Bus extender (010010032) — Overview

This firmware does not translate anything. It takes two MUXEN bus segments and makes them behave as one bus.

Every frame the box hears on one connector, it puts out on the other. Every frame. In both directions. No filtering, no selection, no address list to maintain. A device on the far segment is seen by the Brain exactly as if it were wired to the same pair of wires, and a command sent from a screen reaches it the same way.

The box is a repeater, not a router. It has no idea what the frames mean and never edits one: identifier, data, length and the request-for-data flag come out on the far side exactly as they went in. It is the wire that changed, not the message.

Why you would fit one

• A cable run that is too long, or split by a bulkhead. Two shorter, properly terminated segments carry better than one long one.
• A part of the boat wired separately — a flybridge, an engine room, a hull half on a catamaran — that has to join the main bus without pulling a new trunk cable through the boat.
• Keeping a faulty section from taking the whole bus down. Each segment has its own bus interface. A short or a jammed transmitter on one side stops traffic from that side; it does not put the other segment into fault.

What it means for the boat

Because the two segments become one logical bus, everything that is true of one MUXEN bus is now true of the pair:

• Addresses are shared. A function and instance number used on one segment cannot be reused on the other. There is no "segment 2 namespace" — see Wiring, termination and load.
• Bus load adds up. Each segment carries its own traffic plus all of the other's. Two half-loaded segments make one full bus.
• Termination does not. They stay two electrically separate segments, and each one needs its own two 120 Ω terminations — four in total, not two. This is the mistake that gets made.

What it is not

• It is not a speed converter. Both sides run at 500 kbit/s, fixed. It cannot join a MUXEN bus to an NMEA 2000, J1939 or any other network — those have their own CanCan applications.
• It is not a filter or a gateway. Nothing is dropped, nothing is renamed, nothing is rate-limited. If a segment is noisy, the noise crosses too.
• It is not a bus repair. It makes two good segments into one bus; it does not rescue one bad one.
• Only one extender may sit between the same two segments, and the segments must never form a ring. There is nothing in the box that detects a loop, and a loop makes a frame circulate for ever.

Identity

	v1	v2
Product ID	010010032	010010032
Hardware	CanCan v1 (990010047)	CanCan v2 (990010061)
Software ID	990050023	990050023
Version	5.1	6.2
Image	010010032-app_bus_extender-firmware.srec	010010032-V2-app_bus_extender-firmware.srec

Limits

Speed, both segments	500 kbit/s
Frames buffered per direction	64
Segments joined by one box	2

Read next

• Wiring, termination and load — wiring, termination, load, addressing
• Commissioning — commissioning, in the right order
• Common mistakes — bus extender — what usually goes wrong
• Reference — bus extender — parameters, devices, what crosses
• CanCan gateways — what is true of every CanCan gateway