled periodically for new data (see Polling). If there is no valid new data after num polls, it is assumed that communication with the UPS is lost. The default value is 2. Lower values may cause spurious Data stale messages, especially at startup.



The behavior of this command depends on the line state:

  • on line: after 5 seconds (or longer, if DIP switches 6-10 are not OFF), the UPS will shut off its output. After another 5 seconds, the output is activated again.

  • on battery: after 5 seconds (or longer, if DIP switches 6-10 are not OFF), the UPS will shut off its output. The output will stay off, until the line voltage has returned.


The behavior of this command depends on the line state:

  • on line: after 5 seconds (or longer, if DIP switches 6-10 are not OFF), the UPS will shut off its output. The output stays off, until the line voltage has been removed for at least 1 second, and has been re-applied.

  • on battery: this command behaves the same as shutdown.return.


Make sure that your operating system has created a serial device for the UPS. See the section USB driver for more information.

Next, make sure that NUT has access rights to this device file. For example, by creating a udev rule that grants permission to the NUT user, or by adding the NUT user to a user group that can access serial devices (e.g. the dialout group on Debian-based systems).


You can verify the correct functioning of the hardware, by monitoring the serial port with a terminal program, for example picocom:

picocom -b 9600 -d 8 -p n /dev/ttyUPS

NUT must not be running when you do this. You should now see a continuous stream of 5-character texts coming in, for example:


To exit picocom, use Ctrl-A Ctrl-X.


Untested models

As mentioned under Supported hardware, this driver has not been tested with all models in the SITOP UPS500 series.

Data stale messages

The firmware in these UPSes is quite buggy. After sending data to the UPS, it sometimes stops sending status updates. This driver tries to prevent this (e.g. by sending commands twice, and by sending additional LF characters after each command). Once the UPS is in this state, communication can only be restored by rebooting the UPS, or by unplugging and reconnecting the USB cable. During normal operation, no commands are sent to the UPS at all (only at shutdown), so this issue is expected to have little impact on usability. It is not sure if the serial models are affected by this issue as well.


Matthijs H. ten Berge


The core driver:

Internet resources:

The NUT (Network UPS Tools) home page: