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<!DOCTYPE html>
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<title>LogixNG Reference - Chapter 6</title>
<meta name="author" content="Daniel Bergqvist">
<meta name="author" content="Dave Sand">
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<h1>LogixNG Reference - Chapter 6</h1>
<h2>Expression Descriptions</h2>
<p>The expression descriptions are grouped by the socket type and category.</p>
<p class="noted"><span class="since">since 5.1.3</span>The <strong>Call Module</strong>
expression has been moved from the <strong><em>Other</em></strong> category to the <strong><em>
Flow Control</em></strong> category.</p>
<ul>
<li>Digital expression
<ul>
<li>
<a href="#digital_expression_item">Item</a>
</li>
<li>
<a href="#digital_expression_common">Common</a>
</li>
<li>
<a href="#digital_expression_flow_control">Flow Control <span class="since">since 5.1.3</span></a>
</li>
<li>
<a href="#digital_expression_loconet">LocoNet</a>
</li>
<li>
<a href="#digital_expression_linux">Linux <span class="since">since 5.3.4</span></a>
</li>
<li>
<a href="#digital_expression_other">Other</a>
</li>
</ul>
</li>
<li>Analog expression
<ul>
<li>
<a href="#analog_expression_item">Item</a>
</li>
<li>
<a href="#analog_expression_common">Common</a>
</li>
</ul>
</li>
<li>String expression
<ul>
<li>
<a href="#string_expression_item">Item</a>
</li>
<li>
<a href="#string_expression_common">Common</a>
</li>
</ul>
</li>
<li>
<a href="#generic_expression">Generic Expression</a>
</li>
</ul>
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<h3>Expression dialogs</h3>
<p>When the category and type has been selected, the detail expression dialog will be
displayed. The content of the dialog will vary depending on the category and type. The
typical digital expression item dialog is described below.</p>
<p>The dialog for adding and editing expressions consists of an upper part that contains the
item and the states for that item. The lower part is common to all expressions.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/typical_expression.png"><img src=
"images/chapter6/typical_expression.png" alt="Chapter 6 typical expression"></a>
</div>
<p>The <strong>Edit</strong> screen is the same except for the title, the Create button and
the current content will be in the fields.</p>
<p>The left section is normally used to select the item, such as a turnout or a sensor. The
right section is the state to be checked. The center section will normally have a <strong>is
/ is not</strong> combo box. The default mode will be to use the <strong>Direct</strong>
tabs.</p>
<p>See <a href="chapter7.shtml">Reference</a>, <a href="chapter8.shtml">Local Variable</a>
and <a href="chapter9.shtml">Formula</a> for details about the other tabs.</p>
<p>The lower section contains a standard set of items</p>
<dl>
<dt>Error Handling</dt>
<dd>
If <strong>Use default</strong> is selected, the value in <a href=
"../LogixNG.shtml#preferences">Preference</a> will be used. For other options see
<a href="../ErrorHandling.shtml">error handling</a>.
</dd>
<dt>Catch "Abort execution"</dt>
<dd>If the error handling (see previous) for any child node is set to <strong>Abort
execution</strong>, a parent node should have this option checked. This lets the parent
node handle the error.</dd>
<dt>Listen</dt>
<dd>Normally, any change to an expression item should trigger the true/false evaluation.
Sometimes an expression item should participate in the evaluation but not trigger it. The
Listen checkbox is used to control the trigger state.</dd>
<dt>Edit comment</dt>
<dd>Each expression can have a comment. The comment dialog has a multiline text area. Click
<strong>OK</strong> to save the comment.</dd>
<dt>Formula functions</dt>
<dd>
These are explained in the <a href="chapter9.shtml">Formula</a> chapter.
