MOST Compliance and Quality Reliable Diagnostics of a MOST System

TTsuite is an efficient test system for the Electrical Control Line, developed by Ruetz System Solutions.
TTsuite is an efficient test system for the Electrical Control Line, developed by Ruetz System Solutions.

MOST is a proven standard of infotainment systems. A MOST network has high demands regarding performance and stability. Developers of these infotainment systems are aware that in case of a critical failure – ring break in a system where it cannot be diagnosed by the “switch to power” method via MOST, for example – there must be a powerful method for analyzing the network. ­Ruetz System Solutions, as part of the MOST Compliance Technical Group (MCTG), has developed an efficient test system for the Electrical Control Line. It ensures a constant high quality, so that in case of an error the diagnosis works correctly.

If failures are not found and not resolved quickly, the car is held up at the car workshop and that means the consumer loses confidence in the quality of the car as a product. To avoid this and fulfill important diagnostic purposes, the MOST Cooperation has introduced the Electrical Control Line (ECL) as a new optional feature for MOST150. ECL is the key element to increase diagnostic capability in a MOST system. It is the way to detect and allocate errors in the MOST system via an additional wire line. This wire line can also be used to generate an electrical wake-up signal.
The ECL protocol provides a variety of functions which can be divided into two separate groups:

  • Triggering a system test
  • Waking up the system by an electrical wake-up signal.

A device connected to the ECL can act in the role of an initiator and/or in the role of a participant. Because of the two separate functions there are two roles for each:

  • System test initiator triggers the test and collects the test results,
  • System test participant report the test results.
  • Electrical wake-up initiator creates the electrical wake-up signal,
  • Electrical wake-up participant is woken up by this signal.

There is exactly one system test initiator, but eventually more than one electrical wake-up initiator in a MOST system.
A system test message has three sequences: start sequence, parameter sequence and result sequence. Each message is initiated by the initiator and starts with the system test start impulse and optional retries, followed by the parameter sequence. The initiator generates five parameter values, which together define one of the four kinds of system test:

  • Ring break diagnosis (00000)
  • Alive (10000)
  • Coding error / threshold (01000)
  • Sudden signal off / critical unlock (11000)