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AN S-7600A/PIC16F877 JOURNEY

Part 2: Revving It Up
by Fred Eady

Start ý Tera Term Pro ý Road Test ý The Hardware ý As a Web Server ý Branching Out ý Making Changes ý ReadyýSet? ý Go ý Sources and PDF

For the last couple of weeks, Iýve been chasing bits all over the Florida room. The S-7600A/PIC16F877 Internet Engine is purring, and in this installment, Iýll take you all the way through using it as a web server. However, before I begin the technical discussion, there are some things I need to fix from last month.

The boot loader has been revised to fix some bugs and make it easier to use. The PCW builds an Intel hex file and appends the whole thing with a semicolon followed by the PIC type the file is intended to load into. That semicolon and the text that followed it drove my boot loader menu crazy. The problem was that the boot loader code didnýt know that the characters following the last Intel hex line were bogus. It tried to load and analyze them. So, I simply turned off the PICýs serial receiver in the UART and delayed long enough to allow Tera Term Pro to spout all of the leftover junk characters beginning with the semicolon.

A second potential problem involved the boot code vector area. If for any reason the Tera Term Pro download failed, the boot code vector for the failed program would be retained in the NOPs area. If the S-7600A/PIC16F877 Internet Engine was allowed to restart, it would vector to nonexistent or corrupted code. To avoid this, I rewrite the boot code vector area with NOPs if the download fails. This allows the boot loader to loop and wait until valid code and a valid boot code vector are loaded. I also cleaned up the boot loader listing to make it easier to follow. The results can be seen in Listing 1.

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