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What is the compatibility test checksum ?
In EDC16/17 ECUs the memory is parted in blocks, which have different functions. These functions
are based on each other and so the blocks are depending on each other. The lowest level is the operating
system, above is the user program and at last the map data.
These blocks are connected over a data structure, which shall ensure that the blocks fit together.
So data areas can be erased and programmed without touching the rest of the memory contents.
If the user program is programmed, also the map areas must be programmed.
The name is this data structure is "compatibility test checksum". It will not be tested
in all ECUs, but for security reasons it should be calculated anyway.
In a few ECUs this implementation seems not to be correct, so that the modifications of these
values causes problems. Then it must be switched off.