1982/1984 version of the ML1.2

The early Motronic ML1.2 had four ROM chips soldered into the board. Each ROM contained 1k X 8 of memory for a total of 4k X 8. Each 8-bit word contains one piece of data or one computer instruction. The early Motronic was limited to 4,096 lines of computer instructions and data.

Whether it is for a Porsche or for a BMW, the first two ROMs will have the same part numbers. Subroutine libraries and data are located in the first two ROMs.  Any data and programming specifically for a particular model will be found in the second two ROMs. Programming that is not specific to any particular model is include in the first two ROMs. It is cheaper for BOSCH to buy large numbers of the same part. In electronics, the larger the quantity of parts you buy, the lower the price per part becomes.

These are mask programmable ROMs. They are programmed during manufacturing. Ordering ROMs can be a lengthy process. Lead times can be as high as 6 months of longer (from parts order to parts received). A copy of the code is sent to the manufacturer (RCA Semiconductor). The ROM artwork is created and a trial run of ROM prototypes is made. These prototypes are sent to BOSCH for approval. Once the ROMs are checked and the code is verified, production begins. The actual programming of the ROM is done with special artwork for internal layers of the ROM. This is costly in small numbers but is very reasonably priced when buying large quantities like BOSCH has. It has the disadvantage of having large numbers of parts that have to be scrapped when a programming error or update is made. Production lines have been stopped waiting for custom microcircuits to arrive.

What about EPROMs? The are programmed in house or sent out to be programmed. Each EPROM takes about 2 minutes to program. What happens if there was a code change that would stop the production line if it used ROMs? A technician takes the updated code and blank EPROMs to his programmer in the morning. In the afternoon, the EPROMs are in kits. By late afternoon, they are being soldered into PCBs (printed circuit boards). Big difference? The lead time problem goes away. The disadvantage was that in the mid 1980's, EPROMs were very expensive. Prices eventually came down. EPROM life was not expected beyond 10 years.

1985.0 version of the ML1.2

The 4 ROMs were replaced by a single 4k x 8 EPROM. BOSCH made this change and a few made it into 1985.0 year 944s. Very few were made and Porsche changed DMEs to the ML3.1 in mid year 1985. This was the first appearance of the EPROM in a Porsche Motronic DME and the beginning of the aftermarket performance chip industry.

1985.5/1987 version of the ML3.1

The late Motronic ML3.1 had a single 4k x 8 EPROM that fit into a 24-pin socket. The CPU was changed to an Intel 8051 Microcontroller which contains an additional 4K x 8 of ROM. The total memory has doubled in size since the ML1.2 to 8k x 8. And like the ML1.2, all basic subroutine libraries and data are stored in the internal 8051 memory. There is just a single BOSCH part number for all the 8051s chip used in ML3.1 whether it is found in a 944, a 911, or a BMW. All the programming and maps specifically for the 944 is found in the EPROM. Over the years that the ML3.1 was used in the 944, the EPROM was changed 5 or more times.

1988/1989 version of the ML3.1

The Change was made by BOSCH in late 1987 but is referred to as the 88 redesign. There is much confusion about the 1988 DME and much of it is nonsense. The memory size is the same as the 86 DME. In 1988, the 4k x 8 EPROM was replaced by a 8k x 8 EPROM. The 24-pin socket was replaced with a 28-pin socket. The final change was to add a jumper to the board that instructed the 8051 to ignore its internal 4k x 8 memory. All 8k x 8 of memory is now stored in the EPROM.