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AN S-7600A/PIC16F877 JOURNEY

Part 2: Revving It Up
by Fred Eady

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

GO

After the PIC16F877 is notified that the physical connection to the ISP is established, the PIC is responsible for passing the ball to the S-7600A. This is done by setting the Connection Valid bit in the S-7600A PPP control and status register. Setting this bit tells the network stack that the layer below it is up and operational. The Use PAP and PPP enabled bits also reside in the PPP control and status register and are set with the same command used to signal a good connection to the ISP. If you follow WWII movies, this is where the pilot of the B-17 turns over control to the guy with the Norden bombsight. The PIC sets the SCTL bit in the serial port configuration register and gives control of the S-7600A UART to the Seiko IC and its network stack mechanism.

This is the point in the process where the S-7600A performs its magic. Iıve taken a full snapshot of the process using Serialtest Async. Iım providing it to you as a readable file so you can follow through the PPP negotiation sequence frame by frame, beginning to end. The only information Iıll censor is my logon password. Iım also including an Acrobat file that contains the Serialtest Async frame decodes. Using the ASCII file in conjunction with the PDF file will illustrate the total PPP process.

Bit 0 of the PPP control and status register confirms to the PIC16F877 that PPP is up and operating. Your ISP assigned IP address is negotiated and Photo 8 is the Tera Term Pro view of the result.

Photo 8ıThe IP address is the address given to the S-7600A by my ISP during PPP negotiation. Socket open indicates that the S07600A has passively opened a socket for listening on Port 80.

The S-7600A/PIC16F877 Internet Engineıs PIC16F877 code has now entered the web server loop area. The code here checks PPP up status and the condition of the modemıs DCD pin to determine if the link is up and functioning. The S-7600A is capable of supporting two sockets. This web server application uses Socket 0. Because the S-7600A/PIC16F877 Internet Engine is serving, Port 80 is loaded into the S-7600A, the server mode is activated, and Socket 0 is brought online.

If no timeouts occur and the link remains active, a request from a remote web browser can be fielded. S-7600A socket status is interrogated to ensure that a good connection exists and that the TCP state is listening. If a request is received from a web browser, an HTTP header is constructed and transmitted followed by the HTML stored in the 24LC256 EEPROM. Time and temperature are obtained from the DS1629 and inserted into the HTML text. The assembled HTML page is then sent to the S-7600Aıs socket data register. The data is sent and the PIC16F877 waits for the transmit to complete. The socket is then closed and reopened making it ready to serve yet another page of HTML like the one shown in Photo 9.

Iıve shown you how to take an everyday PIC, a C compiler, a tiny firmware protocol stack, and a handful of common components and put them on the Internet. For those of you who wish to build and experiment with your own S-7600A/PIC16F877 Internet Engine, Iıll post the details of how to purchase the kit at www.edtp.com.

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