Intended Use
############

Like 4DO's larger brother '3PO, who specialized in human cyborg relations,
the LXA IOBus 4DO-3DI-3AI is intended to facilitate interaction with other
electrical devices.

.. note::
  Do not use the LXA IOBus 4DO-3DI-3AI for any other use cases than the ones listed below.

The intended use cases are listed below:

* The LXA IOBus 4DO-3DI-3AI is intended to be used during the development of embedded
  devices to control and measure low-voltage and low-power signals.
  Using the LXA IOBus 4DO-3DI-3AI to control large voltages (>25V) or currents
  (>150mA) may damage the device.

* The LXA IOBus **4DO**\ -3DI-3AI exposes four digital output pins.
  These pins are implemented using galvanically isolated ``CPC1008N``
  solid-state relays.

  In the active output state the relays create an electrical connection
  between the output pins of a channel, that can be used to simulate
  a jumper being placed to the :term:`DUT`.

  In the inactive output state the relays present no electrical connection
  between the output pins of a channel.

* The LXA IOBus 4DO-**3DI**\ -3AI exposes three digital input pins.
  These pins are implemented using galvanically isolated ``CPC1008N``
  solid-state relays. These are driven by the :term:`DUT`.

  The inputs are electrically isolated from the rest of the board but
  share a common negative terminal. The inputs may optionally be isolated
  from one another by cutting marked traces on the :term:`PCB`.

  The inputs can handle voltages of up to 10V. The inputs are designed
  to indicate an active state for voltages above 1.8V.
  The inputs present an additional load to the :term:`DUT`.
  The approximate loads are as follows:

  * 0.5mA at 1.8V input voltage.
  * 4mA at 3.3V input voltage.
  * 8mA at 5V input voltage.
  * 20mA at 10V input voltage.

* The LXA IOBus 4DO-3DI-**3AI** exposes three analog input pins.
  These pins are connected directly to the on board microcontroller
  and share a common ``GND`` with the rest of the device and IOBus
  network.

  The analog input pins are designed to measure slowly-changing
  input voltages between 0V and 12V and present an approximate
  load of 19kΩ per input.

* The LXA IOBus 4DO-3DI-3AI is controlled using the LXA IOBus,
  a combined CAN-Bus and power interconnect.

* The LXA IOBus 4DO-3DI-3AI is intended to be controlled by a CANopen-inspired protocol
  via the `lxa-iobus-server`_. The server provides a web-based interface, as well
  as a :term:`REST`\ -based :term:`API`. The server allows controlling multiple
  IOBus devices on a bus.

.. warning::

   Make sure the voltage on the power input stays within the safe
   9V to 13V working range of the LXA IOBus 4DO-3DI-3AI.

.. _lxa-iobus-server: https://github.com/linux-automation/lxa-iobus/