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Immo Universal Decoding 3.2 Down

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I put together an Excel spreadsheet which can decode the 5AS data stream just to prove all of the above concepts and to allow me to work out the possible MEMS codes and EEPROM bytes for each of my immobilisers. I felt that the chances of making a mistake decoding them all by hand were too high, and even a 1-bit error could lead me down a blind alley. The spreadsheet allows you to enter any 72 consecutive bits of data from the data stream, not necessarily starting at the start of a message, and implements all of the logic above for decoding NRZ-S or NRZ-M, determining the odd and even bit streams, determining the offset to the start of the message and decoding the hexadecimal 16-bit data word transmitted and the corresponding EEPROM bytes. It also allows any of the unknown encoding options listed above to be selected.

This allows me to open a .BIN file dumped from an immobiliser EEPROM and manually edit the identified settings, or to load one .BIN file as a template and then load the settings from another and save the merged file. So, using the above utility I updated the .BIN file downloaded from one of the immobilisers and changed the MEMS code and EKA code to 5678 and the serial number to 5667788, and used the XPROG-M programmer to upload this back to the microcontroller to see whether it still worked properly, whether the transmitted data stream matched my encoding of the new MEMS code 5678 as expected and whether the ECU could then be matched to this new code.

Immo Universal Decoding 3.2 Down
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Using my software utility, I loaded the template .BIN file taken from the immobiliser whose behaviour I wanted to copy and updated it with the MEMS code, EKA code and serial number taken from the .BIN file downloaded from one of the other immobilisers, which was not showing the passive arming behaviour that I wanted.

If I rig up a programmable immobiliser test mule as discussed earlier it should bring the cycle time right down and allow me to tinker with these bytes and see what happens. I should be able to correlate some of the values with known behaviours from my existing downloads too. At least by programming the microcontroller directly I'm in no danger of bricking it by loading values that crash it; I can reload a known good set of data at any time, so I'm free to experiment. If I was talking to the assembled 5AS through a serial interface, anything I uploaded that it couldn't cope with might render it uncommunicative and leave me unable to put it back again.

In basic mode, it now acts as proper editor for setting the properties of an immobiliser. It lets you open one BIN file, downloaded from the microcontroller EEPROM, and update the various properties. The properties are defined using an external text file so additional properties can be added as found without recompiling the tool, unless they behave in some way not seen previously. Each property is edited in the appropriate format (e.g. binary, binary coded decimal, decimal or Boolean check box) and validated according to defined minimum and maximum values, allowed digits etc.
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Immo Universal Decoding 3.2 Down Aura Maire <maireaura72@gmail.com> - 2023-12-21 05:21 -0800

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