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Thread: 24 pin vs 28 pin chip.
04-03-2004 02:42 PM #1
24 pin vs 28 pin chip.
I have a 24 pin chip numbered 1267355206 that was in the glove box when I bought the car ('88 535is). I opened the ecu today and noticed a 28 pin Bav Auto chip installed. Is this 24 pin chip the stock one, and if it is, which slots does it go into. The first 24, or the last. The Motronic number on the box is 0261200059.
Also, anyone know if these BavAuto chips are any good.
04-03-2004 03:10 PM #2
Re: 24 pin vs 28 pin chip.
The car should only have one type of chip. If the 28pin chip is in there, and 4 of the pins arnt plugged in, the PO should have gotten the 24pin and didnt send back the chip. Try taking them both out and counting the pins to see which one should be in there. If the car is still running with that chip, my guess is that it isnt hurting anything. You can check the bavauto site for specs on their chips. They have one that can be re burnable to mods placed on the car for $350 and just their standard one that they dont reprogram for $250. I dont think they are quite as a agressive--i mean like more hp and torque gains-- as a conforti chip. I am still looking around for a chip for my car, but i need to get my brakes working first.
Hope this didnt just spit back the obvious you probably already knew.Andrew Elmore
1987 535is 5-speed
<img src="http://members.roadfly.com/ElmoreAndrew/sig.JPG" height=200 width=250>
04-03-2004 05:34 PM #3
Here\'s the 24 vs. 28 issue as I understand it...
All of the following is gleaned from the Internet. Use at your own risk- I haven't checked it out on my cars, nor do I intend to.
Some e28 535i MCUs have 24-pin (4 kbyte) chips and some have 28-pin (8 kbyte). The computer program that the MCU uses is divided up into two parts: code and data.
With the 24-pin variety, the code is resident in the the processor chip. This makes the processor a custom part, because it has to be programmed with the Motronic program. The data, on the other hand, is in the EPROM chip. That's the socketed part you can replace. This two-part approach probably made economic sense, because although a generic programless CPU would have been cheaper, the cost of the 28-pin EPROM necessary to store both the code and date would have have eaten up the savings.
Later on, as EPROM chips became cheaper, and 24-pin chips became harder to get (and more expensive), it was probably cheaper to go with the single-chip approach, putting both code and data into the 28-pin EPROM.
The 059 MCU was designed to allow either 24-pin or 28-pin chips. You have to add a couple of jumpers to the 24-pin variety, and a 28-pin socket, to use the 28-pin chip. My understanding is that the code is identical in either case, so you may only have to mess with one jumper. (The other jumper says, "run the code from the EPROM instead of whatever is in the CPU chip," so it doesn't matter how that jumper is set when converting from 24 pins to 28.)
The reverse may or may not be true. I don't know if the 28-pin variety has the code burned into the CPU chip. If it does, then you can go back to a 24-pin chip. Not sure if you have to mess with any jumpers.
04-03-2004 07:04 PM #4
04-03-2004 08:18 PM #5
04-03-2004 08:18 PM #6
04-03-2004 10:32 PM #7
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Not that you should do it, but pin 1 would be a
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04-03-2004 11:33 PM #8
Here's a link to the pinouts...
<a href="http://www.qsl.net/yo5ofh/data_sheets/mem-prom.htm">EPROM pinouts</a>.
The 24-pin type is the 2732, a 4 kbyte chip.
The 28-pin type is the 2764, an 8 kbyte chip.
It is apparent that the pins to leave empty when installing the 24-pin in a 28-pin socket are 1,2, 27, and 28.
These are the four pins closest to the "bite" taken out of the end of the chip. The socket will likely have a similar byte.
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