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<title>Random</title>
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<h1><img  align="center" src="../../../icons/random.gif" width="32" height="32">
<em>Random</em></h1>

<p><table>
<tr><td><strong>Library:</strong></td>
	<td><a href="index.html">Memory</a></td></tr>
<tr><td><strong>Introduced:</strong></td>
	<td>2.3.0</td></tr>
<tr><td valign="top"><strong>Appearance:</strong></td>
	<td valign="top"><img src="../../../img-libs/random.png" width="34" height="44"></td></tr>
</table></p>

<h2>Behavior</h2>

<p>This component iterates through a pseudorandom sequence of numbers, which
steps forward to the following number in the sequence each time the clock is
triggered while the component is enabled. Technically speaking, the algorithm
used to compute the pseudorandom sequence is a linear
congruential generator: Starting from a seed
<var>r</var><sub><small>0</small></sub>, the following number
<var>r</var><sub><small>1</small></sub> is the number</p>
<center>
<var>r</var><sub><small>1</small></sub> =
(25,214,903,917 <var>r</var><sub><small>0</small></sub> + 11)
mod 2<sup><small>48</small></sup>
</center>
<p>The next value <var>r</var><sub><small>2</small></sub>
is computed from <var>r</var><sub><small>1</small></sub>
using the same computation, and so forth. This sequence is of 48-bit numbers;
the value seen from the component is the low-order bits as configured
by its Data Bits attribute, after first throwing out the lower 12 bits of
the current seed.</p>

<p>Besides the clock input, the component also includes an <var>enable</var>
input, which leads the clock input to be ignored when <var>enable</var> is 0,
and the <var>reset</var> input, which resets the component's value asynchronously
to the initial seed <var>r</var><sub><small>0</small></sub>.</p>

<p>The initial seed is user-configurable. If it is configured at 0 (which is
the default), then the seed is based on the current time; when instructed
to reset through the <var>reset</var> input, the component computes a new
seed based on the new current time.</p> 

<h2>Pins</h2>

<dl>

<dt>East edge, labeled <var>Q</var> (output, bit width matches Data Bits attribute)</dt>
<dd>Outputs the value currently stored by the component.</dd>

<dt>West edge, top pin, labeled with a triangle (input, bit width 1)</dt>
<dd>Clock: At the instant that this is triggered as specified by the Trigger
attribute, the component steps to the following number in its sequence.</dd>

<dt>West edge, bottom pin (input, bit width 1)</dt>
<dd>Enable: The component is enabled when this input is disconnected or 1;
but if it is 0, then the clock input is ignored.</dd>

<dt>South edge (input, bit width 1)</dt>
<dd>Reset: When this is 1, the pseudorandom sequence asynchronously resets to
the initial seed. (If seed is 0, this new seed should be different from the
initial seed used previously.)</dd>

</dl>


<h2>Attributes</h2>

<p>When the component is selected or being added,
Alt-0 through Alt-9 alter its <q>Data Bits</q> attribute.</p>

<dl>

<dt>Data Bits</dt>
<dd>The bit width of the value emitted by the component.</dd>

<dt>Seed</dt>
<dd>The starting value used for the pseudorandom sequence. If this is 0
(the default), then the starting value is based on the time that the random
sequence began.</dd>

<dt>Trigger</dt>
<dd>Configures how the clock input is interpreted. The value <q>rising edge</q>
indicates that the component should update its value at the instant when the
clock rises from 0 to 1. The <q>falling edge</q> value indicates that it should
update at the instant the clock falls from 1 to 0.</dd>

<dt>Label</dt>
<dd>The text within the label associated with the component.</dd>

<dt>Label Font</dt>
<dd>The font with which to render the label.</dd>

</dl>

<h2>Poke Tool Behavior</h2>

<p>None.</p>

<h2>Text Tool Behavior</h2>

<p>Allows the label associated with the component to be edited.</p>

<p><a href="../index.html">Back to <em>Library Reference</em></a></p>

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