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Ethernet on a Chip

Ethernet on a Chip

Fred describes his recent work with the ASIX Electronics AX11005 development kit. Using a Keil C compiler and some Digital Core Design hardware, he created a powerful Ethernet development suite that now enables him to produce some pretty exciting Ethernet-based equipment.
The AX11005 is designed to do a bit more than just service Ethernet frames. The core of the AX11005 is a fast (up to 100 MHz) 100% binary-compatible clone of the venerable 8051. The 19-bit flat program addressing mode uses the 80C390 instruction set to enable bankless 0- to 512-KB access of on-chip program flash memory. The AX11005 can also execute instructions using 16-bit large program addressing mode, which calls on the 80C51 instruction set. A 16-KB SRAM area is used for program flash memory mirroring. In addition, 32 KB of on-chip user SRAM is allocated in the external data memory area.

It almost seems as though the AX11005’s 10/100 Ethernet capability is an afterthought because the microcontroller supports a 1-Wire interface, three RS-232 ports, I2C, PWM, counter/timers, three SPI masters, a SPI slave, and 16 bits of general-purpose I/O. The idea behind the multitude of communications interfaces is to put the AX11005 into an application space that can convert RS-232 serial data to Ethernet frames or communicate with a ZigBee radio via the SPI port and bidirectionally transfer data between the ZigBee PAN and Ethernet link. With its many ways of communicating, the AX11005 is powerful enough to act as a network processor serving other link-attached or physically attached microcontrollers.

A single 3.3-VDC power source powers the AX11005. Keeping with the system-on-a-chip (SoC) concept, an on-chip 1.8-VDC regulator feeds the CPU core. The AX11005 requires only a single 25-MHz crystal for all of its internal clock generation processes. There’s even a built-in, on-chip, power-on-reset circuit.

The AX11005 will most likely find itself embedded in an install-it-and-forget-about-it environment, so simple methods of upgrading the SoC’s firmware must be available. The AX11005 can accept updates by way of the Ethernet port or the UART. You can also use the UART to program the device.

I’m particularly interested in the TCP/IP offload engine (see Figure 1). But before I delve into that, let’s look at what it takes to support the AX11005.

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