Sharp X68000 - TSR XSIMM10ss Memory Expansion Board

The X68000 has a 24bit address bus, which means it can address up to 16MB of RAM, however part of that address space is taken up by video memory and other memory mapped IO ranges, other than the 32bit 68030 models, all X68000 models can have up to 12MB of RAM.

The first 2MB of RAM is always on the motherboard; either directly attached (in some later models like the XVI), or as 1MB directly attached chips with a 1MB upgrade card. Anything above that comes via the IO slots.

The XSIMM6, XSIMM10 and XSIMM10ss all allow you to fit standard 30pin or 72pin SIMM modules to populate that address range between 2MB and 12MB. There's a good page on the XSIMM10, as well as the XSIMM6 at Gamesx, but both boards are comparatively simple compared to the XSIMM10ss.

Unfortunately, information on the later XSIMM10ss is rather thin on the ground - which is a shame as it has the most flexibility of all the models:

• A pair of 30pin, 16bit SIMM sockets
• Two independent 32bit, 72pin SIMM sockets

These are the only copies of the manual I've been able to find - they are different to the XSIMM10 which does not have the 72pin sockets:

Images sourced from: http://painkilla.egloos.com/m/2623979

Because there is a mix of 30pin (16bit each) and 72pin sockets (32bit each), there is an insane number of possible configurations that you can set the board up to use.

Note: 'Memory Size' in the below table refers to the expansion memory size, not the entire system memory size.

There are a couple of variations of the same sizes - they are:

• (1) 4MBit DRAM density
• (2) 16MBit DRAM density

Note: If you want to max out the memory capacity, by far the simplest option is to stick a single 16MB 72pin SIMM in slot A.

All standard 10MHz X68000 models can use 80ns, 70ns or 60ns chips, according to the manual, but at 16MHz, it requires 70ns or faster. There aren't any details for models clocked higher than that (which, apart from the Red Zone overclocked models, don't exist anyway).

The manual also makes reference to an xsimm.x utility, but I can't quite make out what it is supposed to do - whether it tests the onboard ram or is just documentation. As it stands, I don't know where to obtain a copy of these files.