# CAN, RS-485 and Ethernet in the field

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

Page: https://dharanova.com/learn/field-buses · Track: Talk · Level: Core · Facts last checked 6 October 2026

Read first: [UART, I²C and SPI](https://dharanova.com/learn/uart-i2c-spi.md)

Diagram: Three rows. CAN (ISO 11898): three controllers share one differential pair, with built-in arbitration and error handling, and classical CAN runs at up to 1 Mbit/s; the largest payload is 8 bytes in classical CAN, 64 in CAN FD and 2048 in CAN XL (bars on a log scale; 2048 is 256 times 8). RS-485 (TIA/EIA-485): devices hang off one differential pair, up to 32 unit loads, with cable up to about 1,200 m at low data rates; Modbus RTU commonly runs over it. 10BASE-T1L (IEEE 802.3cg): a field device joins an Ethernet network at 10 Mbit/s over one twisted pair up to 1 km.

## 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. [1][2]
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. [3][4]
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. [5][6]
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. [7][8]

## Sources

1. [Classical CAN](https://www.can-cia.org/can-knowledge/can-cc), CAN in Automation
2. [CAN HS transmission](https://www.can-cia.org/can-knowledge/can-hs-transmission), CAN in Automation (CiA)
3. [CAN FD](https://www.can-cia.org/can-knowledge/can-fd-the-basic-idea), CAN in Automation
4. [CAN XL](https://www.can-cia.org/can-knowledge/can-xl), CAN in Automation
5. [The RS-485 Design Guide (SLLA272)](https://www.ti.com/lit/an/slla272d/slla272d.pdf), Texas Instruments
6. [MODBUS over Serial Line: Specification and Implementation Guide V1.02](https://www.modbus.org/file/secure/modbusoverserial.pdf), Modbus Organization
7. [IEEE 802.3cg-2019: 10 Mb/s single balanced pair Ethernet](https://standards.ieee.org/ieee/802.3cg/7308/), IEEE
8. [IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force: Objectives (approved 8 Mar 2018)](https://www.ieee802.org/3/cg/objectives_3cg_0318.pdf), IEEE 802.3