Physical medium attachment

The basis for transmitting CAN messages and for competing for bus access is the ability to represent a dominant and a recessive bit. This is possible for electrical, optical, and further media. For electrical transmission media, types of physical medium attachments are specified in ISO 11898-2/-3/-5/-6, ISO 11992 and SAE J2411. For other transmission media, only manufacturer-specific solutions exist.

ISO 11898-2 High-speed transceiver

The high-speed transceiver is the CAN transceiver that is used most often in CAN-based applications. The high-speed transceiver supports a transmission rate up to 1 Mbit/s in networks reaching up to 40 m. The high-speed transceiver supports a bus-line architecture and transmits a differential voltage via a CAN-High and a CAN-Low line. The bus line is terminated by means of 120-Ohm resistors at both ends of the line. Typically, high-speed CAN transceivers can drive up to ca. 110 network participants.

ISO 11898-3 Fault tolerant transceiver

Currently, the fault tolerant transceiver is only used in the car body electronic and some further niche markets. Networks based on this transceiver can integrate up to 32 devices at a transmission speed of up to 125 kbit/s. Although different voltage levels are used compared to the ISO 11898-2 transceiver, the fault tolerant transceiver drives a differential voltage as well. But in contrast to the high-speed transceiver, the fault tolerant transceiver is capable of detecting failures on the physical layer level and is able to switch to a single wire transmission. In addition, the fault tolerant transceiver supports a low power mode. As the applications fields of this transceiver are declining, the long-term availability of this transceiver is endangered.

ISO 11898-5 High-speed transceiver with low power mode

The high-speed transceiver with low-power mode is a further development of the ISO11898-2 transceiver. In addition to the ISO 11898-2 transceiver this transceiver type supports a low power mode. For power saving purposes, devices attached to the CAN via this transceiver, can be set into a sleep mode and even the power consumption of the transceiver itself is reduced. The transceiver is well suited to switch on and off power-saving/sleep mode in entire networks, e.g. in battery-buffered applications. A selective sleep mode handling for individual network participants is not supported.

ISO 11898-6 High-speed transceiver with selective wake-up capability

The high-speed transceiver with a selective wake-up capability is a comprehensive further development of the ISO 11898-5 transceiver. In addition to the ISO 11898-5 transceiver, this transceiver type supports an individual wake-up/sleep handling. Therefore, a certain degree of CAN controller capability is implemented in the CAN transceiver as well. In addition to a frame compare logic, this allows configuring specific wake-up frames in all network participants.

SAE J2411 Single wire transceiver

The single-wire transceiver according to SAE J2411 is intended for CAN-based applications with low requirements regarding bit-rate and bus length. The communication is based on one bus line with a nominal data rate of 33,3 kbit/s (83,3 kbit/s in high-speed mode for diagnostics). The main application area of this transceiver is in automotive comfort electronic applications. In those applications, an unshielded single wire connects up to 32 network participants. A linear bus topology is not necessary. Selective sleep-mode capability is supported.

ISO 11992 Point-to-point

The ISO 11992 standard defines a point-to-point connection for use in e.g. towing vehicles and their trailers. For one vehicle with one trailer, a point-to-point connection is defined. For one vehicle with two trailers, a daisy-chain connection is defined. The nominal data rate is 125 kbit/s with a maximum bus line length of 40 m. The standard defines the bus error management and the supply voltage (12 V or 24 V). An unshielded twisted pair of wires is defined as the bus medium.

Optical transmission

The fiber-optical transmissions of CAN signals is not internationally standardized. Due to the directed coupling into the optical media, the transmitting and receiving lines are provided separately. Also, each receiving line is externally coupled with each transmitting line in order to ensure bit monitoring. A star coupler can implement this. The use of a passive star coupler is possible with a small number of nodes, thus this kind of network is limited in size. The extension of a CAN network with optical media is limited by the light power, the power attenuation along the line, and the star coupler rather than the signal propagation like in electrical lines.

Advantages of optical media are an emission- and immission-free transmission and complete galvanic decoupling. The electrically neutral behavior is important for applications in explosive or electromagnetically disturbed environments.