Safety Information Module (SIM)
Safety Information Module (SIM)
In the network of satellites, the Safety Information Module SIM is the central unit. The SIM has the following functions:
- Supply operating power to the satellites and provide an energy reserve in the event of failure of the voltage supply during an accident.
- The SIM is the connection master (using the Intelligent Star Coupler) and system master of the byteflight fiber-optic network.
- Triggering an automatic emergency call in the event of a collision.
The SIM is located behind the glovebox.
Power Supply of the SIM During Operation
The SIM is supplied with voltage KL terminals 30 and ground from KL31. If the vehicle voltage is sufficient then a switching controller (8) is supplied first, which supplies voltage to the intelligent Star Coupler (4) and the power supply (5).
The second switching controller (7) is supplied by KL 30 during operation and is controlled by the microprocessor via the cable SHDN 2. The capacitor is charged as of KL R.
The charging of the capacitor forms the emergency energy reserve. The capacitor voltage is 400 V.
Electrical Power Supply in the Event of a Crash
If the vehicle voltage falls below approx. 8 V, the switching controller (7) uses the reserve voltage from the capacitor.
The switching controller provides operating power to replace the missing voltage from KL 30 until the capacitor is fully discharged or the vehicle voltage is restored.
Operation of the switching controller is controlled by the microprocessor across the cable SHDN2. If KL R is off, the switching controller is switched off again, but there is no discharge of the memory backup capacitor.
Closed-Circuit Current Cutout
The switching controller (8), which supplies voltage to the Star Coupler and satellites, is switched off by the microprocessor (3) in sleep mode via the signal SHDN 1 (shut down) to reduce the current draw of the module to below 1mA.
In order to ensure the necessary basic functions occur also in sleep mode, a 9.8 V linear controller (1) is switched in parallel to the switching controller and this is permanently in operation.
The wakeable S/E (transmitter/receiver) modules in the Star Coupler and a downstream 5 V linear controller (2) are supplied with this voltage. This second linear controller supplies the microprocessor.
The satellites ( SZL, ZGM ) are connected to the wakeable S/E modules, and these satellites are able to wake up the byteflight. The other S/E modules are supplied via the switch (9) by the switching controller (8) and are switched off in sleep mode.
Intelligent Distributor
The intelligent distributor of the SIM performs the following tasks:
- Power supply for each individual satellite.
- Current limitation for each individual satellite.
- Power shutdown for each individual satellite in the event of a fault.
In order to ensure reliable function of the ISIS, all the satellites are supplied with voltage centrally by the SIM. To ensure that the system functions perfectly in the event of a short circuit or overload on one of the supply lines, there must be an intelligent current distribution.
The distributor integrated in the SIM limits the current on each supply line to the satellites to 100 mA (Approx.10V). An exception is the SZL, which has a current intake of approx.120 mA, as the steering wheel electronics are also supplied.
If this current limit is exceeded, it causes a reduction in the current output. It is also possible to switch off each individual satellite.
Intelligent Star Coupler
The transmitter and receiver module is a component that is able to convert electrical signals into optical signals and transmit them across the byteflight fiber-optic bus.
Each satellite has a transmitter and receiver module (S/E module).
Each of the S/E modules is connected via the byteflight with the Intelligent Star Coupler in the SIM. In the SIM, there is also a transmitter and receiver module for each satellite.
byteflight Master
The byteflight master has two tasks to perform:
- Generation of the synchronization pulses (Sync. Pulse)
- Setting the satellites in alarm mode (Alarm Pulse)
In the ISIS,the SIM is configured as byteflight master (bus master). In principle, any satellite can be configured by software as bus master. However, there may only be one bus master in the system.
All other satellites (bus slaves) use the sync pulse for internal synchronization. Each slave can transmit telegrams between the sync. pulses on the byteflight.
Synchronization Pulses
The SIM provides the synchronization pulses at intervals of 250 micro seconds. The alarm mode is transmitted across the width of the sync. pulse.The duration of a sync. pulse in alarm status is approx.2 micro seconds. Normally, the synchronization pulse lasts approx.3 micro seconds.
The duration of a complete telegram can vary between 4.6 to 16 micro seconds.
On the basis of all the available information provided by the sensors, the bus master (SIM) must decide whether the satellites are to be set in the alarm mode.
When the alarm mode is set by the SIM, all the trigger circuits (B+) of the ISIS are placed on trigger standby.
