Q What is a CAN bus sys­tem?

Motorcycle News (UK) - - Garage -

Richard Red­mayne, Dyno­jet UK This is a term you hear a lot when it comes to modern bike elec­tri­cal sys­tems. ‘CAN’ stands for Con­troller Area Net­work and ‘bus’ is a trans­mis­sion path for trans­fer­ring data on a sys­tem, which early com­puter designers thought was sim­i­lar to a bus mak­ing mul­ti­ple stops on a route.

CAN bus was de­vel­oped by Bosch in the 1980s and first ap­peared in bikes when BMW fit­ted it to their K-se­ries ma­chin­ery with the first anti-lock brakes. Tra­di­tion­ally bikes have a multi-wire wiring loom to in­ter­con­nect var­i­ous elec­tronic com­po­nents on in­di­vid­ual cir­cuits.

A CAN bus sys­tem gets rid of that huge bun­dle of wires for one or two twisted wires con­nect­ing var­i­ous Elec­tronic Con­trol Units (ECU) or ‘nodes’, saving space and ma­te­ri­als for a cleaner way of trans­mit­ting data with no loss of in­tegrity. On a bike those nodes could be ECUS for the anti-lock brak­ing, dash, trac­tion con­trol, ride-by-wire throt­tle and elec­tronic sus­pen­sion; a Du­cati Mul­tistrada 1200 has six nodes.

The ba­sic prin­ci­ple is that each node can send and re­ceive mes­sages, but not si­mul­ta­ne­ously. Those data mes­sages have dom­i­nant and re­ces­sive bits, and depend­ing on its pro­gram­ming, when a node is in ‘lis­ten’ mode it can iden­tify if the net­work mes­sage has pri­or­ity and is rel­e­vant, so there’s no delay in the higher-pri­or­ity mes­sage, and the lower-pri­or­ity mes­sage is au­to­mat­i­cally re­trans­mit­ted.

How­ever, this ‘in­tel­li­gence’ means that it can be tricky adding after­mar­ket com­po­nents as the CAN bus will sense an ad­di­tional power feed as an in­ter­rup­tion in the data stream, and throw up an er­ror code. But if you can find a way in, for ex­am­ple on BMW GSS you can take power from the COM port, then it doesn’t mind. It de­pends what it’s pro­grammed with at the fac­tory.

First seen on BMWS, CAN bus sys­tems keep heavy wiring to a min­i­mum

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