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CAN, RS-485 and Ethernet in the field

Buses built for long cables and electrical noise, used in vehicles, factories and buildings.

Core

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CAN, RS-485 and single-pair Ethernet compared CAN is a differential bus shared by many controllers; its largest payload grows from 8 bytes in classical CAN to 64 in CAN FD and 2048 in CAN XL. RS-485 is a differential multi-drop link allowing 32 unit loads and about 1,200 m at low rates. 10BASE-T1L carries 10 Mbit/s over one twisted pair for up to 1 km. CAN ISO 11898 Differential bus shared by many controllers Built-in arbitration and error handling Classical: up to 1 Mbit/s Differential pair Controller Controller Controller Largest payload Log scale: 2048 is 256 × 8 Classical CAN 8 bytes CAN FD 64 bytes CAN XL 2048 bytes RS-485 TIA/EIA-485 Differential, multi-drop Modbus RTU commonly runs over it Up to 32 unit loads on one bus Device Device Device … Cable up to about 1,200 m at low data rates 10BASE-T1L Single-pair Ethernet IEEE 802.3cg Field device Ethernet network 10 Mbit/s one twisted pair up to 1 km Brings IP networking to field devices that once used serial buses
CAN and RS-485 are differential buses shared by many nodes; single-pair Ethernet brings IP networking to field devices over one twisted pair.

Key points

  1. Classical CAN (ISO 11898) is a differential, multi-controller bus with built-in arbitration and error handling, at up to 1 Mbit/s with payloads up to 8 bytes.12
  2. CAN FD raises the payload to 64 bytes and allows a faster bit rate during the data phase; CAN XL extends payloads to 2048 bytes.34
  3. RS-485 (TIA/EIA-485) is a differential physical layer for multi-drop links: the standard allows 32 unit loads on one bus and cable runs up to about 1,200 m at low data rates. Modbus RTU commonly runs over it.56
  4. Single-pair Ethernet such as 10BASE-T1L (IEEE 802.3cg) carries 10 Mbit/s over one twisted pair for up to 1 km, bringing IP networking to field devices that once used serial buses.78

Sources

  1. Classical CAN · CAN in Automation · Standard
  2. CAN HS transmission · CAN in Automation (CiA) · Standard
  3. CAN FD · CAN in Automation · Standard
  4. CAN XL · CAN in Automation · Standard
  5. The RS-485 Design Guide (SLLA272) · Texas Instruments · Reference
  6. MODBUS over Serial Line: Specification and Implementation Guide V1.02 · Modbus Organization · Standard
  7. IEEE 802.3cg-2019: 10 Mb/s single balanced pair Ethernet · IEEE · Standard
  8. IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force: Objectives (approved 8 Mar 2018) · IEEE 802.3 · Standard