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Replacement memory cartridge for the MK-90 microcomputer


The circuit was built with a small microcontroller and serial FRAM nonvolatile memories.
The FRAM chips cannot be replaced with EEPROMs.
The series resistors on the bus and the diode (preferable Shottky) are for protection purpose only, and could be omitted.

circuit diagram of the replacement cartridge

photo of the replacement cartridge


download - AVR source code

The "Read Postdecrement" function (not used by the MK-90) isn't implemented in current software version.

Usage hints