Embedded web servers - a solution to configuring embedded devices
September 2001
Fieldbus & Industrial Networking
Sean McCree
The Internet has impacted on the modern world to such an extent that the ability to browse websites and download information has become the norm. The expectation to access any device via a web browser has led to many manufacturers adding web capability to their products.
Industry today
In the past, configuring and monitoring data from an embedded device has often proved to be a difficult exercise, as traditionally, data has been transferred serially using a protocol derived from RS232 and RS485. An application is loaded on a PC, and the raw data is transferred across the serial connection. Aside from distance limitations, and data transfer rates, suppliers are faced with the software development costs of upgrading their software for different operating systems, and users are required to install software they may not always require on the same PC.
The widespread use of TCP/IP, and the expansion of Ethernet-based local and wide area networks has brought a solution as many of these problems can be solved by including a web server as part of the embedded device. Now, by using HTML as a standard development language, the embedded device can display the same data with any commercial web browser. The user can now comfortably sit in his office or at home, and using a TCP/IP connection over the Internet, monitor and modify the configuration of his embedded device anywhere in the word.
Communication
For an embedded device to be web-enabled, it has to have a web server running that may be accessed by an external web browser over a network connection. The protocol used between the browser and server is HTTP (Hyper Test Transfer Protocol). As HTTP runs over TCP/IP, the engine of the web server is the TCP/IP stack, which is responsible for the transfer of data from the application, across a physical Ethernet link. User accessible web pages are stored within the web server. The web server thus handles requests from the browser to access these pages and passes data to and from the browser.
When a web browser retrieves a file from a web server, the server provides the MIME (multipurpose Internet mail extension) type of the file. The browser uses the MIME type to establish whether the file format can be read or, if not, a suitable application is available to read the file.
Typical web-enabled embedded devices will consist of a web server as well as an application running on the device. The web server thus provides an interface between the web browser or the user, and the application running on the embedded device.
The solution
The EtherMOD range of thin servers provides an innovative method of implementing web servers on existing embedded devices. Essentially, the EtherMOD enables the connection of any TTL serial device with an Ethernet network. It is programmed with an IP address, subnet mask and gateway address compatible with the network it is planned to connect with. When the EtherMOD is running, it becomes 'transparent', passing data to and from the serial device to the application. The EtherMOD also contains a web server, and can thus be remotely fully configured using any commercial browser. Using FTP, client-specific HTML pages can be loaded onto the EtherMOD, and a scripting functionality allows for the display and manipulation of serial data from these web pages. Effectively, the set-up and monitoring software applications mentioned earlier can be completely replaced by web browser functionality, eliminating the need for loading software on any customer machines. In addition, the user interface can be upgraded using FTP.
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