Acorn Econet

Econet is the local area networking system for BBC Micro computers. To relive our childhoods, we're going to build an Econet at the lab.

• Econet clock unit. One required for each network, to generate the timing signal. We can buy this for £50, or make it ourselves with reasonably basic components.
• For each BBC Model B client: a kit of components to be soldered onto the motherboard. Kits can be bought for £30, or we can source the parts ourselves (though one IC is very rare).
• For each BBC Master: an Econet daughterboard and ROM. Cost is £30. We can also use an Archimedes Econet board available for £10, and burn our own ROM.
• M-M 5-pin DIN (180 degrees) cables. One per client, and one between each junction box. MIDI cables can be used, as long as they are fully-wired (all 5 pins).
• Passive terminators (male 5-pin DIN with some resistors/capacitors). One at each end of the chain.
• Junction boxes. Three or more DIN sockets connected in a short-chain. The backbone (or terminator) is connected at either end of the chain, and one or more clients connected in the middle.
• File server: Level 1 (very basic) can be run on any BBC with a floppy. Level 2-3 require a second processor (which we have). Archimedes can also act as a file server with some free software.

Option 1: Aftermarket and fully configurable clock from BeebMaster. £50.

Option 2: Econet hub circuit from Mark Usher, incorporating workstation junction and terminators. Clock duty cycle is fixed at 50%.

Option 3: Build our own clock with an ATtiny and a differential driver IC. Would need to consider the maximum speed at which the ATtiny could maintain a clean clock signal. If we take this option, Tim suggests building it into a hub unit with 4-5 sockets (2 passthrough and 2-3 workstation), but keep the terminators as separate plug-in components.

5-pin Male to 5-pin Male. One is required for each workstation to connect to a junction, and one between each junction.

Tim recommends buying some cheap ready-made cables from ebay (usually sold for audio or MIDI applications). Make sure that the cables have all 5 pins fully-connected.

We can make our own cable if we need to link further than 5M (e.g. across the length of the lab).

We should also consider whether to span between G1 and G8. It should be possible to use the spare CAT5 port next to galahad and patch that into G8.

Tim has a stock of 6-core shielded cable that would be suitable for custom cables.

A passive design, suitable for building into a 5-pin DIN plug, is available:

http://www.retro-kit.co.uk/page.cfm/content/Passive-Econet-Terminators/

We will probably need to purchase 1/4W resistors as most of our stock is 1/2W.

We would require two terminators, and consider making a spare.

Tim has ordered a 5-pack of Econet modules for BBC Master or Archimedes.

We will burn our own ANFS EPROMS.

To show-off our network, we'll want to host some applications.

• Games archive (Elite, Repton, Granny's Garden, …)
• Multiplayer games
• Hacklab Teletext
• Telnet/SSH (this won't be trivial)