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Old Tue, Oct-30-2012, 02:55:16 PM   #137
BMW turbos with the factory ECU
Join Date: Jan 2004
Posts: 80
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Default Re: Comprehensive MSS54/MSS54HP DME Information

The ECU lockup due to too many flashes is not due to the EEPROM's characteristics. It's a 'feature' written into the boot code of the MSS52/54 ECU. This pseudo counter (which isn't really a counter) is different than the AIF counter present in other BMW ECUs. Actually, the AIF counter/limit is present in this ECU too. So you're still limited to 14 AIF writes (AIF counter), or about 60 writes in total (general reflashes). I've been able to come up with a way to reset the 'lockup' counter without desoldering the EEPROMs. It's helped tremendously with all the tuning required for a turbo kit.

Originally Posted by p0lar View Post
Here's a datasheet for the 29F400B EPROM chip. This isn't what's in the MSS54 DME, but it can replace the 28F400 that IS there. They operate similarly.

Note, on page 34, 'Erase/Program Cycles' => Min = 10,000, Typical = 100,000.


Also included is a datasheet for the Intel 28F400B3. I'm looking for an exact match still...

And, should you REALLY want to desolder the chip, you can use an adapter to a PSOP44 connector - there are less expensive ones, but these are known to work quite well. At that point, you use the Willem EPROM programmer and follow SOP.

The idea here, and what has been taken from industries vastly more advanced in nature, is to read the full contents of the OE DME (via JTAG or EPROM programmer (more difficult since it requires desoldering)), then flash using WinKFP or the Galletto 1260 and re-read the full contents of the EPROM again. Then note the differences, wash rinse and repeat and re-note differences again. After 2-3 flashes using standard tools, a specific counter should be easy to locate that is incrementing in serial fashion. It's quite plausible that this region can easily be rewritten even WITHOUT the use of the JTAG; either way, writing the original contents of the full flash prior to multiple flashing attempts will inevitably restore the counter to its original preset.
Nick Glantzis
Tuner of BMW Forced Induction ECUs
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