Econet

:"This is about the network system. For the mobile phone company, see Econet Wireless."

Econet was Acorn's low-cost local area network system, intended for use by schools and small businesses. "Econet" is rumoured to be an abbreviation of Economy Network, but Acorn were always careful to stress the Greek root, "oikos", meaning "house".

Implementations

Econet was first introduced for use with the Acorn Atom and Acorn System 2/3/4 computers in 1981. It became popular as a networking system for the BBC Micro and Archimedes computers. The Econet system was eventually supported on all post-Atom Acorn machines except the Electron, the A3010 and the eventually-cancelled Phoebe 2100. The system was supported by Acorn MOS, RISC OS and RISCiX.

An "Ecolink" interface card for IBM PCs was available. It used Microsoft's MS-NET Redirector for MS-DOS to provide file and printer sharing with the NET USE command.

Acorn Universal Networking (AUN) was an early 1990s implementation of Econet protocols and addressing over TCP/IP, to provide legacy support for Econet on Ethernet-connected machines.

The Econet protocol is also supported by the Linux kernel, though it is doubtful if anyone has tried using the hardware drivers under Linux 2.6.

Physical layer

Econet is a 5-wire bus network.One pair of wires are used for the clock, one pair for data transmission and one wire is a common ground.Signalling was to the RS-422 5-volt differential standard, with one bit transfer per clock cycle.Unshielded cable was used for short lengths, and shielded cable for longer networks.The cable was terminated at each end to prevent reflections and to guarantee high logic levels when the bus was undriven.The original connectors were five-pin circular 180° DIN types, although some later Acorn RISC machines had 15-pin D-types.

Each Econet interface was controlled by a Motorola MC68B54 Advanced Data Link Controller (ADLC) chip.

Each network segment had a maximum length of 500 meters, and could have up to 254 devices ("stations").Machines and appliances such as filestores and bridges were configured with unique station numbers using jumpers or CMOS RAM settings.Network bridges, housed in a standard "BBC Cheese Wedge" box, were available for building larger networks; up to 127 segments could be bridged together.

The clock signal was generated either by a stand-alone clock box, by a BBC Microcomputer with a modified Issue 4 mainboard or by a Filestore fileserver.Only one clock generator could be used on each network.While the network was originally specified to run at 210kHz, practical clock frequencies could range from about 40kHz to around 800kHz; the presence of older machines on the network or the capacitance of a long network cable would reduce the maximum data rate reliably available.

Connections were established using a four-way handshake.The sender would broadcast.

See also

* List of device bandwidths

External links

* [http://www.heyrick.co.uk/econet/ The Econet Enthusiasts Area]
* [http://acorn.chriswhy.co.uk/Network/Econet.html Chris' Acorns]