</dd>
<dt>Cancel</dt>
<dd>Close the dialog without applying any changes.</dd>
<dt>Create/OK</dt>
<dd>Save the new expression or the changes to an existing expression.</dd>
</dl>
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<h3 id="digital_expression_item">Digital expression :: Item</h3>
<ul class="sub-links">
<li><a href="#item_audio">Audio</a></li>
<li><a href="#item_block">Block</a></li>
<li><a href="#item_clock">Clock</a></li>
<li><a href="#item_conditional">Conditional</a></li>
<li><a href="#item_dispatcher">Dispatcher</a></li>
<li><a href="#EntryExitExpressions">Entry/Exit</a></li>
<li><a href="#item_light">Light</a></li>
<li><a href="#item_local_variable">Local variable</a></li>
<li><a href="#item_memory">Memory</a></li>
<li><a href="#item_oblock">OBlock</a></li>
<li><a href="#item_power">Power</a></li>
<li><a href="#item_reference">Reference</a></li>
<li><a href="#item_reporter">Reporter</a></li>
<li><a href="#script">Script</a></li>
<li><a href="#item_section">Section</a></li>
<li><a href="#item_sensor">Sensor</a></li>
<li><a href="#item_sensor_edge">Sensor Edge</a></li>
<li><a href="#item_signal_head">Signal head</a></li>
<li><a href="#item_signal_mast">Signal mast</a></li>
<li><a href="#item_transit">Transit</a></li>
<li><a href="#item_turnout">Turnout</a></li>
<li><a href="#WarrantExpression">Warrant</a></li>
</ul>
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<h5 id="item_audio">Audio<span class="since">since 5.5.4</span></h5>
<p>Returns true if the selected audio object has the indicated state. The drop-down list
contains the defined audio listeners and audio sources.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/digital_expression_audio.png"><img src=
"images/chapter6/digital_expression_audio.png" alt="Chapter 6 expression audio item"></a>
</div>
<p>The <strong>Check only on change</strong> option is used to change the logic of the
expression evaluation. When the option is not enabled, the normal evaluation occurs:
<strong><em>Does the current state match the indicated state</em></strong>. When the option
is enabled, the evaluation becomes: <strong><em>Has the current state changed to the indicated
state since the last check</em></strong>.
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_block">Block</h5>
<ul>
<li><strong>Occupied:</strong> Evaluate to true if the sensor assigned to the block is
active.</li>
<li><strong>not Occupied:</strong> Evaluate to true if the sensor assigned to the block is
inactive.</li>
<li><strong>some other state:</strong> Evaluate to true if the state is unknown,
inconsistent or undetected.</li>
<li><strong>Allocated:</strong> Evaluate to true if the related layout block has use extra
color enabled.</li>
<li><strong>equal to:</strong> Evaluate to true if the value of the block matches a string
value or a reference value, which is typically a memory variable.</li>
</ul>
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<h5 id="item_clock">Clock</h5>
<ul>
<li><strong>Fast clock:</strong> Evaluate to true if the fast clock time is between two
hh:mm values.</li>
<li><strong>System clock:</strong> Evaluate to true if the system clock time is between two
hh:mm values.</li>
</ul>
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<h5 id="item_conditional">Conditional</h5>
<p>If the conditional named is used in more than one Logix, the results are
unpredictable.</p>
<ul>
<li><strong>False:</strong> Evaluate to true if the state of the specified conditional is
false.</li>
<li><strong>True:</strong> Evaluate to true if the state of the specified conditional is
true.</li>
<li><strong>Other:</strong> Evaluate to true if the state of the specified conditional is
unknown or inconsistent.</li>
</ul>
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<h5 id="item_dispatcher">Dispatcher</h5>
<p>A Dispatcher train only exists from the time it is created until it is terminated.
LogixNG uses the Dispatcher TrainInfo file to refer to a potential Dispatcher train.
See the <em>Saving and Retrieving Active Train Information</em> section at
<a href="https://www.jmri.org/help/en/package/jmri/jmrit/dispatcher/NewTrain.shtml">
Activate New Train</a>. The train is started using the LogixNG Dispatcher
<em>Load train from train info file</em> Action. If the related train does not exist when
the expression is evaluated, the result will be false. That means a false result is either
actually false or the train does not exist.</p>
<p>Train Mode:</p>
<ul>
<li><strong>Automatic</strong></li>
<li><strong>Dispatched</strong></li>
<li><strong>Manual</strong></li>
</ul>
<p>Train Status:</p>
<ul>
<li><strong>Running</strong></li>
<li><strong>Paused</strong></li>
<li><strong>Waiting</strong></li>
<li><strong>Working</strong></li>
<li><strong>Ready</strong></li>
<li><strong>Stopped</strong></li>
<li><strong>Done</strong></li>
</ul>
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<h5 id="EntryExitExpressions">Entry/Exit</h5>
<p>Evaluate if an Entry/Exit pair has a specified state.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/entryexit_expression.png"><img src=
"images/chapter6/entryexit_expression.png" alt="Chapter 6 entryexit expression"></a>
</div>
<dl>
<dt>Inactive</dt>
<dd>Evaluate to true if the state of the specified entry/exit pair is inactive.</dd>
<dt>Active</dt>
<dd>Evaluate to true if the state of the specified entry/exit pair is active.</dd>
<dt>Other</dt>
<dd>Evaluate to true if the state of the specified entry/exit pair is unknown or inconsistent.</dd>
