HyperText Transfer Protocol (HTTP) is a standard Client/Server Internet protocol that transfers web content over a TCP/IP network. The Programmable Logic Controller (PLC) with an Ethernet module acts as an HTTP Server (web content provider), which responds to requests from HTTP Clients (web browsers). The PLC supports HTTP Client authentication, requiring the web browser to enter a Username and Password, before web content can be accessed. Properly authenticated, an HTTP Client can access web content previously stored in the PLC file system. This web content can include standard static HTML files and other web resource files. (images, sound, etc.) In addition, the PLC HTTP server allows the HTTP Client to display and edit PLC register data, by embedding specially named dynamic HTML files into a static HTML file.

To start browsing web resources stored in the PLC file system, enter the appropriate Uniform Resource Locator (URL) into the HTTP Client (web browser). As a minimum, the URL should include the target PLC’s IP address and a filename. For example, if the PLC’s IP address is, the following URL will access the PLCscene.htm file in the PLC file system root directory:

If the Ethernet module was configured with a Username and Password, the browser will prompt for the Username and Password to be entered, before opening the web page (PLCscene.htm).

A PLC HTML file is either static or dynamic. These files can be created with a simple text editor or by using a 3rd party HTML Editor. To specify the PLC register to read or write there are two parameters required; reference and format. The required register parameter is a number with a maximum limit, depending on the PLC register type. (Input, Output, etc) Valid format types are Boolean, Binary, Hex, Integer, Real and ASCII.