IBM SIMM RAM modules in FM Towns

Started by Tw3ek, September 16, 2016, 01:25:51 AM

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I looked around and couldn't find any of this information not in Japanese, so I thought I would share it here in case anyone else was looking to add extra RAM to their FM Towns. The first step is finding a compatible RAM SIMM module. You will need a SIMM module WITHOUT ECC (non-parity) and non-EDO, as those will not work in the Towns. You can use this link to find the required timing and the maximum capacity for memory depending on your model of FM Towns. For this specific example. I used an ME20 which has a maximum of 32MB per slot and requires 80ns or less for timing. Pins 67-70 on SIMM RAM modules are the ID pins, to tell how much capacity the memory has. The FM Towns uses the following setup for those pins:

Where X indicates an open connection and O indicates a connenction to GND. On an IBM PC SIMM module, all 4 of those pins will be connected, but those connections may vary. Some have all 4 on one side, others have the connections for 67 and 69 on one side and 68 and 70 on the other.

Here you can see the connections for pins 67 and 69. This is a 32MB RAM module, so both of these connections should be desoldered or removed, as well as the connection to pin 70 on the reverse side.  Leave the connection for pin 68 alone, as that is connected to GND by default. Once you have the appropriate connections removed, you're finished! Drop it in your FM Towns and enjoy!