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Introduction to Read and Write PLC Variables Via HTTP Interface

The PLC"Programmable Logic Controller" A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Used to synchronize the flow of inputs from (physical) sensors and events with the flow of outputs to actuators and events variable interface provides following features and advantages:

• A simple HTTP interface is used to read/write PLC variables.
• Multiple variables can be read /written in single HTTP request at the end or start of a PLC cycle.
• Quick application development. The interface allows a user to quickly develop applications in many languages (such as Java, C#, and C++).
• Platform independence. Applications can be developed on any platform supporting HTTP.
• Remote access. Variables may be read/written from a remote machine.
• Security. There is an Authorization mechanism which enables access to the interface. For information on how, see "Configure the Controller".
• Support for both JSON and text (raw) formats to send/receive requests or responses. The format is detailed in the following sections.
• Support for all basic PLC data types:

  BOOL	SINT	USINT
  BYTE	INT	UINT
  WORD	DINT	UDINT
  DWORD	LINT	ULINT
  LWORD	REAL	LREAL
  TIME	STRING

  The individual array elements and structure members can also be read/written by using formats explained in the following sections.

There are two interfaces:

• A variable READ interface which is used to read a set of PLC variables.
• A variable WRITE interface which is used to write a set of PLC variables.

The URL is same for both interfaces: (controller URL)/kas/plcvariables

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