Sega Naomi DIMM board and GD-ROM

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DIMM board

Comes in (at least) 3 flavors.

  • GD-ROM version
  • GD-ROM with Ethernet and a serial port
  • Satellite, only ethernet

DIMM board Battery

The Naomi DIMM has a 3 wire battery pack consisting of small PCB and 2 x Panasonic CGR18650H cells. The H is probably some rating, I used CGR18650CF's which have a bit better capacity. Search for CGR18650, or just 18650 and you should be able to source some locally.

The pack is connected like this: NaomiDIMMbattery1.gif

DIMM board RAM

Samsung, 0129, Korea H, PC133U-333-532, M366S3323CT0-C7A

You can replace the orignal Samsung DIMM with 2x Samsung 256MB PC133 SDRAM 168pin DIMM M366S3323CT0-C75. Has been confirmed working and tested.

DIMM board serial interface

You can connect a computer to this port with a null-modem cable to see the VxWorks firmware bootup messages. Speed is 38400,N,8,1. To enable this, you need to change jumpers on the Naomi1 motherboard. They are located in a cluster of 3 (JP3-JP5), beneath the battery, opposite side of battery connector.

JP3 to positon 1-2 (default 2-3) enable serial receive
JP4 to positon 1-2 (default 2-3) enable serial send

Output when booting in satellite mode:

Target Name: vxTarget
User: target
Attached TCP/IP interface to lnxxx unit 0
Attaching network interface lo0... done.
NFS client support not included.


Copyright 1984-1997  Wind River Systems, Inc.

            CPU: SH7091
        VxWorks: 5.3.1
    BSP version: 1.2/1
  Creation date: Jul  4 2003
            WDB: Ready.

Set Network address from Static (not DHCP).
gcxb-1.4.3 v3.17/v3.16

Jul  4 2003 00:15:43

GD-Drive ... DISABLE
Ether ... ENABLE
CRC data broken.
pppCtrl : task spawned.
SocketControl task (Ver 3.04d) spawned.
0xcf939a4 (ComMemory): MC and BB version [HOST:0] 0x0fd00000
0xcf8e7a0 (CommRecv): spawned.
0xcf8e7a0 (CommRecv): suspended.
0xcf8bec4 (CommSend): spawned.
0xcf8bec4 (CommSend): suspended.
Memory free   240[MB]
Program size    0[MB]
Program loaded once ... NO
LAN cable ... CONNECT

DIMM board Ethernet interface

This is used for games like WCCF where you have a central node that loads games via the network instead of GD-ROM media. There is a satellite only version of the DIMM board, but all DIMM boards with Ethernet can be used. To enable satellite mode on DIMM boards, jumpers on the DIMM board must be set to:

JP1 to position 1-2
JP2 to position 1-2
JP3 to position 2-3

Network wise, this will enable TCP port 10703. Regardless of satellite mode, boards with ethernet listen on UDP port 17185 which is VxWorks WDB.

Error codes on start-up, and what they actually mean



I've seen this when the daughter board on the DIMM is not properly seated. Fix includes cleaning the contacts and re-seating.



When booting from compact flash, you get this if the card is corrupted.


Gateway is not found.

The game doesn't like the security PIC/chip you're using, or PIC is missing, only seen when net-booting(?).

GD-ROM boot sequence

  1. Security PIC is first queried for a bootstrap file name, and an 8 byte DES key
  2. DIMM board does a media check to see if a GD-ROM present
  3. The bootstrap file from step 1 is loaded from the GD-ROM
    1. Bootstrap file contains file name of the image to be loaded, and a CRC32 of this image
  4. The image file is loaded into the DIMM memory from GD-ROM, and CRC32 of the loaded data is computed
  5. When image file(game), is finished loading - the calculated CRC32 is compared to the CRC32 from the bootstrap file
  6. The system reboots, and the game starts


Sega Naomi GD-ROM Service Manual