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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

TERA TERM PRO

This terminal emulator adds class and a bit of automation to the boot loader PIC code. I assembled a simple macro program to run under Tera Term Pro (see Listing 2), which guides you through the S-7600A/PIC16F877 Internet Engine file upload process. Basically, the Tera Term Pro macro (upload.ttl) connects to the S-7600A/PIC16F877 Internet Engine via a personal computerýs COM2 serial port and uploads code to the PIC16F877 by way of the boot loader code.

Letýs analyze the macro beginning with the definitions area. Tera Term Pro uses message boxes that look like their standard Windows counterparts to communicate with you. The boxtitle defines the text that resides in the title area of the message box. The rest of the definitions in this area are the wording that will appear in message boxes called from various parts of the macro. The only exception is uploadfile, which is actually the Intel hex file that is loaded and executed. In my macro, this file is called seiko.hex and is actually the web server code.

Moving on to the main macro code area, you find the label :begin followed by a connect command. The /C=2 tag says connect to the personal computerýs COM2 serial port. The connect command returns a result code. If the result code is 0, a link to Tera Term Pro has not been made. A result code of 1 means the link to Tera Term Pro is good but there is no connection to the host. You want a result code of 2, which tells you that the link to Tera Term Pro and the connection to the host are up.

Result codes of 0 and 1 trigger a messagebox event that informs you of the error and disconnects Tera Term Pro. A result code of 2 causes the macro code to branch to the :goodlink label. A yesnobox is triggered asking if you would like to upload code to the S-7600A/PIC16F877 Internet Engine.

If you glance at the boot loader listing, youýll see that an ASCII "u" activates the upload portion of the code. A yes tells Tera Term Pro to send the ASCII "u" to the boot loader code and wait for the outcome of the upload process. The S-7600A/PIC16F877 Internet Engine boot loader code will send an ASCII "g" if the upload is good and an ASCII "E" if any of the checksum calculations donýt match the original line-by-line checksums.

As you can see in the macro listing, a "g" is result code 1 and the "E" is result code 2. This is determined by the order of the ASCII characters behind the wait command. A no answer to the upload question simply keeps Tera Term Pro connected and nothing else. The boot loader will time out and attempt to run the boot vector code.

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