Details on the 3DO XBUS / Opera Expansion Bus. The CDROM drive, VCD adapter, and Memory Expansion were the only devices that utilized the bus though other devices such as modems, hard drives, set top boxes, etc. were discussed or in the works.

====== Patent ======

{{:documentation:patents:wo09416382a1_-_expansion_bus.pdf|WO09416382A1 - Expansion Bus}}

====== Pinout ======

^ Pin ^ Signal ^ I/O ^ Description ^
| 1 | ADB[0] | I/O | Bi-directional Address and Data Bus (tri-state outputs) |
| 2 | ADB[1] |   |   |
| 3 | ADB[2] |   |   |
| 4 | GND |   |   |
| 5 | ADB[3] |   |   |
| 6 | ADB[4] |   |   |
| 7 | ADB[5] |   |   |
| 8 | GND |   |   |
| 9 | ADB[6] |   |   |
| 10 | ADB[7] |   |   |
| 11 | INT- | O | Interrupt signal. Indicates drive has data or status information ready for transfer. (Open collector output) |
|  |  |  |  |
| 12 | GND |   |   |
| 13 | STB- | I | Strobe signal. Used to indicate all address, data, and command transfers on the Opera Expansion Bus. |
| 14 | CMD- | I | Command signal. Used in conjunction with the SEL- and WR- signals to determine the transaction type. |
| 15 | RDY- | O | Ready signal. Indicates the expansion device has placed data onto the ADB bus. Also used to indicate media access (door open/close events) (Tri-state output). |
| 16 | GND |   |   |
| 17 | SEL- | I | Selection signal. Used in conjunction with the CMD- and WR- signals to determine the transaction type. |
| 18 | WR- | I | Write signal. Indicates command, data, or address information will be transferred from the Opera System to the expansion device. Used in conjunction with the SEL- and CMD- signals to determine the transaction type. |
| 19 | IDIN | I | Input from previous expansion device. Used for device address assignment. |
| 20 | IDOUT | O | Output to next expansion device. Used for device address assignment. |
| 21 | RESET- | I | Power On Reset signal driven by the Opera System. |
| 22 | GND |   |   |
| 23 | reserved |   |   |
| 24 | reserved |   |   |
| 25 | POWER | O | Output to turn on expansion device. Provides a total of 40 mA of 4.5 to 5.5 Volts. This signal is intended to control a power relay in the expansion device. |
| shield | chassis GND |   |   |

====== Transactions ======

From page 11 of the patent

^  SEL-  ^  CMD-  ^  WR-  ^  Transaction  ^  Operation  ^
| 0 | 0 | 0 | WR_POL | Opera System performing a write to the expansion device's Poll Register |
| 0 | 0 | 1 | RD_POL | Opera System performing a read of the expansion device's Poll Register |
| 0 | 1 | 0 | SELECTION | Opera System performing a selection of an expansion device |
| 0 | 1 | 1 | Reserved |  |
| 1 | 0 | 0 | WR_COM | Opera System performing a write of a command byte to the expansion device |
| 1 | 0 | 1 | RD_STAT | Opera System performing a read of the expansion device's status |
| 1 | 1 | 0 | WR_DATA | Opera System performing a write of a data byte to the expansion device |
| 1 | 1 | 1 | RD_DATA | Opera System performing a read of a data byte from the expansion device |