The microprocessor (µP) used in the ML1.1 &  ML1.2 designs was replaced by a microcontroller (µC) in the ML3.1 design. The 8051 µC is a single chip microcontroller developed by Intel in 1980. The 8051 µC has CPU, RAM, ROM, I/O, interrupt logic, and timers all in a single chip. The internal ROM has preprogrammed operating code and data. The internal ROM size is 4K x 8. The total ROM size was doubled with an external 2732 EPROM. 

In 1987, BOSCH made production changes in the ML3.1 design. This redesign appeared late in the 1987 production year of the Porsche 944. The 24 pin socket and 2732 EPROM were replaced with a 28 pin socket and 2764 EPROM. The internal ROM of the 8051 µC was no longer used. This had the advantage that the first half of the operating code could now be corrected or improved.