History
ISOBUS grew out of Germany’s LBS agricultural bus (DIN 9684), standardised from 1991, and SAE J1939, on which it builds its 250 kbit/s CAN layers. It was first shown at Agritechnica in 2001, and ISO 11783 was published in parts from 2002 onward; Part 2, the physical layer with the hitch connector, appeared in 2002, with new editions in 2012 and 2019. The 2019 edition added a twisted-pair physical layer (TPPL) based on SAE J1939-15, which uses plain 120 Ω termination and works with older machines in both directions.
In 2008 the manufacturers founded the Agricultural Industry Electronics Foundation (AEF), which tests and certifies ISOBUS by functionality — Universal Terminal (UT), Task Controller (TC-BAS, TC-GEO, TC-SC section control), auxiliary controls (AUX-N), Tractor ECU (TECU) and Tractor Implement Management (TIM). Two machines work together only on the functionalities both support. AEF’s “High Speed ISOBUS” is a separate Ethernet network, not a faster CAN.
Where you will find it
- Running any certified implement from one universal terminal
- GPS section control and variable-rate application
- Documentation and implement monitoring
- Joystick and auxiliary controls (AUX-N)
- Telematics and data loggers reading the bus through the in-cab or diagnostic connector
Why ISOBUS has terminator pins
A plain CAN bus is terminated by a 120 Ω resistor at each end. ISOBUS instead uses terminating bias circuits (TBC) that sit outside the ECUs and are powered over their own pair, TBC_PWR and TBC_RTN, so the bus stays correctly terminated whenever an implement or ECU is unplugged. The tractor’s hitch socket contains a TBC. Inside the implement plug, pin 4 (ECU_PWR) is bridged to pin 5 (TBC_DIS): when the plug goes in, the socket switches its own terminator out, and the termination moves to the far end of the implement’s bus. Unplug the implement and the socket reconnects its terminator automatically.
Makers colour-code the sockets: black inserts are active (they power the terminators; one per tractor network) and grey are passive, used at the front of the tractor or on pass-through implements.
In-cab connector
Terminals, joysticks and other in-cab devices join the bus through a 9-pin TE CPC connector in the cab, descended from the LBS socket. The bus loops through it, so CAN High and CAN Low each have an in and an out pin:
| Pin | Signal | Pin | Signal |
|---|
| 1 | Not used for signals | 6 | TBC_PWR |
| 2 | CAN Low in | 7 | ECU_PWR |
| 3 | CAN Low out | 8 | TBC_RTN |
| 4 | CAN High in | 9 | ECU_GND |
| 5 | CAN High out | | |
Terminator plug
Where a bus ends away from a socket, an in-line 6-pin terminator plug carries the TBC: A ECU_PWR, B TBC_PWR, C ECU_GND, D TBC_RTN, E CAN High, F CAN Low.
Diagnostic connector
ISOBUS machines use the same 9-pin Deutsch diagnostic connector as J1939 trucks. The tractor’s own J1939 bus stays on pins C and D; on ISOBUS tractors the implement bus is on pins H and J. Choose the “ISOBUS tractor” pin-out on the 9-pin page to see it.
