.. _qs-usb:

USB
===

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

The QS Computer-on-Modules, such as QSMP and QS8M, contain two separate 
USB 2.0 compliant interfaces. High-speed USB operates at 480 Mb/s observing 
some basic rules or guidelines will usually guarantee successful operation.

VBUS
----
The QS modules does not include a signal for supplying the 5V VBUS power 
for USB. An external power management chip or discrete logic for enabling 
VBUS is required for the host operation. The power distribution circuit must 
have over-current detection capability to be compliant with the USB standard.
There are no dedicated pins reserved for this in the QS standard.
Use General Purpose Input/Output (GPIO) pads as OE (VBUS_EN) and OC (VBUS_OC) 
for the VBUS power distribution circuit. Some QS modules have pins with 
dedicated VBUS_EN (Output) and VBUS_OC (Input) alternate functions, e.g. 
QS8M pin 71 - USB1_OTG_PWR and pin 72 USB1_OTG_OC. Using these may interfere 
with the use other standard QS interfaces. A switch designed specifically 
for USB power, such as the Maxim MAX1931, or a general purpose power-distribution 
chip, such as Micrel’s MIC2026, can be used.

.. note:: The i.MX8M Nano processor has only one integrated port.

+---------+------------+----------+---------+-----------------------------------+
| **Pin** | **Signal** | **type** | **I/O** | **Requirements**                  |
+---------+------------+----------+---------+-----------------------------------+
| 43      | USB_VBUS_A | 5V       | IN      | Can be connected to VBUS directly |
+---------+------------+----------+---------+-----------------------------------+
| 44      | USB_DN_A   | USB      | I/O     | Route USB differential signals    |
+---------+------------+----------+---------+ with 90 Ω differential impedance  +
| 45      | USB_DP_A   | USB      | I/O     |                                   |
+---------+------------+----------+---------+-----------------------------------+
| 46      | USB_VBUS_B | 5V       | IN      | Can be connected to VBUS directly |
+---------+------------+----------+---------+-----------------------------------+
| 47      | USB_DN_B   | USB      | I/O     | Route USB differential signals    |
+---------+------------+----------+---------+ with 90 Ω differential impedance  +
| 48      | USB_DP_B   | USB      | I/O     |                                   |
+---------+------------+----------+---------+-----------------------------------+

Wiring example
--------------

.. figure:: ../images/USB.png
   :alt:

.. rubric:: USB2.0 Design Recommendations

+-------------------------------------------------------+---------+---------+---------+
| **Parameter**                                         | **MIN** | **TYP** | **MAX** |
+-------------------------------------------------------+---------+---------+---------+
| Operating Speed                                       |         |         | 240 MHz |
+-------------------------------------------------------+---------+---------+---------+
| Signal Trace Length                                   |         |         |  15 cm  |      
+-------------------------------------------------------+---------+---------+---------+
| Differential Pair Skew                                |         |         |  5 ps   |
+-------------------------------------------------------+---------+---------+---------+
| Differential Trace Impedance                          |  81 Ω   |   90 Ω  |  99 Ω   |
+-------------------------------------------------------+---------+---------+---------+

.. _qs-usb3:

USB3 Super Speed
----------------

.. figure:: ../images/concept/qsx-pinout.png
   :width: 50%
   :figwidth: 50%
   :align: right
   :alt:

The QSXP provides a complete USB3.0 interface. To implement a 
USB Type-C interface (UFP, DFP, or DRP), external hardware 
must be added to manage the two configuration channel IOs 
(CC1 and CC2) as well as monitor the plug orientation and 
switch the single USB3 SS interface.

Route all USB differential signals with 90 Ω differential 
impedance.

+---------+------------+-----------------------------------+
| **Pin** | **Signal** | **Requirements**                  |
+---------+------------+-----------------------------------+
| 25A     | USB_TXN    |                                   |
+---------+------------+-----------------------------------+
| 26A     | USB_TXP    |                                   |
+---------+------------+-----------------------------------+
| 50A     | USB_RXN    |                                   |
+---------+------------+-----------------------------------+
| 51A     | USB_RXP    |                                   |
+---------+------------+-----------------------------------+

.. rubric:: USB3 Super Speed Design Recommendations

+-------------------------------------------------------+---------+---------+---------+
| **Parameter**                                         | **MIN** | **TYP** | **MAX** |
+-------------------------------------------------------+---------+---------+---------+
| Operating Speed                                       |         |         |  2.5 GHz|
+-------------------------------------------------------+---------+---------+---------+
| Signal Trace Length                                   |         |         |  10 cm  |      
+-------------------------------------------------------+---------+---------+---------+
| Differential Pair Skew                                |         |         |  1 ps   |
+-------------------------------------------------------+---------+---------+---------+
| RX/TX Skew                                            |         |         |  1.6 ns |
+-------------------------------------------------------+---------+---------+---------+
| Differential Trace Impedance                          |  85 Ω   |   90 Ω  |  95 Ω   |
+-------------------------------------------------------+---------+---------+---------+

.. rubric:: See also
   
`Texas Instruments High-Speed Interface Layout Guidelines <https://www.ti.com/lit/pdf/spracp4>`_
   
.. include:: index.rst