USB-SD-Mux Overview
###################

Theory Of Operation
-------------------

The USB-SD-Mux multiplexes a micro SD card between a host and a
Device under Test (:term:`DUT`).

The host is a computer that controls the operation of the
USB-SD-Mux and is able to access the micro SD card via USB.

The :term:`DUT` is the embedded board that you want to connect to a
Micro SD-Card.

The micro SD card is inserted into the card slot on the USB-SD-Mux.
The USB-SD-Mux is inserted into the micro SD card slot on the :term:`DUT`

.. code-block:: none

  +-------+     +--------------+     +-------+
  |       |     |              |     |       |
  |  DUT  +----->  USB-SD-Mux  <-----+ Host  |
  |       |     |              |     |       |
  +-------+     +------+-------+     +-------+
                       |
                       |
                +------v-------+
                |              |
                |   SD card    |
                |              |
                +--------------+

When the USB-SD-Mux is switched into host-mode using the control software
the following steps are executed:

* The micro SD card is electrically disconnected from the :term:`DUT`.
* The control software waits 1 second for the :term:`DUT` power down.
* The micro SD card is electrically multiplexed to the card reader on the
  USB-SD-Mux and the card-inserted signal on the card reader is toggled.
* The host system will detect that a micro SD card has been inserted into
  the USB-SD-Mux's card slot and start detection.
* On successful detection the card will be provided as a block device
  depending on your systems settings.

When the USB-SD-Mux is switched into :term:`DUT` mode using the control software
the following steps are executed:

* The micro SD card is electrically disconnected from the USB-SD-Mux' card reader.
* The control software waits 1 second for the :term:`DUT` power down.
* The micro SD card is electrically multiplexed to the :term:`DUT` connector on the
  USB-SD-Mux.


Electronics
-----------

The following figure shows a rendering of the USB-SD-Mux.

.. figure:: product-operation-overview.svg.png

   Front- and Back-View of the USB-SD-Mux

This figure shows the following areas:

(1) This area is the Mico-SD-Card shaped DUT connector of the USB-SD-Mux.
(2) Three status LEDs are arranged in this area:

    * 'DUT' and 'HOST' show to which side the SD card is multiplexed.
      If both LEDs off signal the SD card being disconnected.
    * The 3rd LED is active when the USB-SD-Mux is powered.

(3) micro SD card slot
(4) Micro USB connector