THE MAGAZINE FOR COMPUTER APPLICATIONS
Circuit Cellar Online offers articles illustrating creative solutions
and unique applications through complete projects, practical
tutorials, and useful design techniques.

The eZ80 Webserver

An 8-Bit CPU Takes on the Internet

by James Antonakos

Start ý Software Model ý Memory Map ý Instruction Set ý On-Chip Peripheral Registers ý Hardware Architecture ý TCP/IP Stack Operation ý eZ80 Evaluation Board ý Connecting the System ý Developing the Hardware and Software ý Application: A Web-Based Security System ý Other Applications ý Win Your Own! ý Sources and PDF

APPLICATION: A WEB-BASED SECURITY SYSTEM

Several years ago, my department moved into a new building on campus. At the request of the faculty and staff, all the doors on our floor are wired with switches. The wires to all the door switches terminate in an electrical panel in our digital electronics laboratory. Adding pull-up resistors and debouncing logic allows us to generate a one or zero state for each door on the floor. A 24-bit programmable I/O card plugged into a personal computer together with some custom multiplexing circuitry provide two banks of 16 input bits, or enough for 32 doors.

Software to read the door states and decode them was initially written in BASIC, then rewritten in 80x86 assembly language, rewritten again in C, and finally ported to Visual C++. Using a networked drive, the software dynamically creates web pages reflecting the state of the doors and posts them to the college web server.

My goal is to eliminate the personal computer controlling the security system and replace it with the evaluation board. I plan to create a new web page for the security system, which will be hosted by the eZ80. Iýll interface the existing input logic to the evaluation board, add a seven-segment display module (for indicating room numbers and open/closed condition), remount everything (including a new power supply) in the electrical panel, download the security code, and let it run.

I spent an afternoon working on the new web page and learning how to use the Zilog development system compiler. I started by building the demo that comes with the system. I learned that HTML files, and even GIF and JPG image files, are converted into C code by the compiler. This code gets compiled and downloaded into the evaluation board RAM. With 1 MB available, a rich set of web pages can be stored in RAM.

As indicated in Photo 3, I successfully built and downloaded my new web page. Note the IP address of the evaluation board (172.16.1.5). This IP address is an internal network address at my school and is not visible to the outside world. The default IP address is 192.168.1.1, but this can be changed in the software.

(click here to enlarge)

Photo 3ýHere you can see a screen shot of the embedded web page hosted by the eZ80.

Anyone interested in following my progress on the security system upgrade can visit www.sunybroome.edu/~antonakos_j/ez80.

PREVIOUS • NEXT