Acorn Econet

Acorn's Econet is a networking scheme for communicating over a wired bus network between Motorola's 6854 Advanced Data Link Controllers, ADLC.

There are many websites out there which will go into far more detail than I can include here, I will be concentrating on the basics and implementations that are relevant to System (and Atom) Computers.

The Physical Network

All versions of Econet use a simple 5-wire interface comprising two wire pairs for Data and Clock and a separate Ground connection. The Data and Clock pairs are driven using RS422, typically provided by Texas Instruments 75159 driver IC. RS422 is a differential system where the data transmitted, either a Mark or Space, is the voltage difference between the two wire pair. This differs from the more common RS232 type serial interface where the data transmit and receive signals are sent over separate wires referenced to ground.

All the devices on the network share the same Clock and Data and are joined together in a continuous run, with no branches, using various interconnection devices including T-sockets, Socket Boxes and Hubs.

The cable used should ideally be of shielded twisted pairs with a nominal impedance of 100ohms, for large networks this will be important but for small networks you can certainly get away with less. Interconnections are made using 5-pin 180 degree DIN plugs (some later Acorn machines used different connectors).

	Pin	Function
	1	DATA+
	2	GROUND
	3	CLOCK+
	4	DATA-
	5	CLOCK-
Connections are for a socket viewed from the front

Network Clock & Terminators

In an Econet network the Stations require a Clock to synchronise their transmissions, this is provided by a separate unit which is ideally connected near the mid-point of the network, in addition each end of the network should be fitted with a Terminator.

Clocks and Terminators were available from Acorn as well as other suppliers some of which are detailed here: Econet Clocks & Termination.

Econet Protocol

The underlying Econet protocol defines how connected devices, known as Stations, are addressed and how sharing of the network is managed. There have been a number of different versions or Issues of Econet:

Issue 1 Econet - this uses an 8-bit Station ID and 16-bit addressing but has no collision arbitration but had package acknowledgement
Issue 2 Econet - was an attempt at reducing the overhead of the package acknowledgment but it was found to be unreliable
Issue 3 Econet - reinstated the acknowledge packet, increased the size of the Station ID to 16-bits and addressing to 32-bit
Issue 4 Econet - not really a different protocol but refers to an improved implementation of the firmware

Network Filing System NFS

A Station is fitted with a Network Operating System or NOS ROM (also known as the Network Filing System or NFS on the BBC). The NOS provides the interface to Econet in a similar way that the COS or DOS provide interfaces to cassette or floppy disk storage.

The NOS actually contains two software elements, in addition to the Filing System it includes what are known as the Econet Primitives. This is the code that interfaces with the hardware and performs the basic transmit and receive function. It is not visible to the user being accessed either by the Filing System or from a program via OS calls.

When the NOS is activated it will report the versions of the two components (System/Atom computers only) e.g.:

NOS V.IIIO

Econet 3.40

where ‘V.IIIO’ is the filing system version and the ‘3’ in ‘3.40’ refers to the Econet Issue in this case Econet 3.

The following table lists all the copies of NFS for the System/Atom Computers that I have been able to find, clicking on the link will download the ROM image. I have also included BBC Computer NFS versions because they are useful if you want to set up a BBC as e.g. a File Server.

(The Econet interface on an Atom is electrically the same as a System Computer and therefore an Atom uses the same version of NFS as System Computers.)

Name	Platform	Size	Econet	NOS (NFS)	Comments
NFS 1.48	System/Atom	4K	1
NFS 2.40	System/Atom	4K	2	V.IIH
NFS 3.40	System/Atom	4K	3	V.III0
NFS 3.50	System/Atom	4K	3	V.IIIP
NFS 3.34	BBC	8K	3
NFS 3.35	BBC	8K	3
NFS 3.60	BBC	8K	3		The standard NFS upgrade for the BBC B
DNFS 1.20-3.60	BBC	16K	3		Also includes DFS 1.20 for 8271 FDC)
ANFS 4.18	BBC	16K	4		Performance benefits over 3.60 but at the expense of memory both ROM and RAM

File Servers

A range of File Servers were available from Acorn and other suppliers with different capabilities or 'Level', some are programs that run on a System or BBC Computer platforms whilst others are bespoke units.

It is important to be aware that File Server Level has nothing to do with Econet Issue they are different things though the File Server must be the same Econet Issue as the User-Station i.e. an Econet 3 Level 2 File Server must be used with User-Stations that are also Econet 3.

Follow the links for further details of each File Server.

Acorn Level 1 File Server

This Server offers very basic facilities that allow files to be loaded, saved and catalogue and that's about it. It is a Basic program that runs on a BBC B Computer.

It is however very easy to get up and running so is a good starter when trying out Econet for the first time.

The Level 2 and 3 File Servers offer much improved features including random access and security controls, the Level 3 server adds time/date stamping and performance improvements.

Acorn Level 2 File Servers

Acorn Level 3 File Servers

Acorn's FileStore is a family of dedicated Level 3 File Server machines with built-in floppy disk storage and the option of add-on hard drives.

Acorn FileStore

Bridges

Acorn Econet Bridge

Econet Documentation

I have gathered several Econet documents which you can get from here:

Back to Filing Systems

Acorn Home Page