Theory Of Operation
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The purpose of the diagnostic is to detect failures in any of the following microcontroller core functionalities:
Analog to Digital (A/D) converter.
- The A/D converter diagnostic is to ensure the rationality of the signals of both A/D converters in the TCM. The A/D converter monitoring is regularly commanding the A/D converter to convert different reference voltages from the TCM internal voltage regulator Application Specific Integrated Circuits (ASIC). The converted signals are compared to expected values.
Memory management.
- Detection of failures in the Random Access Memory (RAM) or Read Only Memory (ROM) and to check the functionality of the Error Checking and Correction (ECC) algorithm of the memory management unit.
Serial Peripheral Interface Bus (SPI).
- Detection of failures in the SPI communication between the Central Processing Unit (CPU) and the two safety relevant ASICs in the TCM by evaluating the feedback signal of sent SPI data, the control data that the receiving SPI node sends back to the SPI master and the status information of the low level SPI driver.
Failure of Output Coordinator Calculation.
- Detection of failures in the calculation of the output coordinator. The output coordinator software module controls the power stage commands from the upper level application software to the low level hardware routines. A safety function monitors the output coordinator by calculating the same commands using two independent algorithms.