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<concept id="GUID-DA8526FB-5789-4CB6-9A92-754E39C52E3B" xml:lang="en"><title>Pin
Direction Functions</title><shortdesc>Describes the pin direction functions involved in implementing
the Symbian platform GPIO class.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>Pins are used as inputs or outputs of binary signals. The Symbian platform
GPIO class does not support bidirectional pins. However, some platforms allow
pins to be in a quiescent state (also called floating or tri-stated). In this
case a pin can be in one of three logical states namely, True, False or quiescent
as specified in the enumeration <codeph>TGpioDirection</codeph>. The relevant
three-valued logic is specified in this table.</p>
<table id="GUID-C656B1CE-149D-4BCA-94BD-7B906E93F173">
<tgroup cols="3"><colspec colname="col1"/><colspec colname="col2"/><colspec colname="col3"/>
<thead>
<row>
<entry nameend="col2" namest="col1" valign="top"><p>Input </p> </entry>
<entry valign="top"><p>Output</p></entry>
</row>
</thead>
<tbody>
<row>
<entry><p>A</p></entry>
<entry><p>B</p></entry>
<entry><p>C</p></entry>
</row>
<row>
<entry><p>0</p></entry>
<entry><p>0</p></entry>
<entry><p>Z</p></entry>
</row>
<row>
<entry><p>1</p></entry>
<entry><p>0</p></entry>
<entry><p>Z</p></entry>
</row>
<row>
<entry><p>0</p></entry>
<entry><p>1</p></entry>
<entry><p>0</p></entry>
</row>
<row>
<entry><p>1</p></entry>
<entry><p>1</p></entry>
<entry><p>1</p></entry>
</row>
</tbody>
</tgroup>
</table>
<section id="GUID-3DA1E4AC-BAE0-469E-8A5D-72E292A533C1"><title>Implement the
pin direction functions</title> <ul>
<li><p>          Implement <xref href="GUID-38FAAC57-13CF-390F-AE05-8D2B9E092450.dita"><apiname>SetPinDirection()</apiname></xref> for each value
         of the enumeration <xref href="GUID-2F6DB4C0-D198-39A8-B990-EF1D5B9B5901.dita"><apiname>TGpioDirection</apiname></xref>.</p><ul>
<li><p>             Implement <xref href="GUID-38FAAC57-13CF-390F-AE05-8D2B9E092450.dita"><apiname>SetPinDirection()</apiname></xref> with  
          <codeph>aDirection</codeph> == <xref href="GUID-EC5870C2-5C3E-3DFB-9349-85AAF1A0AE58.dita"><apiname>EInput</apiname></xref> and return
value             <codeph>KErrNone.</codeph>           </p> <p>          
  Set the pin to behave as an input binary signal.           </p> </li>
<li><p>             Implement <xref href="GUID-38FAAC57-13CF-390F-AE05-8D2B9E092450.dita"><apiname>SetPinDirection()</apiname></xref> with  
          <codeph>aDirection</codeph> == <xref href="GUID-8E81439B-6FB5-3EEC-BC36-F3B70217FA8D.dita"><apiname>EOutput</apiname></xref> and return
value             <codeph>KErrNone.</codeph>           </p> <p>          
  Set the pin to behave as an output binary signal.           </p> </li>
<li><p>             Implement <xref href="GUID-38FAAC57-13CF-390F-AE05-8D2B9E092450.dita"><apiname>SetPinDirection()</apiname></xref> with  
          <codeph>aDirection</codeph> == <xref href="GUID-2AEEC0C1-CF80-3C1D-B24B-17178ACA6AB4.dita"><apiname>ETriStated</apiname></xref> and
return value             <codeph>KErrNone.</codeph>           </p> <p>   
         Set the pin to be in a quiescent state (also called floating or 
           deactivated).           </p> <p>             Only implement this
if the platform supports the quiescent             state. The physical state
of the pin will be determined by the drive on the             line.      
