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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

READYýSET?

The modem is ready, but before you fire off any phone numbers, the S-7600A must be told that PPP mode will be used and the authentication method will be PAP. Then all of the data entered into the EEPROM via the Menu function in Photo 4 (with the exception of the phone number) is retrieved and placed into the appropriate S-7600A registers. The username and password are written into the S-7600A PAP string register. The length of the field precedes the actual data. For instance, if the username is Fred, a 0x04 is written to the PAP register first followed by Fred in consecutive ASCII characters. When all of the user data is entered, a final NULL character (0x00) is written to the PAP string register.

The next step is to issue the ATDT modem command followed by the ISP phone number entered earlier. The PIC16F877 has control of the S-7600A UART and is responsible for issuing the dial command. With some extra command work up front, you can configure the US Robotics modem to give you result codes during the dial process. I chose to simply wait for a connection, as the US Robotics modem has a built-in speaker and I wonýt be putting this S-7600A/PIC16F877 Internet Engine out in the real world. I arbitrarily set the wait time for 20 s, which should be long enough for a connection to be established at 2400 bps. You should write some code to track modem and line status if you plan to deploy your S-7600A/PIC16F877 Internet Engine in the field.

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