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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>Using P0 port for driving +3.3 V Devices</title><link>https://community.arm.com/developer/tools-software/tools/f/keil-forum/27658/using-p0-port-for-driving-3-3-v-devices</link><description> 
Hello, 

 
I have a question. Can we use P0 port of 8051 for I/O of an
external device which has +3.3V ratings for its I/O? 

 
Thanks 
 </description><dc:language>en-US</dc:language><generator>Telligent Community 10</generator><item><title>RE: Using P0 port for driving +3.3 V Devices</title><link>https://community.arm.com/thread/116280?ContentTypeID=1</link><pubDate>Mon, 07 Mar 2011 08:50:53 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:11813691-cda9-4e94-95fd-ee25d246f1d3</guid><dc:creator>R Narasimha Swamy</dc:creator><description>&lt;p&gt;&lt;p&gt;
Thanks for the information.&lt;/p&gt;

&lt;p&gt;
With regards&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item><item><title>RE: Using P0 port for driving +3.3 V Devices</title><link>https://community.arm.com/thread/104656?ContentTypeID=1</link><pubDate>Mon, 07 Mar 2011 06:37:37 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:378742d7-63f3-4342-aecd-b4a3c8a1932b</guid><dc:creator>&amp;#178;erik malund</dc:creator><description>&lt;p&gt;&lt;p&gt;
for most (and I believe the AT89S52 - check the datasheet) old
fashioned &amp;#39;51 derivatives P0 is &amp;#39;open drain&amp;#39; which means that there
is no pullup on the pins. Thus if you pull up with resistors
connected to 3V3 this will, for output be a 3V3 bus. For input to PO
you will have to check the output range (Voh Vol) of your other chip
vs the input range of (Vih Vil) the AT chip and beware that you
maintain a decent noise margin.&lt;/p&gt;

&lt;p&gt;
Erik&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item><item><title>RE: Using P0 port for driving +3.3 V Devices</title><link>https://community.arm.com/thread/79091?ContentTypeID=1</link><pubDate>Sun, 06 Mar 2011 20:44:00 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:ffca79fe-4c75-4bdd-87c2-3cd16b6283b1</guid><dc:creator>Narasimha Swamy</dc:creator><description>&lt;p&gt;&lt;p&gt;
Hello,&lt;/p&gt;

&lt;p&gt;
Thanks for the prompt reply.&lt;/p&gt;

&lt;p&gt;
Sorry for the incomplete information. The details are as
follows.&lt;/p&gt;

&lt;p&gt;
The Controller is Atmel make AT89S52, 8 bit micro controller with
4K bytes of in system programmable flash. This controller is
compabile with industry standard 8051 for general functions and IO
pins.&lt;/p&gt;

&lt;p&gt;
The control functionality we are proposing is two way for the same
port i.e it will be used as write as well as read pin for sending the
command and acquiring the data from same port.&lt;/p&gt;

&lt;p&gt;
With regards&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item><item><title>RE: Using P0 port for driving +3.3 V Devices</title><link>https://community.arm.com/thread/66359?ContentTypeID=1</link><pubDate>Sun, 06 Mar 2011 01:24:31 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:b603a3c3-1398-472b-a629-daa54c603ee1</guid><dc:creator>ImPer Westermark</dc:creator><description>&lt;p&gt;&lt;p&gt;
I have a question. Don&amp;#39;t you think it would be relevant to specify
exactly what 8051 chip you have, since there are thousands and
thousands of different manufacturers and models available?&lt;/p&gt;

&lt;p&gt;
In the general case, the answer is no. But the datasheet for your
specific chip can tell you what voltage levels the pin inputs
requires to be safely detected as high or low. And the datasheet for
your 3.3V device will tell what voltages it emits as high or low.&lt;/p&gt;

&lt;p&gt;
In the other direction, where the 8051 pin is output, it depends a
lot on if your specific chip have a pseudo output with a pull-up to
3.3V or if it forcibly drives the signal to +5V. And it depends a lot
on if the external hardware is 5V tolerant - some 3.3V chips have
5V-tolerant inputs, i.e. output signals swings between 0 an 3.3V
while inputs are detected as low or high in the 3.3V range but
allowed to be drawn to 5V without problems.&lt;/p&gt;

&lt;p&gt;
Without more information from you, we can&amp;#39;t really help you but
tell you to read the datasheets. You might have to add resistors or
level converters between the two chips. But your didn&amp;#39;t even spent
the time to tell your signal directions.&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item></channel></rss>