<dt>Reversed</dt>
<dd>Evaluate to true if the specified entry/exit pair is <strong>active</strong> and
<strong>reversed</strong>. A <strong>reversed</strong> route occurs when the sensors for a
<strong>bidirectional</strong> entry/exit pair are selected in the reverse order. The
evaluation is triggered by a change to the active/inactive state of the entry/exit pair.</dd>
<dt>Bidirectional</dt>
<dd>Evaluate to true if the specified entry/exit pair has the <strong>Both Way</strong>
option enabled in the entry/exit pair table. The evaluation is triggered by a change to
the active/inactive state of the entry/exit pair. Changes to the Both Way option do not
trigger evaluation.</dd>
</dl>
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<h5 id="item_light">Light</h5>
<ul>
<li><strong>Off:</strong> Evaluate to true if the state of the specified light is off.</li>
<li><strong>On:</strong> Evaluate to true if the state of the specified light is on.</li>
<li><strong>Other:</strong> Evaluate to true if the state of the specified light is unknown
or inconsistent.</li>
</ul>
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<h5 id="item_local_variable">Local variable</h5>
<p>Compares the value of the specified local variable to either a string, a memory variable,
another local variable or a table cell. See <a href="chapter11.shtml#tableCellSelection">
Simplified Table Cell Reference</a> for details on defining the table cell. Evaluates to true
if the comparison is true.</p>
<ul>
<li><strong>is less than</strong>
</li>
<li><strong>is less than or equal</strong>
</li>
<li><strong>is equal to</strong>
</li>
<li><strong>is greater than or equal to</strong>
</li>
<li><strong>is greater than</strong>
</li>
<li><strong>is not equal to</strong>
</li>
<li><strong>is null</strong>
</li>
<li><strong>is not null</strong>
</li>
<li><strong>does match regular expression</strong>
</li>
<li><strong>does not match regular expresson</strong>
</li>
</ul>
<p>The <strong><em>Type</em></strong> indicates the how the comparison process works.</p>
<ul>
<li><strong>Number or string</strong> &mdash; The comparison is based on the characteristics
of the objects.</li>
<li><strong>String</strong> &mdash; The comparison is based on the string values of the
objects.</li>
<li><strong>Number</strong> &mdash; The comparison is based on the numeric values of the
objects. This can result in an exception if any of the values is not a number.</li>
</ul>
<p>For information about regular expressions, see:
https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html</p>
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<h5 id="item_memory">Memory</h5>
<p>Compares the value of the specified memory variable to either a string, another memory,
variable, a local variable or a table cell. See <a href="chapter11.shtml#tableCellSelection">
Simplified Table Cell Reference</a> for details on defining the table cell. Evaluates to true
if the comparison is true.</p>
<ul>
<li><strong>is less than</strong>
</li>
<li><strong>is less than or equal</strong>
</li>
<li><strong>is equal to</strong>
</li>
<li><strong>is greater than or equal to</strong>
</li>
<li><strong>is greater than</strong>
</li>
<li><strong>is not equal to</strong>
</li>
<li><strong>is null</strong>
</li>
<li><strong>is not null</strong>
</li>
<li><strong>does match regular expression</strong>
</li>
<li><strong>does not match regular expresson</strong>
</li>
</ul>
<p>The <strong><em>Type</em></strong> indicates the how the comparison process works.</p>
<ul>
<li><strong>Number or string</strong> &mdash; The comparison is based on the characteristics
of the objects.</li>
<li><strong>String</strong> &mdash; The comparison is based on the string values of the
objects.</li>
<li><strong>Number</strong> &mdash; The comparison is based on the numeric values of the
objects. This can result in an exception if any of the values is not a number.</li>
</ul>
<p>For information about regular expressions, see:
https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_oblock">OBlock</h5>
<ul>
<li><strong>Unoccupied:</strong> Evaluate to true if the specified oblock is not
occupied.</li>
<li><strong>Occupied:</strong> Evaluate to true if the specified oblock is occupied.</li>
<li><strong>Allocated:</strong> Evaluate to true if the specified oblock is allocated.</li>
<li><strong>Running:</strong> Evaluate to true if the specified oblock is running (is path
occupied in Logix).</li>
<li><strong>OutOfService:</strong> Evaluate to true if the specified oblock is out of
service.</li>
<li><strong>Dark:</strong> Evaluate to true if the specified oblock is dark.</li>
<li><strong>TrackError:</strong> Evaluate to true if the specified oblock has a track error
(is power error in Logix).</li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_power">Power</h5>
<ul>
<li><strong>On:</strong> Evaluate to true if the power state is on.</li>
<li><strong>Off:</strong> Evaluate to true if the power state is off.</li>
<li><strong>Idle:</strong> Evaluate to true if the power state is idle.<span class="since">
since 5.1.6</span></li>
<li><strong>Unknown:</strong> Evaluate to true if the power state is unknown.</li>
<li><strong>On or Off:</strong> Evaluate to true if the power state is on or
off. Previously this was the <strong>Other</strong> state.<span class="since">since 5.1.6</span></li>
</ul>
<p>The <strong>Ignore unknown state</strong> option is used to bypass the the unknown state.