To trigger a stage, two separate signals must always be transmitted on the byteflight.The high-side (B+) switch of the trigger circuit in the satellites is controlled via the alarm mode of the byteflight.
The low-side switch is controlled by the microprocessor in the satellites. On the basis of the transmitted telegrams with the sensor signals, the trigger algorithm recognizes when the low-side (ground) switch has to be closed.
The following graphic uses a trigger stage as an example to show signal paths necessary for triggering.
Watchdog Function
The Intelligent Distributor allows the SIM to deactivate the power supply for individual satellites. This possibility is used to implement a watchdog function. The relevant status telegram is used to monitor the satellites. If any of the following faults is detected by the bus master (SIM), the satellite is deactivated:
- Internal fault in the satellite.
- System time incorrect.
- Status telegram not received.
Depending on the type of fault, up to two attempts are made to switch on again after 100 ms. If the power on reset in the satellite module does not rectify the fault, the satellite remains off until the next wake-up of the bus system.
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 micro seconds 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.
Synchronization of the System Time
In order to ensure the same system time in all modules, a regular synchronization of all satellites is necessary.
There is a distinction between the synchronization in normal operation and synchronization of new modules installed in the vehicle as spare parts.
The mileage reading is also stored in the SIM. In order to set up a relation between the system time and mileage reading, the current mileage reading is saved during the synchronization of the system time.
Synchronization in Normal Operation
When the byteflight is started following sleep mode and approx. every 16s during operation, the SIM transmits a "system time" telegram.
Due to the relatively low priority of the telegram, there is no assurance that the routing takes place immediately. This leads to a possible difference between the time in the SIM and the time in the satellites.
As the SIM knows the time of the transmission of the telegram, a correction is possible.
A second telegram "system time" with the correction value as part of the content is sent.
The correct system time is therefore the total of the values of the two system time telegrams. The satellites only adopt the system time when both system time telegrams have been received.
Self-Diagnosis of the ISIS
The self-diagnosis of the overall system ISIS consists of:
- Self-diagnosis of the SIM
- Pre-drive check, phase 1
- Pre-drive check, phase 2
- Self-diagnosis in operation
Self-Diagnosis of the SIM
When KL R is switched on, or at wake-up, an internal self-diagnosis of the SIM is carried out first.
If a fault occurs during the tests, it is entered in the fault memory, stopping the program and disabling communication on the bus.
Since the instrument cluster receives no bus signals, the airbag warning lamp (AWL) is activated.
Pre-Drive Check
When KL R is switched on, a self-diagnosis of the overall systems is carried out. During this period the system cannot be triggered.
This is indicated by activation of the airbag warning lamp AWL. The total duration of a fault free pre-drive check is less than five seconds.
The pre-drive check is divided into two phases.
The pre-drive check only starts when the SIM has received the first control unit status messages from all of the satellites known by coding and no fault has been communicated.
If the status message of a module is not received or if a fault has been communicated, the power supply of the satellite module is switched off.
Pre-Drive Check, Phase 1
In phase 1 of the pre-drive check, the igniter output stages are tested (with the exception of the high-side transistor, which is controlled via the alarm pulse).
During phase 1, no alarm pulse is generated. The sensors are stimulated and tested. On conclusion of this test the result is communicated in the control unit status telegram. An OK signal is only transmitted if all the tests have run without faults.
If any faults occur during the pre-drive check, these are stored in the fault memory,
Pre-Drive Check, Phase 2
In phase 2 of the pre-drive check, the alarm path from the SIM to the igniter output stages is checked.
The SIM transmits an alarm pulse, which is taken back after a 30 ms waiting period. Now each satellite transmits a status telegram with an OK signal to the SIM.
If the alarm mode is not correctly received, a fault entry is made in the fault memory.
This concludes the pre-drive check and the modules can now start normal operation. This means that the satellites with ignition capacitors can now be charged.
If all ignition capacitors are fully charged, this is notified in the status telegram to the SIM.
The AWL is switched off when all the modules report full ignition capacitors and no fault is stored.
Self-Diagnosis During Operation
During operation, the SIM continuously monitors itself. If a fault is found, the byteflight communication is stopped and the power supply of the satellites is switched off by the SIM.(See watchdog function)
The S/E modules are capable of diagnosing the optical signal quality. A warning signal is generated when the optical reception quality falls below a certain threshold. The communication still can function without faults.
The SIM and all the satellites continuously check the VIN received across the byteflight against the VIN entered in the control units. If there is no match or an entry is missing, the AWL is switched on.