    </p> </li>
<li><p>             Implement <xref href="GUID-38FAAC57-13CF-390F-AE05-8D2B9E092450.dita"><apiname>SetPinDirection()</apiname></xref> with return
            value <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref>.           </p> <p> 
           Return <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref> if the pin cannot  
          operate in the direction specified, for instance if             <xref href="GUID-2AEEC0C1-CF80-3C1D-B24B-17178ACA6AB4.dita"><apiname>ETriStated</apiname></xref> has
been passed and the platform does not             support the quiescent state.
          </p> </li>
</ul></li>
<li><p>          Implement <xref href="GUID-062A11F7-123D-334C-A082-F21DB9A9EE32.dita"><apiname>GetPinDirection()</apiname></xref> for each value
         of the enumeration <xref href="GUID-2F6DB4C0-D198-39A8-B990-EF1D5B9B5901.dita"><apiname>TGpioDirection</apiname></xref>.         </p> <ul>
<li><p>             Implement <xref href="GUID-062A11F7-123D-334C-A082-F21DB9A9EE32.dita"><apiname>GetPinDirection()</apiname></xref> with  
          <codeph>aDirection</codeph> containing <xref href="GUID-EC5870C2-5C3E-3DFB-9349-85AAF1A0AE58.dita"><apiname>EInput</apiname></xref> and
return value             <xref href="GUID-6CA4F1ED-7947-3087-B618-D35858FAA3BC.dita"><apiname>KErrNone</apiname></xref>.           </p> <p> 
           Verify that the pin is behaving as a binary input signal. Set 
           <xref href="GUID-221FF753-F089-399C-BD67-A693E68AB727.dita"><apiname>aDirection</apiname></xref> to <xref href="GUID-EC5870C2-5C3E-3DFB-9349-85AAF1A0AE58.dita"><apiname>EInput</apiname></xref>    
      </p> </li>
<li><p>             Implement <xref href="GUID-062A11F7-123D-334C-A082-F21DB9A9EE32.dita"><apiname>GetPinDirection()</apiname></xref> with  
          <codeph>aDirection</codeph> containing <xref href="GUID-8E81439B-6FB5-3EEC-BC36-F3B70217FA8D.dita"><apiname>EOutput</apiname></xref> and
return             value <xref href="GUID-6CA4F1ED-7947-3087-B618-D35858FAA3BC.dita"><apiname>KErrNone</apiname></xref>.           </p> <p> 
           Verify that the pin is behaving as a binary output signal. Set
            <codeph>aDirection</codeph> to <xref href="GUID-EC5870C2-5C3E-3DFB-9349-85AAF1A0AE58.dita"><apiname>EInput</apiname></xref>     
     </p> </li>
<li><p>             Implement <xref href="GUID-062A11F7-123D-334C-A082-F21DB9A9EE32.dita"><apiname>GetPinDirection()</apiname></xref> with  
          <codeph>aDirection</codeph> containing <xref href="GUID-2AEEC0C1-CF80-3C1D-B24B-17178ACA6AB4.dita"><apiname>ETriStated</apiname></xref> and
return             value <xref href="GUID-6CA4F1ED-7947-3087-B618-D35858FAA3BC.dita"><apiname>KErrNone</apiname></xref>.           </p> <p> 
           Verify that the pin is in the quiescent state. Set             <codeph>aDirection</codeph> to <xref href="GUID-2AEEC0C1-CF80-3C1D-B24B-17178ACA6AB4.dita"><apiname>ETriStated</apiname></xref> 
         </p> </li>
<li><p>             Implement <xref href="GUID-062A11F7-123D-334C-A082-F21DB9A9EE32.dita"><apiname>GetPinDirection()</apiname></xref> with return
            value <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref>.           </p> <p> 
           Return <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref> if reading the pin 
           direction is not supported.           </p> </li>
</ul></li>
</ul> </section>
</conbody></concept>