This can occur when transitioning between the <strong>on</strong> and <strong>off</strong>
states.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_reference">Reference</h5>
<p>If there is a possibility that a <a href="chapter7.shtml">reference</a> will refer to an
item that does not exist or it is the wrong item type, the Reference expression can test that
case and return true or false.</p>
<p>An example would be a <a href="chapter11.shtml">table</a> that has optional cells. A table
for a staging yard ladder will have a variable number of turnouts based on the selected
track.</p>
<p>Enter the reference to be checked and specify the type.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/reference_dialog.png"><img src=
"images/chapter6/reference_dialog.png" alt="Chapter 6 reference dialog"></a>
</div>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_reporter">Reporter</h5>
<p>Compare the content of one of the three Reporter data fields to a string, a memory variable
or a local variable. See the <strong>Memory</strong> description for a list of the
comparisons.</p>
<ul>
<li><strong>Current Report:</strong> The current value unless the hardware says there is
nothing to report. In that case the value will be null.</li>
<li><strong>Last Report:</strong> Normally the current report and last report are the same.
If the current report is null, this will be most recent valid report. If no report has ever
been received, this will be null.</li>
<li><strong>State:</strong> A number that represents the last report.</li>
</ul>
<p>Note: The meaning of the reports and the state number are defined by originating
hardware.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="script">Script</h5>
<p>A script expression calls a Jython or ECMAScript script. The script context contains a
<strong>result</strong> boolean object. When the script is done, it does a
<code>result.setValue(x)</code> where x is, or evaluates to, True or False.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/digital_expression_script.png">
<img src="images/chapter6/digital_expression_script.png" alt="Chapter 6 digital expression script"></a>
</div>
<p>The Register listener and Unregister listener options are used if the script is to run
based on some other JMRI event. For example, the following register command will
cause the script to be run every fast minute.</p>
<code>memories.getMemory('IMCURRENTTIME').addPropertyChangeListener('value', self)</code>
<p>Select the type of script. The supported script types are <strong>Jython Files</strong>
and <strong>ECMAScript Files</strong>.</p>
<p>For details on accessing LogixNG objects from a script see <a href="chapter13.shtml">
Chapter 13 - Jython Scripting Support</a>.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_section">Section<span class="since">since 5.3.5</span></h5>
<ul>
<li><strong>Free:</strong> Evaluate to true if the state of the selected section is
not being used by a transit.</li>
<li><strong>Forward:</strong> Evaluate to true if the selected section is being used by
a transit and is set for the forward direction.</li>
<li><strong>Reverse:</strong> Evaluate to true if the selected section is being used by
a transit and is set for the reverse direction.</li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_sensor">Sensor</h5>
<ul>
<li><strong>Inactive:</strong> Evaluate to true if the state of the specified sensor is
inactive.</li>
<li><strong>Active:</strong> Evaluate to true if the state of the specified sensor is
active.</li>
<li><strong>Other:</strong> Evaluate to true if the state of the specified sensor is
unknown or inconsistent.</li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_sensor_edge">Sensor Edge<span class="since">since 5.1.7</span></h5>
<p>Returns True if the state of the sensor goes from one predefined state to another, for
example from "Active" to "Inactive".</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/expression_sensor_edge.png">
<img src="images/chapter6/expression_sensor_edge.png" alt="Chapter 6 expression sensor edge"></a>
</div>
<p>If the option <strong>Only true on the first occurrence</strong> is selected, the
expression will only return True once and there after return False. This is useful if you want
the expression to return True only the first time it is evaluated.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_signal_head">Signal head</h5>
<ul>
<li><strong>has appearance:</strong> Evaluate to true if the specified signal head
appearance matches the selected appearance.</li>
<li><strong>has not appearance:</strong> Evaluate to true if the specified signal head
appearance does not match the selected appearance.</li>
