.. _qs-sd:

SD Interface
================

Signals
-------

.. figure:: ../images/qs-pinout-sd.png
   :width: 50%
   :figwidth: 50%
   :align: right
   :alt:

+---------+------------+------------+---------+--------------------------------------+
| **Pin** | **Signal** | **type**   | **I/O** | **Description**                      |
+---------+------------+------------+---------+--------------------------------------+
| 36      | SD_CD      | 3V3        | I       | SD Card Detect – connected to a GPIO |
+---------+------------+------------+---------+--------------------------------------+
| 38      | SD_D0      | 3V3        | I/O     | SD Data bidirectional signals        |
+---------+------------+            +         +                                      +
| 37      | SD_D1      |            |         |                                      |
+---------+------------+            +         +                                      +
| 42      | SD_D2      |            |         |                                      |
+---------+------------+            +         +                                      +
| 41      | SD_D3      |            |         |                                      |
+---------+------------+------------+---------+--------------------------------------+
| 40      | SD_CMD     | 3V3        | I/O     | SD Command bidirectional signal      |
+---------+------------+------------+---------+--------------------------------------+
| 39      | SD_CLK     | 3V3        | O       | SD Output Clock.                     |
+---------+------------+------------+---------+--------------------------------------+

The QS standard pinout provides one dedicated SD interface.

SD-Card example diagram
-----------------------

Either the use of the processor internal pullups or the use of pullups on the baseboard is possible.

.. figure:: ../images/SD.png
   :alt:

.. rubric:: SDIO Design Recommendations

+-------------------------------------------------------+---------+---------+---------+
| **Parameter**                                         | **MIN** | **TYP** | **MAX** |
+-------------------------------------------------------+---------+---------+---------+
| Operating Speed (Ultra-High Speed SD, SDR104)         |         |         | 208 MHz |
+-------------------------------------------------------+---------+---------+---------+
| Operating Speed (MMCplus, eMMC)                       |         |         |  52 MHz |
+-------------------------------------------------------+---------+---------+---------+
| Signal Trace Length                                   |         |         |  10 cm  |      
+-------------------------------------------------------+---------+---------+---------+
| Data/Clock group skew (Ultra-High Speed SD, SDR104)   |         |         |  20 ps  |
+-------------------------------------------------------+---------+---------+---------+
| Data/Clock group skew (MMCplus, eMMC)                 |         |         | 100 ps  |
+-------------------------------------------------------+---------+---------+---------+
| Trace Impedance                                       |         |   50 Ω  |         |
+-------------------------------------------------------+---------+---------+---------+

   
.. include:: index.rst