<?xml version="1.0" encoding="UTF-8" ?>
<?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>pls help...external interrupts 8051</title><link>https://community.arm.com/developer/tools-software/tools/f/keil-forum/22789/pls-help-external-interrupts-8051</link><description> 
i have used both the external interrupts ex0 and ex1 in the low
level triggered mode. whenever either interrupt occurs, the LED on
the output port is switched on, depending upon the input at pin
P3.2.if that is high the led should switch on,when it</description><dc:language>en-US</dc:language><generator>Telligent Community 10</generator><item><title>RE: pls help...external interrupts 8051</title><link>https://community.arm.com/thread/76610?ContentTypeID=1</link><pubDate>Mon, 25 Aug 2008 14:38:43 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:3e8cbedc-75b7-4299-9228-b91d6e66f520</guid><dc:creator>scrungy doolittle</dc:creator><description>&lt;p&gt;&lt;p&gt;
I think Erik meant that&lt;/p&gt;

&lt;p&gt;
if the pulse is to short, you will never see it as a 1.&lt;br /&gt;
Depending on the clock speed of your 8051, you may well be into the
interrupt after the signal has gone away.&lt;/p&gt;

&lt;p&gt;
there is a way to do this, but you have to burn both external
interrupts. You take your interrupt signal in, and run it through an
inverter and tie that to the other external interrupt. Program them
both for negative going edge sensitive interrupts. If the edge is a
falling one, you will get interupt 1 for example.&lt;br /&gt;
Since you know the edge was falling, and this is the non-inverted
interrupt, you know that the status of the pin is low. If you get the
other one, you know that the status of the pin would be high (the
inverter will cause a one or the other of these interrupts to happen
on every signal. The signal may go away, but by virtue of the fact
that you are in one interrupt or the other, you can figure that
out.&lt;/p&gt;

&lt;p&gt;
hope that helps.&lt;br /&gt;
Cheers&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item><item><title>RE: pls help...external interrupts 8051</title><link>https://community.arm.com/thread/52280?ContentTypeID=1</link><pubDate>Mon, 25 Aug 2008 05:30:18 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:98658b8b-fe73-4c81-bf69-8092dbf97434</guid><dc:creator>erik  malund</dc:creator><description>&lt;p&gt;&lt;p&gt;
&lt;i&gt;void ex0_isr (void) interrupt 0&lt;br /&gt;
{ if(a==1) //a is input bit at P3.2&lt;/i&gt;&lt;br /&gt;
if the pulse triggering the interrupt is not extremely short, a will
never be &amp;#39;1&amp;#39;&lt;/p&gt;

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