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<title>Tunnel</title>
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<h1><img  align="center" src="../../../../en/icons/tunnel.gif" width="32" height="32">
<em>Tunnel</em></h1>

<p><table>
<tr><td><strong>Library:</strong></td>
	<td><a href="index.html">Wiring</a></td></tr>
<tr><td><strong>Introduced:</strong></td>
	<td>2.5.0 (in Base library, moved to Wiring in 2.7.0)</td></tr>
<tr><td valign="top"><strong>Appearance:</strong></td>
	<td valign="top"><img src="../../../../en/img-libs/tunnel.png" width="220" height="90"></td></tr>
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<h2>Behavior</h2>

<p>A <q>tunnel</q> acts like a wire in that it binds points together,
but unlike a wire the connection is not explicitly drawn.
This is helpful when you need to connect points far apart in the circuit
and a network of wires would make the circuit much more ugly.
The below illustration illustrates how this works.</p>

<blockquote><img src="../../../../en/img-libs/tunnel-demo.png" width="204" height="86"></blockquote>

<p>Here, all three tunnels have the same label, <em>a</em>, and so
the three points to which the tunnels point are connected.
(If one of the tunnels were labeled something else, like <em>b</em>,
then it would be part of a different set of tunnels.)
The controlled buffer at top emits a floating output
since its lower input is 0.
This normally leads the wire coming from the controlled buffer to be blue;
but here it is dark green because the floating output combines
through the tunnel with the 0 from the pin at bottom.
If the control input into the buffer changes to 1,
then the controlled buffer would feed 1 into the tunnel,
which would combine with 0 from the pin at bottom to result in an error value; thus, we would then see red wires feeding through all three tunnels.</p>

<h2>Pins</h2>

<p>A tunnel has only one pin, whose bit width matches the tunnel's
Data Bits attribute. This pin is neither an input nor an output &mdash;
the matching tunnels are simply connected transparently.</p>

<h2>Attributes</h2>

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

<dl>

<dt>Facing</dt>
<dd>The direction toward which the tunnel points.</dd>

<dt>Data Bits</dt>
<dd>The number of bits for the tunnel.</dd>

<dt>Label</dt>
<dd>The text within the label associated with the tunnel.
This tunnel is connected to all other tunnels with exactly the same label.</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 tunnel to be edited.</p>

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

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