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:// 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.

plc4x architecture


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

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