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<?xml-stylesheet type="text/xsl" href="https://community.arm.com/utility/feedstylesheets/rss.xsl" media="screen"?><rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:slash="http://purl.org/rss/1.0/modules/slash/" xmlns:wfw="http://wellformedweb.org/CommentAPI/"><channel><title>MCB 2300 Schematics USB Softconnect</title><link>https://community.arm.com/developer/tools-software/tools/f/keil-forum/25102/mcb-2300-schematics-usb-softconnect</link><description> 
I am a bit confused about USB Softconnect. 

 
Is the circuitry to turn off the USB+ against 3.3 V resistor
mandatory ? Id like to simply tie a fixed resistor instead. Is that
possible? Are there any disadvantages to expect? 

 
What impedance is correct</description><dc:language>en-US</dc:language><generator>Telligent Community 10</generator><item><title>RE: MCB 2300 Schematics USB Softconnect</title><link>https://community.arm.com/thread/101693?ContentTypeID=1</link><pubDate>Sun, 08 Mar 2009 06:59:58 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:7b32e12f-5650-44d2-b237-bf3d1b50fef0</guid><dc:creator>Uli Behrenbeck</dc:creator><description>&lt;p&gt;&lt;p&gt;
Thanks Tsuneo, you&amp;#39;ve been such a help, as usual ;)&lt;/p&gt;

&lt;p&gt;
So I will fix the 1k5.&lt;/p&gt;

&lt;p&gt;
be well&lt;br /&gt;
Uli&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item><item><title>RE: MCB 2300 Schematics USB Softconnect</title><link>https://community.arm.com/thread/77231?ContentTypeID=1</link><pubDate>Fri, 06 Mar 2009 12:58:16 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:2e4b4e75-7421-433a-9ccc-728e2f7c3e1e</guid><dc:creator>Tsuneo Chinzei</dc:creator><description>&lt;p&gt;&lt;p&gt;
Ah, power-up delay is applied just for bus-powered device -
supplied power from USB VBUS.&lt;br /&gt;
Self-powered device doesn&amp;#39;t care of this delay.&lt;/p&gt;

&lt;p&gt;
Tsuneo&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item><item><title>RE: MCB 2300 Schematics USB Softconnect</title><link>https://community.arm.com/thread/55580?ContentTypeID=1</link><pubDate>Fri, 06 Mar 2009 12:42:25 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:7f09b976-4d6f-48ca-8729-29e16c0bb870</guid><dc:creator>Tsuneo Chinzei</dc:creator><description>&lt;p&gt;&lt;p&gt;
&lt;i&gt;&amp;quot;Is the circuitry to turn off the USB+ against 3.3 V resistor
mandatory ? Id like to simply tie a fixed resistor instead.&amp;quot;&lt;/i&gt;&lt;/p&gt;

&lt;p&gt;
For final product, the pull-up resistor to USB D+ (or D-) line can
be a fixed one.&lt;br /&gt;
But while development, the resistor should be switched by a MCU port
- soft attach/detach.&lt;/p&gt;

&lt;p&gt;
a) Power-up delay&lt;br /&gt;
Host PC (or hub) detects USB plug in by the D+ (or D-) line voltage
change. This pull-up resistor on the device side makes the voltage
change. With 100 ms (min) delay after plug in detection, host starts
enumeration sequence. Therefore within this period, your MCU should
finish its power-up initialization. If the initialization takes more
than 100 ms, soft attach should be used even for the final
product.&lt;/p&gt;

&lt;p&gt;
b) Disconnection by device&lt;br /&gt;
Soft attach/detach is used to disconnect/re-connect USB by the device
firmware, too. This function is often used for firmware update over
USB.&lt;/p&gt;

&lt;p&gt;
If your final product use neither power-up delay nor firmware
update, fixed pull-up will do.&lt;/p&gt;

&lt;p&gt;
While development, soft attach/detach is indispensable. Otherwise,
you have to plug off USB cable every time you reset the firmware.&lt;br /&gt;
&lt;br /&gt;
&lt;br /&gt;
&lt;br /&gt;
&lt;i&gt;&amp;quot;What impedance is correct, I found values between 800 and 1500
Ohm, so is 1200 the best choice?&amp;quot;&lt;/i&gt;&lt;/p&gt;

&lt;p&gt;
1k5 +/- 5%&lt;/p&gt;

&lt;p&gt;
New resistor_ecn.pdf has widened the tolerance. But to specify
resistor value for production, this old spec is better.&lt;/p&gt;

&lt;p&gt;
Tsuneo&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item></channel></rss>