Bosch laid the foundation for ISOBUS back in the 1970s, with the development of the CAN bus. They quickly discovered the fantastic possibilities that exist when ECUs can exchange data quickly and securely. In the meantime, many vehicles now have far more than fifty individual ECUs installed in them that communicate via CAN. We are now used to having our car radio lower the volume when we slow down. Hardly anyone thinks about how the radio actually knows how fast the car is going.
Why is there ISOBUS ?
For a long time, there were not so much electronics in agriculture and municipal service vehicles. A tractor was a tractor and electronics were not installed there. Too susceptible to faults. But soon the controls, which are now being used by all engine manufacturers and provide driving pleasure while at the same time ensuring environmentally friendly operation of the machine, also arrived here. The susceptibility to faults is now low and the tractors are running longer and more reliably than ever before.
Especially here in agriculture, the possibilities of networked ECUs are fantastic. Seeds and fertilizers are spread according to the characteristics of the soil. The complexity of the situation can be seen when a new seed drill is attached to the tractor and the appropriate control elements appear on the display in the driver’s cab. Data from the tractor, such as PTO shaft rpm and speed, are transmitted to the seed drill, from where control elements and indicators are transmitted to the tractor. Young farmers are not the only ones who enjoy this and the work is done quickly and with unbelievable precision and efficiency.
Since 2007, several companies have been working intensively together in the Competence-Center-ISOBUS to ensure that machines from different manufacturers are compatible with each other. The ISOBUS is now really taking off after the biggest hurdles have been overcome. Of course, the systems are still under construction, some manufacturers have misunderstood the standardization or are deliberately moving away from it. But this can no longer stop farmers, they are well on their way to digital agriculture and the journey is getting faster.
What is ISOBUS ?
The basis of ISOBUS is the CAN bus. If you want to measure in ISOBUS, all the basics that apply to the CAN bus are also valid. A two-wire line connects all control units, sensors as well as actuators. If one participant sends something, everyone else listens. It can happen that several participants want to send at the same time. Prioritization ensures that important messages can be sent first.
The CAN standard first establishes a physical basis for communication. One voltage level means a logical one, another a zero. Complex parameters have been described, e. g. bit timing. Clever framework conditions were created to enable robust communication.
The second level, described in the CAN standard, is the logical basis, which also provides for robust communication in a unique way. For example, participants can make non-understood messages invalid for the entire bus and thus trigger a repetition of the message.
Now we come to the third level, which regulates the protocol, i. e. determines how communication has to be done. This level was taken from the SAE J1939 standard, which had already established itself in powertrain, truck & trailer communication and construction machinery. Signals and parameter groups are used here, communication is effective, which enables low baud rates with fewer physical problems and longer cable lengths. Based on SAE J1939, the NMEA 2000 protocol was developed for marine applications, which defines specific parameters and signals. In defining ISOBUS, the best ingredients from all these worlds have been used and the basis for cross-manufacturer digital communication in agriculture has been laid. The unbelievable functions that can be realized with it are already visible in the manufacturers’ showrooms and at trade fairs. The end of the road is far from being reached.
The problems and how to measure them in ISOBUS ?
This brings a new field of responsibility to farmers and repair shops. Maintenance and repair of ISOBUS devices and systems. That’s not really easy. Of course, the manufacturers must deliver first. The systems must be properly designed and all electronics must be protected from influences. But the repair shop also has to be able to determine whether a bus is OK or not. This is a question that has caused extensive discussions in the automotive sector for decades. The forums of handymen are full of requests for help.
Digital communication has a special characteristic : it suddenly fails in the event of an error. Without warning, the DAB+ car radio suddenly becomes silent. In the analog FM car radio it became clear by increasing background noise that one moves out of the coverage area of a radio transmitter. Digital radio remains crystal clear until it fails. One or zero. When it’s running, it’s running – troubleshooting is impossible.
It is therefore difficult to judge whether a digital communication is fail-safe or not. Because even if it barely works, the content of the message is crystal clear. The breakdown is not announced by increasing noise. We have already described in this article why it is important to measure on the physical, analog level. Only there, in the analog environment, can I judge how good the signal quality on a digital bus is and whether there is still an amount of interference reserve or whether the communication is just barely possible.
If the brand-new tractor suddenly stops under the high-voltage line, but runs smoothly in the workshop and everywhere else, then the thought of a fundamental problem can come up. It is therefore also important for the manufacturer of ISOBUS systems and for the ISOBUS user to have a suitable measuring device in his hands in order to be able to evaluate the current quality of his bus.
With its CAN bus measuring and analysis devices, GEMAC provides the tools for evaluating the important physical basis of the bus. An engineer might now mention the oscilloscope as a measuring device. However, it is not only important to be able to measure at all, it is also important to be able to compare measurements. Here, the Quality Level provides a comprehensive informative value that is easily comparable. The unique generation of this value by 64x sampling of the bits allows repeatable and comparable statements. Since the physical basics are the same as in CAN, it is also possible to measure in ISOBUS.
Things like easy operability for non-electronic technicians and a simple measurement setup are not necessarily given with an oscilloscope. Although DSO’s become more and more intelligent when it comes to triggering an event, the evaluation of the oscillogram remains in the hands of the user. The CANtouch, on the other hand, allows every technician to operate and check the bus. The oscillogram can also be displayed for the expert.
PC software is also available for data receiving and decoding, decoding specific ISOBUS messages as well as standard J1939 messages and NMEA2000 specific content. Even manufacturer-specific PGN’s and SPN’s can be defined. This makes it possible to decode these special messages.