<li><strong>is lit:</strong> Evaluate to true if the state of the specified signal head is
lit.</li>
<li><strong>is not lit:</strong> Evaluate to true if the state of the specified signal head
is no lit.</li>
<li><strong>is held:</strong> Evaluate to true if the state of the specified signal head is
held.</li>
<li><strong>is not held:</strong> Evaluate to true if the state of the specified signal
head is not held.</li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_signal_mast">Signal mast</h5>
<ul>
<li><strong>has aspect:</strong> Evaluate to true if the specified signal mast aspect
matches the selected aspect.</li>
<li><strong>has not aspect:</strong> Evaluate to true if the specified signal mast aspect
does not match the selected aspect.</li>
<li><strong>is lit:</strong> Evaluate to true if the state of the specified signal mast is
lit.</li>
<li><strong>is not lit:</strong> Evaluate to true if the state of the specified signal mast
is no lit.</li>
<li><strong>is held:</strong> Evaluate to true if the state of the specified signal mast is
held.</li>
<li><strong>is not held:</strong> Evaluate to true if the state of the specified signal
mast is not held.</li>
<li><strong>is permissive sml disabled:</strong> Evaluate to true if the specified signal
mast has permissive sml disabled.</li>
<li><strong>is not permissive sml disabled:</strong> Evaluate to true if the specified
signal does not have permissive sml disabled.</li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_transit">Transit<span class="since">since 5.3.5</span></h5>
<ul>
<li><strong>Idle:</strong> Evaluate to true if the state of the selected transit is
idle. This indicates that the transit is not been assigned to an active train.</li>
<li><strong>Assigned:</strong> Evaluate to true if the selected transit is assigned to an
active train by the Dispatcher tool.</li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="item_turnout">Turnout</h5>
<ul>
<li><strong>Closed:</strong> Evaluate to true if the state of the specified turnout is
closed.</li>
<li><strong>Thrown:</strong> Evaluate to true if the state of the specified turnout is
thrown.</li>
<li><strong>Other:</strong> Evaluate to true if the state of the specified turnout is
unknown or inconsistent.</li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="WarrantExpression">Warrant</h5>
<ul>
<li><strong>Route free:</strong> Evaluate to true if the specified route is available.</li>
<li><strong>Route occupied:</strong> Evaluate to true if the specified route is
occupied.</li>
<li><strong>Route allocated:</strong> Evaluate to true if the specified route has been
allocated.</li>
<li><strong>Route set:</strong> Evaluate to true if the specified turnout has been
set.</li>
<li><strong>Train is running:</strong> Evaluate to true if the specified route has a train
running.</li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="digital_expression_common">Digital expression :: Common</h3>
<ul class="sub-links">
<li><a href="#common_and">And</a></li>
<li><a href="#common_antecedent">Antecedent</a></li>
<li><a href="#digital_formula">Digital Formula</a></li>
<li><a href="#common_not">Not</a></li>
<li><a href="#common_or">Or</a></li>
<li><a href="#timer_id">Timer</a></li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="common_and">And</h5>
<p>And evaluates the child expressions and if all of them returns true, the And expression
returns true as well.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="common_antecedent">Antecedent</h5>
<p>The Antecedent expression is mainly included to make import from Logix to LogixNG simple.
It works exactly as Antecedent in Logix. It has a number of child expressions and an
antecedent that defines how the evaluation of the expressions should be done. Each child
expression is referenced in the antecedent by R1, R2, R3, ..., there R1 is the first child
expression, R2 is the second child expression, and so on. Note that this differs from other
expressions in LogixNG. Other LogixNG expressions use the socket name, but since the
Antecedent expression is included to work as Antecedent works in Logix, the antecedent has
been kept from Logix Antecedent as well. <em>Note: Antecedent is included for compatibility
with Logix but it's recommended to use Formula instead. Formula is much more powerful, uses
the socket names and also works with numbers and strings.</em></p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="digital_formula">Digital Formula</h5>
<p>Formula is the next generation of Antecedent. It supports many operators, like ==, !=,
&lt;=, &gt;=, &lt;, &gt;, +, -, *, / and %. It supports local variables, memories and
functions. It supports all the types of expressions, digital, analog and string expressions.
