Chapter · CAN bus
The hall
Why one pair, what a state is on two wires, labels instead of addresses, who speaks first, and how every desk stays in step with no clock wire.
- 01Why one pair, and what the hall gets wrong4 minWiring every device to every other takes a cord for each pair of them. CAN gives them all one pair of wires instead, and nobody is in charge of it. The hall used in this course is only a picture of that.
- 02Two wires, one state4 minA CAN bus is in one of two states, set by the difference between its two wires. Noise that lifts both wires together leaves the difference alone, which is why there are two.
- 03Labels, not addresses4 minA CAN message does not say who it is for. It carries a label saying what it is, every device hears it, and each device decides for itself whether to use it.
- 04Who speaks first4 minWhen two devices start together, they sort it out bit by bit while sending the label. The lower label wins and the winner loses nothing. The loser waits and tries again.
- 05Staying in step4 minThere is no clock wire. Each device has its own oscillator and recovers the timing from the edges on the rail, restarting on the first edge of a message and nudging on the rest.
Start at 01 and read down — the order is the order things get easier in. Or take the one with your part in it; every article stands on its own, and links back to whatever it needs.