CAN Repeaters

Repeaters are used to establish the 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 long spur lines. In addition, network segments can be electrically decoupled using a galvanically isolated repeater.

The lines 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.

The division of a CAN system into several subsystems connected via CAN repeaters also allows the maximum number of bus subscribers defined by the transceiver output capacities to be increased.

As messages are not addressed in CAN, the repeater logic has to translate the signals of the segment received into the other signals in each case and ensure that the input signals are not back-coupled. In terms of signals, the repeater corresponds to a line with relevant delay time. It cannot therefore be used to extend a CAN 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 only consists of lines.

Another area of application of repeaters is the coupling of different physical CAN layers, e.g. by means of high/low-speed repeaters or optical repeaters.

The repeaters offered by IXXAT have an additional monitoring function. Connected network segments that are disturbed by permanent dominant levels, are detected and automatically disconnected, thus enabling the remaining network to continue functioning normally. After the fault has been eliminated, the operation of a disconnected segment is detected and the segment can automatically be reconnected to the network.

IXXAT also offers the repeater technology for licensed integration in customer hardware.

The CAN Repeater is used for the galvanic isolation of two segments of a CAN network, and for creating star or tree topologies. One special feature of the Repeater is that it can separate a defective segment from the rest of the network, so that the remaining network can continue working. After elimination of the defect, the segment is switched into the network again.

As an option, the Repeater can be equipped with a low-speed bus interface according to ISO/IS 11898-3. This allows operation of the Repeater as a high/low-speed converter. Its galvanic isolation isolates both CAN segments against each other as well as against the power supply.

The CAN-CR200 is used for the galvanic isolation of two segments of a CAN network and for creating star or tree topologies. Several CAN-CR200 can be connected to a CAN-hub via the integrated backbone bus. One special feature of the Repeater is the automatic recognition and separation of a defective segment from the rest of the network so that the remaining network can continue working. After elimination of the defect, the segment is switched into the network again.

The galvanic isolation isolates the CAN segments from each other as well as from the power supply.

The CAN-CR220 is used for the galvanic isolation of two segments of a CAN network and offers a very high galvanic isolation of 4 kV, allowing it be utilized in medical applications. One special feature of the Repeater is the automatic recognition and separation of a defective segment from the rest of the network so that the remaining network can continue working. After elimination of the defect, the segment is switched into the network again.

The galvanic isolation isolates the CAN segments from each other as well as from the power supply.

The CAN-CR220 is tested according DIN/EN 50178 (DIN VDE 0160: 1988-05 and DIN VDE 0160/A1: 1989-04).

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The CANbridge allows the coupling of two CAN networks, including networks with different bit rates. Unlike a CAN-Repeater, which only translates the electric signals, the CAN messages are received completely by the CANbridge and then sent to the other CAN network under consideration of filter and conversion rules (Store-Forward principle). With the aid of conversion rules (gateway tables), CAN messages can be filtered or forwarded under another identifier. With these mechanisms, the bus load can be reduced in the individual networks by only sending messages to the other network which are of interest.

The CANbridge has a powerful 16-bit microcontroller that can process bursts at higher data rates without message loss. LEDs show the current status of the coupled networks.

The CANbridge is configured via serial interface with a convenient Windows program. The configuration of the CAN-interfaces, setting of the operating modes and the filter- and conversion tables are saved on the bridge.

The CANbridge is available in three different versions: as an industrial version in a top hat rail housing or in a robust metal housing and as an automotive version in a robust metal housing.

Gateway mode
In the gateway mode the CAN@net II/Generic is connected to a PC or to a controller platform via TCP/IP. The application program on the host communicates via a standard TCP/IP socket and uses a simple ASCII protocol. The CAN@net II/Generic therefore provides simple, flexible access to CAN systems via a LAN or via the Internet.

Bridge mode
Using 2 CAN@net II/Generic, a CAN-Ethernet-CAN bridge can be implemented. This bridge enables the exchange of CAN messages between two CAN systems, where filter tables can be defined.

Configuration and firmware update
The configuration of the TCP/IP parameters can be performed using an easy to handle PC tool with automatic device detection. The configuration of the bridge functionality and the CAN communication is supported by an implemented webserver.

Bridge Mode
he bridge mode allows the user to set-up a CAN-Bluetooth-CAN bridge by using two CANblue/Generic devices. Message exchange occurs on layer 2 and is transparent. The CANblue/Generic can also be used in systems that work with CANopen, DeviceNet or customer-specific protocols. Filters for CAN identifiers can be stored in the devices for data exchange via Bluetooth. By using more than two CANblue/Generic devices the coupling of the devices can be made dynamically. The maximum distance between the CANblue/Generic devices is 100m, depending on environmental conditions.

ASCII Protocol Mode
In ASCII protocol mode, functions for transmitting and receiving CAN messages and for configuring the CANblue/Generic are available to the user based on simple ASCII commands. The CANblue/Generic is ideal for "non-Windows" systems or embedded platforms that will be connected wirelessly to CAN.

CANmodem is an intelligent gateway that allows remote access to CANopen systems via a conventional AT compatible modem.

The programming interface for Windows 2000/XP (API) provides functions for transmitting and receiving SDO messages as well as for configuration of the CANmodem. PC-based service and monitoring programs can simply access the CANmodem by means of the API via a telephone dial-up connection.

The CANmodem is a full CANopen node and has an object directory, two server SDOs and 127 client SDOs. Data of any length can be read and written via the client SDOs (segment size via Modem is 231 bytes). The module can act as a heartbeat producer and as a heartbeat consumer, can monitor up to 16 devices and transmit corresponding events in the CANopen network such as NMT events or heartbeat events. In addition, transmission and reception of any layer 2 messages is possible. This function can be used for transmitting and receiving any PDOs or for using the CANmodem with any CAN protocol.

In the event of service, many SDO accesses to the individual devices occur. The API not only allows SDO accesses to be initiated individually, but a whole list of SDO accesses, to be initiated, can be transmitted to the CANmodem. This list is then processed locally by the CANmodem and the result is then returned. With many SDO accesses, the propagation time via the telephone line plays a minor role.

The CANmodem can be connected to a conventional external AT-compatible modem via the full-duplex RS232 interface or directly to the PC. Communication occurs via a serial protocol based on the HDLC standard. For modem adaptation, a configurable init string can be saved in the object directory.

Connection between the PC and the CANmodem is made by means of a safe callback procedure. For this, the caller gives the CANmodem his callback number, which is checked by the CANmodem based on a white list. If the relevant number is entered in the white list, the modem calls the caller back and starts an authorization phase based on the CHAP protocol. After successful authorisation, the PC application can run all functions on the CANmodem.

With the CANlink II devices with a serial port can be connected to the CAN bus.

Two modes are available for use in CAN and CANopen networks.

In the CAN mode (layer 2) the received CAN data are transmitted transparently to the RS232 interface. Data sent by means of RS232 are packed in CAN telegrams and transmitted. One configurable identifier each is available for transmission and reception.

In the CANopen mode the CANlink works as a CANopen subscriber, where the serial data is saved as a bytestream object in the manufacturer-specific object dictionary range.

Supported CANopen features are:
- 1 server SDO expedited, non-expedited, no CRC check
- 1TX PDO static mapping
- 1 RX PDO static mapping
- Emergency message
- Heartbeat producer
- NMT slave

The communication interfaces and modes are configured with a configuration file which is saved on the device with an upload program.
The CANlink II is available in two housing versions, a plastic housing for top hat rail assembly or as a table-top device in a sturdy aluminum housing.