Internet connectivity:
The time is right and the technology is ready for you
By Olaf Pfeiffer and John Rodrigues
[ Introduction
| Internet Connectivity Parameters | Case
Study ]
[ Adapting
the Software | Dynamic Web Pages | Feedback
with Forms ]
[ Continuous Refresh | Security
| Summary ]
| < Previous Page |
Continuous Refresh
By now, the user can view dynamic data from the embedded device and send data to it. However, all communication is user-driven in that the user needs to initiate every request. Wouldn't it be nice to see a window constantly updating / refreshing itself with the dynamic data from the embedded device without the need of user intervention?
If one refresh every few seconds is sufficient, the HTML REFRESH tag can be used to make the browser refresh the display automatically every few seconds by re-requesting the Web page. However, this causes overhead issues as the entire Web page gets transferred every time (also the static part) and it does not allow faster updates.
A faster, more efficient window refresh cycles can be achieved using Java. A Java applet can establish an additional TCP/IP channel between the host computer and the embedded Web server. As the implementation of this TCP/IP channel is customized on both ends of the communication, it can be highly optimized to transfer only the required data.
In this application, we used it to transfer all the data from the CAN/CANopen network in the embedded device and the Java applet implements a basic CAN monitor that constantly displays all the CAN/CANopen messages in the Web browser. See figure 2 for a screen shot showing the result.
Figure 2 Java Applet Screeshot
showing CAN bus messages
| < Previous Page |
[ Introduction
| Internet Connectivity Parameters | Case
Study ]
[ Adapting the Software
| Dynamic Web Pages | Feedback
with Forms ]
[ Continuous Refresh | Security
| Summary ]
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