Control devices via CI and CAN bus on the PCU

The PCU is not just a display, but also a control panel. Refrigerator, heating, air conditioning and other onboard technology can be operated directly on the display via CI and CAN bus. This replaces a number of individual control panels — but it requires the devices to have a bus interface in the first place.

What a bus changes

Traditionally, each device has its own control panel and its own cable to it. Four devices mean four panels on the wall and four cable runs. The bus reverses this: All devices are connected to a common line and exchange messages on it. One control unit is sufficient because it can communicate with every participant.

The second difference is more important: Not only does the command flow via a bus, but also the feedback flows back. A classic switch does not know if the device is running - it only knows its own position. A bus participant reports its actual status. Therefore, the display can show that the heating is on and what temperature it should run at.

CI Bus and CAN Bus

Both interfaces are integrated into the PCU; additional modules are not necessary. They fulfill different tasks.

The CI Bus is common in vehicle construction and connects body components – heating, refrigerator, air conditioning – with each other. It is precisely tailored to this class of devices.

The CAN Bus is the more general technology underneath. Many protocols are based on it, both in the vehicle and marine sectors. Therefore, the decisive factor is not whether a device "can CAN," but which protocol it speaks. Two devices on the same CAN cable that speak different protocols will not understand each other - even if the plug connection fits.

WarningA suitable plug does not guarantee compatibility. Before purchasing a device that is to be operated via the PCU, it must be checked which interface and which protocol it actually supports.

Laying the bus cable

A bus is a line, not a star. The cable runs from one end to the other, and the participants are connected via spur lines that are as short as possible. If, instead, a separate long cable is laid from a central point to each device, reflections are introduced, which appear as sporadic dropouts — i.e., as the most difficult error to find.

There should be a terminator at both ends of the line. If it is missing, the bus often still runs, but unreliably: short distances are forgiving, long ones are not. The error then appears as a device that "sometimes" does not respond.

The bus line must be kept separate from the power section. If it is run parallel and close to an inverter supply line, the inverter's switching operations will couple in.

Setting up devices

The logical order for commissioning:

1. Connect one device at a time. Connecting all of them simultaneously and then searching for why one is missing takes many times longer.
2. After each device, check if it appears on the display and if it responds to a command.
3. Name meaningfully. "Living room heating" will be understandable in two years, "Device 3" will not.
4. Determine the order on the display — by frequency of use, not by connection order.
5. Check limits. What the display shows is not always everything the device can do; some functions remain on the device itself.

Where the limits lie

A bus controls devices that have a bus interface. Everything else – the reading lamp, the water pump, the fan – remains a classic circuit. For these consumers, a switching module that actually switches and secures the circuit is the way to go, not the bus connection.

Keeping this separation clean simplifies planning: bus devices are operated via the bus, and circuits are switched via the distribution or a switching module. The PCU can combine both on one interface – but the underlying technology remains different.

Typical errors

• Wired as a star instead of a line. Manifests as sporadic dropouts, not as a clear failure.
• Terminator forgotten. The bus tolerates this over short distances — until the system grows.
• Inferred compatibility from the connector. The protocol is decisive, not the plug connection.
• All devices connected simultaneously. Makes any troubleshooting a search for a needle in a haystack.
• Expecting classic consumers via the bus. A lamp without a bus interface needs a switching module, not an address.