USB-SD-Mux Overview

Theory Of Operation

The USB-SD-Mux multiplexes a micro SD card between a host and a Device under Test (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 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 DUT

+-------+     +--------------+     +-------+
|       |     |              |     |       |
|  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 DUT.

• The control software waits 1 second for the card to power down.

• The micro SD card data and power lines are 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 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 card to power down.

• The micro SD card is electrically multiplexed to the DUT connector on the USB-SD-Mux.

Electronics

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

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

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

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

This figures highlight the following aspects of the USB-SD-Mux:

1. The Mico-SD-Card shaped DUT connector of the USB-SD-Mux.

2. Three pairs of status LEDs (one each on the front and on the back):

   • 'DUT' and 'HOST' indicate which device the SD-Card is currently connected to.

   • A 'Power' LED that is on as long as the USB-SD-Mux is powered.

3. Micro SD card slot

4. Micro USB connector

5. (USB-SD-Mux FAST only) General purpose digital outputs