Battery voltage is at 12 Volts. If the battery voltage drops to 0 Volts in 5 us and stays at 0 V for 100 us, then rises back to 12V in 5 us, what impact will this have on Microcontroller memories, different microcontrollers inputs like Analog, Digital, PWM, etc. And different outputs like Digital, PWM etc.
Will the contents of I/O and memories like SRAM, Program Flash, Data Flash change due to this transient?
The microcontroller on the ECU is Infineon Aurix TX29x.
Correction! The Microcontroller is Infineon Aurix Tricore TC29x
That depends on the board. A well-designed automotive board should be able to survive glitches like that, but I couldn't tell you exactly what duration of glitch would normally be fatal and which wouldn't.
If the microprocessor and memories themselves suffered such a glitch in their power supply rails, then the processor would probably reset, and in most cases the flash (unless it's being written to) would probably be OK. The contents of the RAM wouldn't matter, because the processor would be starting over again.
There should be a SAE standard governing such things -- it may help to google around for "automotive power interruptions" or "automotive power interruption standards".
The voltage drop was already explained by Tim and Ians, that can be also simulated with a simple setup(power MOSfet driven with the pulse), depending on your board the effect will vary from none to catastrophic :)
The other major effect, not mentioned until now is the strong ElectroMagneticPuls (EMP) generated by a big swing on the battery voltage. This happens during cranking, (during starting the engine) then you have the biggest load on the battery, and that massive few hundred Amps of current will generate a strong electro-magnetic field, this will couple trough the wires and it will affect at least the sensitive ADC circuits.