Wiring, termination and load

This is the chapter that matters on this product. The firmware needs almost no configuration; the installation does.

The two connectors

Connector	Goes to	Speed
CAN 1	one MUXEN segment — normally the side the Brain is on	500 kbit/s
CAN 2	the other MUXEN segment	500 kbit/s

Both are MUXEN buses. Unlike every other CanCan, CAN 2 here is not an equipment bus: it speaks the same protocol, at the same speed, as CAN 1. The two are interchangeable as far as the firmware is concerned — nothing behaves differently depending on which segment a device is on. Calling one of them "the Brain side" is a convention for the installer, not a rule in the box.

Neither speed is configurable. 500 kbit/s is fixed in the product's firmware build; there is no parameter, and no muxen-uds command, that changes it.

Termination: four resistors, not two

This is the single most common error on this product.

The extender does not splice the two segments into one piece of wire. It is a node with one bus interface on each side, and each side is a complete, independent CAN segment. So:

Each segment carries one 120 Ω termination at each of its two physical ends. Two segments means four terminations on the boat.

If you terminate the pair as though it were one bus — one resistor at the far end of segment A, one at the far end of segment B — each segment is left half-terminated. The symptom is not a clean failure: it is a bus that works on the bench with short cables and produces intermittent errors, dropped frames and devices that come and go once the real cable lengths are in.

Check each segment separately, powered down, with an ohmmeter: 60 Ω across each segment on its own. Do the measurement with the extender's connector unplugged so you are measuring one segment, not both.

The extender itself is terminated only if it happens to sit at a physical end of that segment — the ordinary rule, applied twice.

Bus load

Every frame crosses. That means each segment carries its own traffic plus all of the other segment's, and the total the pair can carry is the total one 500 kbit/s MUXEN bus can carry. Splitting a bus in two with an extender buys you cable length and fault isolation; it buys you no extra bandwidth at all.

Plan the installation as one bus of the combined size. If the two halves together would overload a single bus, they will overload this one too — with the difference that the overflow is dropped quietly inside the box rather than showing up as bus errors. See Common mistakes — bus extender.

Addressing across the pair

The two segments are one MUXEN network, so the addressing rule of one MUXEN network applies to both at once: a function and instance pair appears exactly once across both segments.

A battery at instance 3 on segment A and a battery at instance 3 on segment B are the same collision as two of them on one wire — values that jump between sources, commands that reach the wrong device. It is an easy mistake to make when a segment is commissioned on its own, before the extender is fitted, from an instance list that only counts one half of the boat.

Keep one instance list for the whole boat. muxen-uds -i can0 scan run from either segment, with the extender running, lists every device on both.

What crosses and what does not

	Crosses
Ordinary MUXEN broadcast and command frames	yes, both directions
Requests for data (RTR frames) and their answers	yes
Configuration and firmware-update traffic for devices on the far segment	yes — a box on segment B is configured and updated from the Brain on segment A exactly as if it were local
Standard (11-bit) frames, and anything else on the wire	yes — the box repeats everything, it does not judge
Configuration traffic addressed to this box itself	no — it is answered on the segment it arrived on
Bus errors, bus-off state, electrical faults	no — each segment has its own interface, and this is the isolation you fitted the box for
The box's own life and startup frames	not "crossed": they are emitted on both segments, so the box is visible from either side

Nothing is filtered, delayed on purpose, or rewritten.

The box's own inputs and outputs

Two relays, two dry-contact inputs, two analog inputs, as on every CanCan, off by default and independent of the repeating function. See The hardware and Reference.