Electronic Design

TCP/IP For 8- And 16-Bit Devices

Cost-sensitive Internet appliances provide a great home for 8- and 16-bit processors, especially when only limited TCP/IP support is required. Many applications work well with a compact Web server and limited resources. Different approaches are available for providing TCP/IP support.

The conventional approach is the compact TCP/IP stack that has a limited feature set. Another approach, Internet Modem, is available from ConnectOne. This approach uses a byte stream interface with commands that are similar to the Hayes-compatible modem commands.

The serial modem approach is interesting because a number of embedded solutions using TCP/IP are connected to other devices using a serial link, often via a modem and a telephone line. Ethernet is more popular, but wireless, HomePNA, and HomePlug systems are on the rise.

Compact TCP/IP Stacks
Advantages

  • Work on almost any processor
  • May operate in polled mode
  • Can operate without an OS

Disadvantages

  • Limited functionality
  • Limited security and encryption
  • Performance limited by hardware

These features can be found on a number of compact TCP/IP stacks, such as those available from CMX. The CMX TCP/IP stack can fit on 8-bit processors, along with a 20-kbyte Web server. The amount of information that can be delivered will be limited by processor memory, but it will work with any Web browser.

Compact stacks often use a custom API instead of a larger and more functional interface, such as BSD sockets. In many cases this is of little consequence because developers deal with Web servers and other services.

Internet Modem Commands
Advantages

  • Simple application interface
  • Support coprocessor interface

Disadvantages

  • Limited functionality
  • Proprietary interface
  • Limited by serial interface

ConnectOne's Internet Modem uses a text stream interface that operates in a fashion similar to a Hayes-compatible modem via a serial interface. Instead of prefixing command strings with AT, the Internet Modem protocol starts with AT+i. Commands can send or receive e-mail, access Web pages, and work with most Web-based applications.

The Internet Modem protocol has been implemented in a coprocessor that can be easily coupled to an 8- or 16-bit processor. A software implementation is available for a number of processors, making the Internet modem a portable solution.

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