Physical-layer options

The CAN PMA (physical medium attachment) sub-layer is typically implemented in CAN transceiver chips as standardized in ISO 11898-2

There are standardized several CAN PMA (physical media attachment) sub-layers. They are typically implemented in transceiver chips. Most common is the CAN HS (high-speed) transceiver. This includes variants supporting bit rates up to 1 Mbit/s.

So-called CAN FD transceivers with tighter symmetry features are suitable for bit rates higher than 1 Mbit/s and can be used in CAN FD networks using in the data-phase bit rates of 2 Mbit/s and more.

The CAN SIC (signal improvement capability) transceivers are able to suppress ringing on the network lines. They are standardized in ISO 11898-2:2024. The CAN SIC XL transceivers (also standardized in ISO 11898-2:2024) support two modes: SIC mode and FAST mode. In FAST mode, they use a PWM (pulse-width modulation) coding instead of the NRZ (non-return-to-zero) coding used in all other CAN transceivers. In FAST mode, you can achieve bit rates of up 20 Mbit/s depending on your physical network design. Using CAN SIC or CAN SIC XL transceiver may limit the arbitration phase speed to 667 kbit/s, when applying all CAN identifier values.

Most of the CAN physical-layer options use twisted-pair copper cables with common ground usually realizing the physical transmission. Of course, all connected nodes need to support the same bit rates. Note that sample-point setting variations in the connected nodes leads to restrictions in the speed/length ration.

To summarize, there are the following PMA options:

  • CAN HS transceiver with optional low-power and optional selective wake-up capability (first standardized in ISO 11898-2:2016)
  • CAN FD transceivers with optional low-power and optional selective wake-up capability (first standardized in ISO 11898-2:2016)
  • CAN SIC transceiver with optional low-power mode and optional selective wake-up capability (ISO 11898-2:2024); these options limit the data-phase speed to 5 Mbit/s
  • CAN XL SIC transceiver (ISO 11898-2:2024) with SIC mode and FAST mode (bit rates of up to 20 Mbit/s achievable)
  • CAN low-power/fault-tolerant transceiver (ISO 11898-3:2006) with a maximum bit rate of 125 kbit/s – no longer recommended for new designs
  • CAN truck/trailer transceiver (ISO 11992-1) with a bit rate of 125 kbit/s – required by European regulations
  • Single-wire CAN (SWC) transceiver (SAE J2411) – no longer recommended for new designs

Medias others than copper cables are also in use: fiber-optic and power-line transmissions, for example. However, their specifications are proprietary.