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:imagesdir: images/

== About PLC4J

`PLC4J` is a sub-project of `PLC4X` with implementations based on `Java` targeted at runtimes for `Java 1.8` or above.

One of PLC4X's core principals is, that an application using PLC4X should be independent of the PLC or protocol being used.

When addressing a resource on a remote there are two parts that are dependent on the protocol and the type of PLC:

- Addressing the PLC itself
- Addressing a resource on the PLC

Providing this independence to addressing the PLC itself is completely handled by the `PlcDriverManager` the application requests a connection from.

Hereby the design of the `url string` passed to the `getConnection` method is greatly inspired by `JDBC`.

The protocol prefix of the url specifies the type of driver being used.

For example, when connecting to a Siemens PLC using the S7/Step7 Protocol, the url: `s7://192.42.0.98/1/2` causes the driver manager to create a S7 connection instance.
The part behind the `:` is hereby used by the driver implementation to configure that particular connection.

For a S7 connection, for example, this is `IP address/host name`/`rack number`/`slot number`. For different types of connections this url structure will greatly differ.

As mentioned above, the second platform dependent information is the address of resources on a PLC.
The format of an address greatly depends on the type of connection. Therefore `parseAddress` is one of the only methods defined in the `PlcConnection` interface any connection has to implement.

This method returns an object implementing the `Address` interface which then can be used by the same connection to identify remote resources.

[ditaa,plc4x-architecture]
....
+----------------------------------------------------------------------------------------------+
|c05A                                                                                          |
|                                                                                              |
|                              User Application                                                |
|                                                                                              |
|                                                                                              |
|                  +-----------+------------------+------------------+------------------+------+
|                  |           |                  |                  |                  |
|                  |           |                  |                  |                  |
|                  |           v                  v                  v                  v
|                  |    +-------------+    +-------------+    +-------------+    +-------------+
|                  |    |c0BA         |    |c0BA         |    |c0BA         |    |c0BA         |
|                  |    |   Apache    |    |   Apache    |    |   Apache    |    |   Apache    |
|                  |    |   Kafka     |    |    Camel    |    |   Edgent    |    |    Nifi     |
|                  |    |   Connect   |    | Integration |    | Integration |    | Integration |
|                  |    |             |    |             |    |             |    |             |
+---------+--------+    +------+------+    +------+------+    +------+------+    +------+------+
          |                    |                  |                  |                  |
          |                    |                  |                  |                  |
          v                    v                  v                  v                  v
+----------------------------------------------------------------------------------------------+
|cAAA                                                                                          |
|                                                                                              |
|                                             PLC4X API                                        |
|                                                                                              |
|                                                                                              |
+------+---------------+---------------+---------------+---------------+---------------+-------+
       |               |               |               |               |               |
       |               |               |               |               |               |
       v               v               v               v               v               v
 +-----------+   +-----------+   +-----------+   +-----------+   +-----------+   +-----------+
 |c0BA       |   |c0BA       |   |c0BA       |   |c0BA       |   |c0BA       |   |c05A       |
 |  Siemens  |   | Beckhoff  |   |  Modbus   |   |  OPC UA   |   |  Emerson  |   |   User    |
 |    S7     |   |   ADS     |   |  Driver   |   |  Driver   |   |  DeltaV   |   |  Driver   |
 |  Driver   |   |  Driver   |   |           |   |           |   |  Driver   |   |           |
 |           |   |           |   |           |   |           |   |           |   |           |
 +-----------+   +-----------+   +-----------+   +-----------+   +-----------+   +-----------+
....

=== Usage

Below code example connects to a remote Siemens S7 PLC using the S7/Step7 protocol and then reads the state of the `inputs` and `outputs` from this.

It also demonstrates two ways this information can be accessed:

- Synchronously (The application pauses, till the response is received)
- Asynchronously (The application continues and can

[source,java]
----
include::../../../examples/hello-world-plc4x/src/main/java/org/apache/plc4x/java/examples/helloplc4x/HelloPlc4x.java[lines=19..200]
----