See <a href="#generic_expression">Generic expression</a> for details on the result of merging
the other expressions.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="common_not">Not</h5>
<p>The Not expression has one child expression and answers <strong>true</strong> if the child
expression answers <strong>false</strong>, and <strong>false</strong> if the child expression
answers <strong>true</strong>.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="common_or">Or</h5>
<p>Or evaluates the child expressions and if at least one of them returns true, the Or
expression returns true as well.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="timer_id">Timer</h5>
<p>The <strong>Timer</strong> expression returns <strong>False</strong> until some time has
passed. It then returns <strong>True</strong> once and the timer starts again. This expression
is intended to be used together with the <a href="chapter5#sequence_id">Sequence</a> action.
This makes it possible to have sequence steps based on time durations.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/timer_expression.png"><img class="image-border" src=
"images/chapter6/timer_expression.png"
alt="Chapter 6 timer expression"></a>
</div>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="digital_expression_flow_control">Digital expression :: Flow Control
<span class="since">since 5.1.3</span></h3>
<ul class="sub-links">
<li><a href="#flow_call_module">Call module</a></li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="flow_call_module">Call module</h5>
<p>Call a module and and return its true/false response. See <a href=
"chapter10.shtml#DigitalExpressionModule">Chapter 10 - Modules</a></p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="digital_expression_loconet">Digital expression :: LocoNet</h3>
<ul class="sub-links">
<li><a href="#loconet_slot_usage">Slot Usage</a></li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="loconet_slot_usage">Slot Usage</h5>
<p>Evaluate the LocoNet slot usage.</p>
<div style="margin-left: 2em">
<a href="images/chapter6/loconet_slot_usage.png"><img src=
"images/chapter6/loconet_slot_usage.png" alt="Chapter 6 loconet slot usage"></a>
</div>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="digital_expression_linux">Digital expression :: Linux</h3>
<ul class="sub-links">
<li><a href="#linux_line_power">Linux Line Power</a></li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="linux_line_power">Linux Line Power<span class="since">since 5.3.4</span></h5>
<p>The Linux <strong>upower</strong> command line tool is used to determine if external power
is active. For example, if the external power is removed, then this tool can be used to do a
graceful shutdown before the battery dies.</p>
<p>The expression runs the <strong>upower</strong> command line tool every five seconds. If
it detects a change, it triggers the execution of the ConditionalNG.</p>
<p>When the expression is added, the <strong>upower</strong> command is checked to make sure
it is present and working. A warning message will be displayed if there is an issue.</p>
<div style="margin-left: 2em">
<a href="images/chapter6/linux_line_power.png"><img src=
"images/chapter6/linux_line_power.png" alt="Chapter 6 linux line power"></a>
</div>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="digital_expression_other">Digital expression :: Other</h3>
<ul class="sub-links">
<li><a href="#other_always_false">Always false</a></li>
<li><a href="#other_always_true">Always true</a></li>
<li><a href="#connectname">Connection name</a></li>
<li><a href="#fileasflag">File as flag</a></li>
<li><a href="#other_hold">Hold</a></li>
<li><a href="#LastResult">Last result of digital expression</a></li>
<li><a href="#other_log_data">Log data</a></li>
<li><a href="#other_trigger_once">Trigger once</a></li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="other_always_false">Always false</h5>
<p>The False expression always answers <strong>false</strong>.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="other_always_true">Always true</h5>
<p>The True expression always answers <strong>true</strong>. This expression is commonly used
as a child to the Trigger Once expression.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="connectname">Connection name<span class="since">since 5.1.3</span></h5>
<p>The <strong>Connection name</strong> expression returns <strong>true</strong> if the
selected manufacturer and connection type match a connection in <strong>Preferences &rArr;
Connections</strong>.</p>
<p>This can be used to determine whether JMRI is using a real layout connection or a simulated
connection. For example, a startup LogixNG can set an internal sensor that indicates the
simulation state. Other LogixNG definitions can then check the state to determine what actions
are appropriate. A good example is whether the <a href="chapter5.shtml#simfeedback">Simulate
turnout feedback</a> action should be used.</p>
<p>The connection name is selected by choosing the manufacturer and then a connection name
from the connection list.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/connection_expression.png"><img src=
"images/chapter6/connection_expression.png" alt="Chapter 6 connection expression"></a>
</div>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="fileasflag">File as flag<span class="since">since 5.5.2</span></h5>
<p>The <strong>File as flag</strong> expression checks for the existence of a file. If the
file exists, the expression returns <strong>true</strong>, otherwise it returns <strong>false
</strong>. When the file is found, it can be kept or deleted. Normally the file will be
created by some process that needs to notify JMRI about an event. For Linux and macOS,
<strong><code>touch <em>filename</em></code></strong> works from the command line or a script.
