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183 lines
7.7 KiB
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183 lines
7.7 KiB
Plaintext
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<meta name="generator" content="HTML Tidy for HTML5 for Apple macOS version 5.8.0">
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<title>JMRI Hardware Support - Modbus</title><!--#include virtual="/help/en/parts/Style.shtml" -->
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<body>
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<div id="mainContent">
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<img src="https://modbus.org/images/logo_new.jpg" alt="Modbus logo" height="40" width=
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"145" class="floatRight">
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<h1>Hardware Support: Modbus</h1>
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<b>There is no released JMRI support for anything on this page yet.
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This was a planned addition that never was ready for release.</b><br/>
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If you're interested in ModBus support in JMRI, please
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<a href="https://groups.io/g/jmriusers">contact us on the JMRIusers list</a>.
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<ul class="snav">
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<!-- TOC -->
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<li>
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<a href="#hardware">Hardware</a>
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</li>
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<li>
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<a href="#limitations">Limitations</a>
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</li>
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<li>
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<a href="#connecting">Connecting</a>
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</li>
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<li>
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<a href="#tools">Tools</a>
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</li>
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<li>
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<a href="#documentation">Documentation</a>
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</li>
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</ul>
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<p><a href="https://modbus.org">Modbus is an industrial control system</a> that's usually
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used with pretty tough, highly-engineering equipment. The Modbus nodes are often
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"programmable logic controllers" (PLCs) which can do their own calculations of how to control
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devices.</p>
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<h2 id="hardware">Supported Hardware</h2>
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<h3>Modules</h3>
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<ul>
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<li>Modbus Nodes</li>
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</ul>
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<p>JMRI provides support for general JMRI <a href="../../tools/Sensors.shtml">Sensors</a> and
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<a href="../../tools/Turnouts.shtml">Turnouts</a> via Modbus (Node) connections.</p>
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<h2 id="limitations">Limitations</h2>
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<p><em>Modbus support is rapidly evolving; the actual code might be ahead or behind the
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documentation on any given day. Note that Modbus support is not in any JMRI test or
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production releases yet.</em>
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</p>
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<p>JMRI as Master Node is not supported yet. JMRI will eventually support operation as either
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the Master Node, or as one of the Slave Nodes.</p>
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<h2 id="connecting">Connecting</h2>
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<h3>Software settings</h3>
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<p>A Modbus installation has one Master node, and one or more Slave nodes. Generally, the
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Master writes to "Coil" objects in the Slave nodes, and reads from "Discrete input" objects
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in the Slave nodes. The "Coil" terminology comes from relay coil, solenoid coil, etc.; a way
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to change the node's output signals. The "Discrete input" is a single bit from some external
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input. By reading and writing these in a Node, a Modbus Master can sense the condition of the
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layout (through Discrete inputs) and control it (through Coils).</p>
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<h3>JMRI as Master Node</h3>
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<p><em>(There is no code support for this yet)</em>
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</p>
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<p>When JMRI is the Master Node driving a selection of remote Modbus Nodes, the net effect is
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very similar to the familiar C/MRI system. There's a Master (JMRI) that communicates with
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input (Sensors) and output (Turnouts, Lights) lines in remote Nodes. Each Modbus Discrete
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input in a remote Node gets configured as a JMRI Sensor; each Modbus Coil becomes a Turnout
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or Light.</p>
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<p>JMRI can handle multiple remote Nodes once they've been configured in the JMRI
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Preferences.</p>
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<p>There are multiple ways to configure this connection: TCP/IP vs RS485, ASCII vs RTU
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protocol, etc. Each of these requires separate code.</p>
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<h3>JMRI as Slave Node</h3>
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It's also possible for JMRI to be a Slave Node. In that case a PLC or other unit is the
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Master Node, and reads/writes JMRI when it needs to. At first, this will probably seem odd;
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JMRI is usually used as the central control for the layout. But note that Modbus is an
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industrial-strength system, and JMRI is not. If you want <em>really</em> robust railroad
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controls, you can built it using PLCs communicating with each other for operation, and only
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communicating with JMRI to display status on a Panel, get operator input, etc.<br>
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In that case, it's quite natural for JMRI to appear as a slave node on the Modbus.
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<p>When configured as a Slave, JMRI appears as Coils and Discrete inputs to the Modbus
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Master. Modbus:</p>
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<ul>
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<li>allows the Master to read and write Coils in the Slave, but can only read Discrete
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inputs; it can't write to Discrete inputs in a Slave.</li>
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<li>some popular PLC environments can only write to Coils and read from Discrete
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inputs.</li>
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</ul>
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<p>The Master Node can read from either the Coil or Discrete input for either Turnout or
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Sensor (see <a href="#naming">Naming</a> below). It can write to the Coil number to change
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the status of the Turnout or Sensor within JMRI. A "1" is THROWN or ACTIVE, respectively; a
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"0" is CLOSED or INACTIVE.</p>
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<p>Until each Coil is first written or set within JMRI, the state of the associated Turnout
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or Sensor will be "UNKNOWN" and it will be read back as "zero" on Modbus.</p>
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<p>With this convention, you can put Turnouts and Sensors on your JMRI Panel, and then
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connect them to PLC code that will tell them what to display. If desired, local changes, e.g.
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clicking on the screen, can be read back and used to control the railroad.</p>
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<h4>Configuring as a Slave Node</h4>
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In the Preferences pane for Connections, select "Modbus" as the System manufacturer and
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"RS485 ASCII Slave" as the System Connection. Under Settings, select the communications
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(serial) port your interface is connected on, the baud rate, and enter the node number your
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Modbus Master Node will use to refer to JMRI. Click "Save", quit and restart.
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<p>Next, use the Turnout Table and Sensor Table to define Turnouts and Sensors, which will in
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the process define the Coils and Discrete inputs that Modbus will read and write. Save this
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configuration to a Panel file so that it can be reloaded when you start JMRI again later.
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<h3 id="naming">Naming</h3>
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<p>The default <a href="../../../html/doc/Technical/Names.shtml">system letter</a> for Modbus
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connections is "M". It can be configured to another letter if desired.</p>
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<p>Normally, JMRI provides an interface to the real layout via internal objects such as
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Turnouts and Sensors that are closely mapped to corresponding physical devices. This mapping
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is done via "System Names", which both identify the how to access a particular device, and
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are the key to looking up the corresponding object in JMRI. Here, we have to pick a naming
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convention that allows those inside-JMRI work with the properties of Modbus.</p>
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<p>We therefore provide the following mapping:</p>
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<dl>
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<dt>JMRI Turnout MTnnn, e.g. MT123</dt>
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<dd>This will appear as Modbus coil nnn and discrete input nnn, e.g. coil 123 and discrete
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input 123</dd>
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<dt>JMRI Sensor MSnnn, e.g. MS123</dt>
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<dd>This will appear as Modbus coil nnn+1000 and discrete input nnn+1000, e.g. coil 1123
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and discrete input 1123</dd>
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</dl>
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<h2 id="tools">JMRI Tools</h2>
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N/A
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<h2 id="documentation">Documentation</h2>
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<h3>Third Party info</h3>
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<p><a href="https://modbus.org">Modbus website</a>
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</p>
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