Add Memoryboard4 documentation

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 		automatically reduced to accomodate only the remaining channels used.
 	</p>
 	<h3>Hardware</h3>
-	<p>By default, a single 23LC1024 RAM chip is used, with these pins:
+	<p>By default, or when <span class=literal>AUDIO_MEMORY_23LC1024</span> is used (see below),
+		 a single 23LC1024 RAM chip is used, with these pins:
     <table class=doc align=center cellpadding=3>
         <tr class=top><th>Pin</th><th>Signal</th></tr>
         <tr class=odd><td align=center>6</td><td>CS</td></tr>
         <tr class=odd><td align=center>12</td><td>MISO</td></tr>
         <tr class=odd><td align=center>14</td><td>SCK</td></tr>
     </table>
+	</p>
+	<p>When <span class=literal>AUDIO_MEMORY_MEMORYBOARD</span> is used, up to six
+		23LC1024 chips are used.
+	</p>
+	<p align=center><img src="memoryboard.jpg"><br><small><a href="https://oshpark.com/shared_projects/KZt5PaU7" target="_blank">Memoryboard 4</a></small></p>
+	<p>
+    <table class=doc align=center cellpadding=3>
+        <tr class=top><th>Pin</th><th>Signal</th></tr>
+        <tr class=odd><td align=center>2</td><td>CS0 (encoded)</td></tr>
+        <tr class=odd><td align=center>3</td><td>CS1 (encoded)</td></tr>
+        <tr class=odd><td align=center>4</td><td>CS2 (encoded)</td></tr>
+        <tr class=odd><td align=center>7</td><td>MOSI</td></tr>
+        <tr class=odd><td align=center>12</td><td>MISO</td></tr>
+        <tr class=odd><td align=center>14</td><td>SCK</td></tr>
+    </table>
+	</p>
+	<p>
+	If fewer than 6 chips are soldered, the optional parameter for maximum delay
+	must be used.  See below for details.  Each chip provides 1485 ms of delay
+	memory, so the total of all objects using AUDIO_MEMORY_MEMORYBOARD must not
+	exceed the amount of memory physically present.
 	</p>
 	<h3>Examples</h3>
+	<p>
 	<a href="https://www.youtube.com/watch?v=d80d1HWy5_s" target="_blank">Demo Video</a> (YouTube)
-	<!--<p class=exam>File &gt; Examples &gt; Audio &gt; Effects &gt; Delay
-	</p>-->
+	</p>
+	<!-- <p class=exam>File &gt; Examples &gt; Audio &gt; Effects &gt; Delay
+	</p> -->
+	<p>
+	<a href="https://forum.pjrc.com/threads/29276-Limits-of-delay-effect-in-audio-library?p=79436&viewfull=1#post79436" target="_blank">Forum Conversaton</a> (with sample code)
+	</p>
 	<h3>Notes</h3>
 	<p>External RAM allows for longer delays without consuming
 		limited internal RAM.  However, SPI communication is required,
 		<a href="http://www.pjrc.com/teensy/td_libs_AudioProcessorUsage.html">AudioProcessorUsageMax</a>
 		function may be used to monitor how much CPU time is consumed.
 	</p>
-	<p>You may specify the type of hardware to be used by editing the code.  Currently, AUDIO_MEMORY_23LC1024
-		is the only supported option.  Future support for AUDIO_MEMORY_MEMORYBOARD is
-		planned.
+	<p>You may specify the type of hardware to be used by editing the code.  AUDIO_MEMORY_23LC1024
+		specifies a single 23LC1024 chip.  AUDIO_MEMORY_MEMORYBOARD allows using up to 6 of these
+		chips.
 	</p>
 	<p class=desc><span class=keyword>AudioEffectDelayExternal</span>  delayExt1(<span class=literal>AUDIO_MEMORY_23LC1024</span>);
 	</p>