The are several options for Windows, such as
<strong><code>copy nul <em>filename</em></code></strong>,
<strong><code>type nul > <em>filename</em></code></strong>, or
<strong><code>echo > <em>filename</em></code></strong>.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/file_as_flag.png"><img src=
"images/chapter6/file_as_flag.png" alt="Chapter 6 file as flag expression"></a>
</div>
<p>The file selector is used to create the path to the file and file name. The
default path is the <strong>user files location</strong>. If the file does not
currently exist, select a different file and then replace the file name with the
planned file name before creating the expression.</p>
<p>The default file action when the file is found is <strong>Keep file</strong>. The
<strong>Delete file</strong> action can be selected which would be useful for
repetitive external events.</p>
<p><strong><u>Example</u></strong></p>
<p>The LogixNG <a href="chapter5.shtml#timeraction">Timer</a> action is used to
run the <strong>File as flag</strong> expresson every 5 seconds. When the file
exists, an internal sensor is set <strong>Active</strong>. The file is deleted and
the timer loop resumes running <strong>File as flag</strong>. The sensor is used
to trigger another process which handles the event. For simple actions,
<strong>Then</strong> could be used to do the work.</p>
<p>Configure the Timer action.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/file_as_flag_ex_timer.png"><img src=
"images/chapter6/file_as_flag_ex_timer.png" alt="Chapter 6 file as flag timer"></a>
</div>
<p>Create the LogixNG.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/file_as_flag_ex_lng.png"><img src=
"images/chapter6/file_as_flag_ex_lng.png" alt="Chapter 6 file as flag example"></a>
</div>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="other_hold">Hold</h5>
<p>The Hold expression has two child expressions, one trigger expression and one hold
expression. For this expression to become <strong>true</strong>, both the trigger expression
and the hold expression must answer <strong>true</strong>. But then it stays
<strong>true</strong> as long as the hold expression stays <strong>true</strong>.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="LastResult">Last result of digital expression</h5>
<p>Each digital expression retains its most recent true/false state. This can be checked if
the expression has a user name. See <a href="chapter3.shtml">Chapter 3</a>. Select the user
name from the combo box.</p>
<div style="margin-left: 2em">
<a href="images/chapter6/expression_last_result.png"><img src=
"images/chapter6/expression_last_result.png" alt="Chapter 6 expression last result"></a>
</div>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="other_log_data">Log data</h5>
<p>The <strong>Log data</strong> expresson works the same as the <strong>Log data</strong>
action. See <a href="chapter5.shtml#ActionLogData">Log data action</a> for details.</p>
<p>Since this is an expression, it must return true or false. The window for creating the
expression version includes a combo box for selecting True or False</p>
<div style="margin-left: 2em">
<a href="images/chapter6/log_data_return.png"><img src=
"images/chapter6/log_data_return.png" alt="Chapter 6 log data return options"></a>
</div>
<p><strong>True</strong> is recommended for <strong>And</strong> expressions and
<strong>False</strong> for <strong>Or</strong> expressions.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="other_trigger_once">Trigger once</h5>
<p>The TriggerOnce expression answers true one single time and then false until its child
expression becomes False and then True again.</p>
<p>Most often, the TriggerOnce expression will have the expression Always true as its child
and it will then answers true one single time and then false until JMRI is restarted.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="analog_expression_item">Analog expression :: Item</h3>
<ul class="sub-links">
<li><a href="#analog_constant">Analog constant</a></li>
<li><a href="#analog_io">AnalogIO</a></li>
<li><a href="#analog_local_variable">Local variable as analog value</a></li>
<li><a href="#analog_memory">Memory as analog value</a></li>
<li><a href="#MidnightMinutes">Minutes since midnight</a></li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="analog_constant">Analog constant</h5>
<p>Return a constant as an analog value.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="analog_io">AnalogIO</h5>
<p>AnalogIO reads the value of an AnalogIO and returns its value. There is currently two
items that can be used with AnalogIO:</p>
<ul>
<li>Variable lights</li>
<li>Meters</li>
</ul>
<p>Some connections supports meters, for example current and/or voltage meters. This depends
on the hardware connected to JMRI. An example is the Roco Z21 that has a current and voltage
meter that JMRI can listen to.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="analog_local_variable">Local variable as analog value</h5>
<p>Return value of a local variable as an analog value.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="analog_memory">Memory as analog value</h5>
<p>Return value of a memory variable as an analog value.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="MidnightMinutes">Minutes since midnight</h5>
<p>Return the number of minutes since midnight using either the fast clock or the system
clock.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="analog_expression_common">Analog expression :: Common</h3>
<ul class="sub-links">
<li><a href="#analog_formula">Analog formula</a></li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="analog_formula">Analog formula</h5>
<p>Return the result of a formula as an analog value.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="string_expression_item">String expression :: Item</h3>
<ul class="sub-links">
<li><a href="#mem_expression">Memory as string value</a></li>
<li><a href="#con_expression">String constant</a></li>
<li><a href="#sio_expression">StringIO as string value</a></li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="mem_expression">Memory as string value</h5>
<p>Return the value of a memory variable as a string value.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="con_expression">String constant</h5>
<p>Return a constant as a string value.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="sio_expression">StringIO as string value</h5>
<p><span class="since">since 5.11.2</span>Return the value of a StringIO as a string value.
