Information
CAN repeaters
Repeaters are used to establish a physical coupling of two or more segments of a CAN bus system. They can be used to implement tree or star topologies as well as for long drop lines. In addition, network segments can be electrically disconnected from each other because all repeaters are galvanically isolated.
A repeater works much like a line amplifier, amplifying the bits. This makes the operation transparent, ensuring the entire network reacts exactly as before. Repeaters can transmit bits not only electrically, but also via light through a fiber optic (FO) cable.
Advantages
The CAN channels coupled by the repeater are independent electric segments that can be optimally terminated in terms of signals. In this way topologies can be implemented that are not possible with a pure line of the bus due to electrical reflections.
According to the transceiver output capacities, the division of a CAN bus system into several subsystems, connected via CAN Bus Repeaters, increases the maximum number of bus nodes.
Another application of repeaters is the coupling of different physical CAN layers by means of high/low-speed repeaters, optical repeaters, or optical star couplers.
Bus-timing
As signaling is not directed in CAN, the repeater logic has to translate the signals of the segment received into the other and has to ensure that the input signals are not back-coupled. In terms of signals, the repeater corresponds to a line with relevant delay time. Therefore, it cannot be used to extend a CAN bus system.
Using repeaters does not influence the real-time behavior of a system because in terms of transmission behavior it corresponds to a network that consists only of lines.
Conventional bus structure
The example below shows a standard CAN bus structure, where all nodes should be connected to the same straight bus. Therefore, the CAN bus makes a U-turn to also connect the nodes in the middle.
The distance between the two nodes furthest apart (1/9) is 220 meters.
Extended bus structure
By connecting the middle nodes via a CAN repeater, the U-turn is no longer necessary. Note that the CAN repeater—due to the delay—virtually extends the subsection by 40 m.
The distance between the two nodes furthest apart (either 1/6 or 6/9) is 150 meters.
CAN hub repater
A CAN hub repeater is a typical variant that, in addition to the standard CAN bus connections, also has a CAN port on the rear, between the top headers of a DIN rail. This connection is designed to connect multiple CAN repeaters to a central hub via a backbone bus. It supports the creation of star and tree network topologies, extending the range of the CAN network and simplifying wiring.
A T-Bus connector is available for these repeaters, which fits into the DIN rail. This connector connects to the CAN port and can be interconnected simultaneously. This creates a backbone of multiple CAN repeaters.
