The Spectranet is an Ethernet card for the Sinclair ZX Spectrum computer platform, though don't be deceived by its name, as it's a bit more than just a simple Ethernet card. The device contains a 'network operating system', with a socket library very similar to the BSD [socket library] you'll find on Unix/Linux, Windows, Mac OS X (and of course BSD). It contains a network file system, and support for BASIC channels and streams, so the BASIC programmer can write networked programs as well as those who know the more versatile C or Z80 assembly language.

The Ethernet hardware is based on the Wiznet W5100 chip, which is designed for 8-bit systems. These days, this means micro controllers and small embedded systems in general, but it's perfect for the old Speccy. It supports both 10baseT and 100baseTX, full and half duplex, and access to the hardware is memory mapped rather than I/O mapped.

There's a CPLD (basically, today's ULA chip) that provides the logic functions such as memory management, the I/O ports and execution trapping to automatically map the Spectranet memory into the lower 16KB of address space when library calls are made (in this part of RAM, there are four 4KB pages). This allows software to provide a system of modules, so that functions of the peripheral can be easily expanded with new pieces of software. This can be accessed from the Spectrum, because the Spectranet ROM is provided by a 128KB flash chip, to which the host machine has complete read-write access.

To allow more space for programmers, there's also 128KB of static RAM. Some of this is dedicated to system variables and temporary workspace, but most of it - is available for programmers. The printed circuit board is a four layer board to get the best electrical performance from the CPLD and W5100, and also to keep the size of the card small enough that it's feasible to put the through port on the back of the card (rather than needing a more mechanically complex through port connector like what you may find on the Interface 1 or other similar Spectrum add-on). Of course, I could tell:you more, but we're about to run out of editorial column inches. I'll conclude my introduction next week.

It's been a while since we've done it, but we can't talk about the Spectrum again without giving a shout out to the extraordinarily good World Of Spectrum website. Regularly updated, and the home of thousands upon thousands of files to download and run on an emulated Spectrum, it's found at www.worldofspectrum.org