StringIOs are defined in the <a href="../../StringIO.shtml">StringIO</a> table.</p>
<p>This can be used to provide an argument for an If statement. The following example tests a
StringIO value for a match.</p>
<div style="margin-left: 2em;">
<a href="images/chapter6/if_stringio_value.png"><img class="image-border" src=
"images/chapter6/if_stringio_value.png" alt="Chapter 6 if stringio value"></a>
</div>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="string_expression_common">String expression :: Common</h3>
<ul class="sub-links">
<li><a href="#common_string_formula">String formula</a></li>
</ul>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h5 id="common_string_formula">String formula</h5>
<p>Return the result of a formula as a string value.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="generic_expression">Generic expression</h3>
<p>The <a href="#digital_formula">Digital Formula</a> expression can use any of the other
expressions. This means the lists from the other sockets and categories are combined.</p>
<p>The combined <strong>Item</strong> list:</p>
<ul class="sub-links">
<li><a href="#analog_constant">Analog constant</a></li>
<li><a href="#analog_io">AnalogIO</a></li>
<li><a href="#item_audio">Audio</a></li>
<li><a href="#item_block">Block</a></li>
<li><a href="#item_clock">Clock</a></li>
<li><a href="#item_conditional">Conditional</a></li>
<li><a href="#item_dispatcher">Dispatcher</a></li>
<li><a href="#EntryExitExpressions">Entry/Exit</a></li>
<li><a href="#item_light">Light</a></li>
<li><a href="#item_local_variable">Local variable</a></li>
<li><a href="#analog_local_variable">Local variable as analog value</a></li>
<li><a href="#item_memory">Memory</a></li>
<li><a href="#analog_memory">Memory as analog value</a></li>
<li><a href="#mem_expression">Memory as string value</a></li>
<li><a href="#MidnightMinutes">Minutes since midnight</a></li>
<li><a href="#item_oblock">OBlock</a></li>
<li><a href="#item_power">Power</a></li>
<li><a href="#item_reference">Reference</a></li>
<li><a href="#item_reporter">Reporter</a></li>
<li><a href="#script">Script</a></li>
<li><a href="#item_section">Section</a></li>
<li><a href="#item_sensor">Sensor</a></li>
<li><a href="#item_sensor_edge">Sensor Edge</a></li>
<li><a href="#item_signal_head">Signal head</a></li>
<li><a href="#item_signal_mast">Signal mast</a></li>
<li><a href="#con_expression">String constant</a></li>
<li><a href="#sio_expression">StringIO as string value</a></li>
<li><a href="#item_transit">Transit</a></li>
<li><a href="#item_turnout">Turnout</a></li>
<li><a href="#WarrantExpression">Warrant</a></li>
</ul>
<p>The combined <strong>Common</strong> list:</p>
<ul class="sub-links">
<li><a href="#analog_formula">Analog formula</a></li>
<li><a href="#common_and">And</a></li>
<li><a href="#common_antecedent">Antecedent</a></li>
<li><a href="#digital_formula">Digital Formula</a></li>
<li><a href="#common_not">Not</a></li>
<li><a href="#common_or">Or</a></li>
<li><a href="#common_string_formula">String formula</a></li>
<li><a href="#timer_id">Timer</a></li>
</ul>
<p>The <strong>Flow Control</strong>, <strong>LocoNet</strong> and <strong>Other</strong> lists
are the same as Digital expression.</p>
<hr>
<p><a href="chapter7.shtml">Chapter 7 - References</a>
</p>
<p><a href="index.shtml">Return to the Reference TOC</a>
</p>
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