connector or cable wiring scheme
9 pin D-SUB male connector
| Pin | Name | Description |
|---|---|---|
| 1 | Reserved | Upgrade Path |
| 2 | CAN_L | Dominant Low |
| 3 | CAN_GND | Ground |
| 4 | Reserved | Upgrade Path |
| 5 | CAN_SHLD | Shield, Optional |
| 6 | GND | Ground, Optional |
| 7 | CAN_H | Dominant High |
| 8 | Reserved | Upgrade Path |
| 9 | CAN_V+ | Power, Optional |
Controller Area Network (CAN) is a broadcast, differential serial bus standard originally developed in the 1980s by Robert Bosch GmbH for connecting electronic control units (ECUs). The physical and data-link layers are standardised in ISO 11898, which defines the differential balanced-pair signalling used by both the CiA (CAN in Automation) 9-pin D-SUB connector shown above and the SAE J1939 heavy-duty vehicle network — two distinct upper-layer protocols that share the same underlying bus. The CiA 9-pin D-SUB arrangement is widely used in industrial and embedded control applications, while SAE J1939 targets trucks, buses, and construction equipment and specifies its own Deutsch HD10-9-1939 round connector (J1939/13). Bit rates up to 1 Mbit/s are achievable at network lengths below 40 m; reducing the bit rate permits longer distances (for example 125 kbit/s at 500 m), while J1939 standardises 250 kbit/s with newer networks supporting 500 kbit/s.
Notes
- The bus uses differential signalling: CAN_H idles at 2.5 V (recessive) and rises to approximately 3.5 V dominant; CAN_L idles at 2.5 V and falls to approximately 1.5 V dominant.
- Both ends of the bus segment require 120 Ω termination resistors between CAN_H and CAN_L; the combined parallel resistance of ~60 Ω is measurable across the bus when unpowered.
- CAN_SHLD (pin 5) and GND (pin 6) are optional in the CiA connector layout; their use is recommended for noise immunity in industrial environments.
- Reserved pins (1, 4, 8) are designated upgrade paths and must not be connected.
- J1939 and CANopen/CiA are distinct upper-layer protocols: J1939 (SAE, heavy vehicles) uses CAN 2.0B with 29-bit extended identifiers; CANopen (CiA, industrial) commonly uses 11-bit identifiers. Both run on the ISO 11898 physical layer.
Signals
- CAN_H — CAN bus high signal line (dominant high); differential pair with CAN_L
- CAN_L — CAN bus low signal line (dominant low); differential pair with CAN_H
- CAN_GND — CAN bus ground reference
- CAN_SHLD — Cable shield connection, optional; typically connected to chassis ground at one end only to avoid ground loops
- GND — Additional ground, optional
- CAN_V+ — Optional bus power supply line; not present in all implementations
- Reserved — Pins 1, 4, and 8 are reserved for future use and must remain unconnected
References
- SAE J1939/13 Off-Board Diagnostic Connector — SAE International, October 2016
- J1939 Explained – A Simple Intro (2026) — CSS Electronics
- SAE J1939 Network Wiring and Connectors — JCOM1939 Monitor Pro (Copperhill Technologies)