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x68000:xsimm10ss_-_memory_expansion_board

XSIMM10ss

The XSIMM6, XSIMM10 and XSIMM10ss all allow you to fit standard 30pin or 72pin SIMM modules to populate the address range between 2MB and 12MB on the X68000. There's a good page on the XSIMM10, as well as the XSIMM6, 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:

  • Two independent 72pin SIMM sockets (Slots A and B)
  • A pair of 30pin SIMM sockets (Slot C)

Because of this flexibility, the amount of possible configuration variations of the on board dip switches is huge.

Manual Scans

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:

Note: These images were sourced from http://painkilla.egloos.com/m/2623979

Configuration Options

Because the manual is difficult to make out, I have transcribed all of the configuration options into the table below.

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

Dip Switch G Dip Switch A DRAM Density Slot A Slot B Slot C A23-A20 Memory Size
0000 0000 4MBit - - - - -
0001 0001 4MBit 8MB - - 2 8MB
0001 0010 4MBit 8MB - - 4 8MB
0001 0011 4MBit 8MB - - 6 6MB
0001 0100 4MBit 8MB - - 8 4MB
0001 0101 4MBit 8MB - - A 2MB
0010 0001 4MBit 8MB 4/6/8MB - 2 10MB
0011 0001 4MBit 6MB - - 2 6MB
0011 0010 4MBit 6MB - - 4 6MB
0011 0011 4MBit 6MB - - 6 6MB
0011 0100 4MBit 6MB - - 8 4MB
0011 0101 4MBit 6MB - - A 2MB
0100 0001 4MBit 6MB 4/6MB - 2 10MB
0100 0010 4MBit 6MB 4/6MB - 4 8MB
0101 0001 4MBit 4MB - - 2 4MB
0101 0010 4MBit 4MB - - 4 4MB
0101 0011 4MBit 4MB - - 6 4MB
0101 0100 4MBit 4MB - - 8 4MB
0101 0101 4MBit 4MB - - A 2MB
0110 0001 4MBit 4MB 4MB - 2 8MB
0110 0010 4MBit 4MB 4MB - 4 8MB
0110 0011 4MBit 4MB 4MB - 6 6MB
0111 0001 16MBit 16MB - - 2 10MB
0111 0010 16MBit 16MB - - 4 8MB
0111 0011 16MBit 16MB - - 6 6MB
0111 0100 16MBit 16MB - - 8 4MB
0111 0101 16MBit 16MB - - A 2MB
1000 0001 16MBit 8MB - - 2 8MB
1000 0010 16MBit 8MB - - 4 8MB
1000 0011 16MBit 8MB - - 6 6MB
1000 0100 16MBit 8MB - - 8 4MB
1000 0101 16MBit 8MB - - A 2MB
1001 0001 16MBit 8MB 4/6/8MB(1,2) - 2 10MB
1010 0001 4MBit - - 2x 4MB 2 8MB
1010 0010 4MBit - - 2x 4MB 4 8MB
1010 0011 4MBit - - 2x 4MB 6 6MB
1010 0100 4MBit - - 2x 4MB 8 4MB
1010 0101 4MBit - - 2x 4MB A 2MB
1011 0001 4MBit 4/6/8MB(1,2) - 2x 4MB 2 10MB
1100 0001 1MBit - - 2x 1MB 2 2MB
1100 0010 1MBit - - 2x 1MB 4 2MB
1100 0011 1MBit - - 2x 1MB 6 2MB
1100 0100 1MBit - - 2x 1MB 8 2MB
1100 0101 1MBit - - 2x 1MB A 2MB
1101 0001 1MBit 8MB(1) - 2x 1MB 2 10MB
1110 0001 1MBit 8MB(2) - 2x 1MB 2 10MB
1111 0001 1MBit 6MB - 2x 1MB 2 8MB
1111 0010 1MBit 6MB - 2x 1MB 4 8MB
1111 1000 1MBit 4MB - 2x 1MB 2 6MB
1111 1001 1MBit 4MB - 2x 1MB 4 6MB
1111 1010 1MBit 4MB - 2x 1MB 6 6MB
1111 1011 1MBit 4MB 4MB 2x 1MB 2 10MB

You can see a few restrictions on the options:

  • If using any 72pin SIMMS, you must have Slot A filled first
  • 30pin SIMMS must always be fitted in pairs
  • You can use the following combinations:
    • Slot A
    • Slot C
    • Slot A and Slot B
    • Slot A and Slot C
    • Slot A and Slot B and Slot C (but note that there are only 2 supported configurations in that mode)
  • You cannot use the following combinations:
    • Slot B
    • Slot B and Slot C

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.

SIMM Speeds

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, so your mileage may vary if you have overclocked your CPU/bus to speeds higher than 16MHz.

Software

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, we don't know where to obtain a copy of these files.

x68000/xsimm10ss_-_memory_expansion_board.txt · Last modified: 2020/08/08 18:30 by megatron-uk