System Time

The system time is used as a reference when events such as faults or triggering of pyrotechnic actuators are recorded. This feature enables time recording of stored events in various control units.

The SIM is the bus master in the ISIS system and thus responsible for generating the synchronization pulses. This is why it makes sense for the SIM to also be the reference for the system time.

In the ISIS system, there is a uniform system time for all satellites (slaves). During production of the vehicle at the factory, the system time is started by means of a diagnosis command. This operation is only possible once, (a reset of the system time is not possible).

The resolution of this time is 250°s and it is triggered by the sync. pulses on the byteflight.  This means that only the actual operation time during which the byteflight  is active is recorded. The maximum time that can be recorded is over 76,000 hours.

The time is stored in the RAM of the microprocessor. Under the following conditions, there is also an entry in the EEPROM:

• Once per hour.
• On transition into the sleep mode.
• When the battery is disconnected (Shut-down signal from PM).
• When the complete system is supplied by the energy reserve.