9914 IEEE General Purpose Interface Bus
                =======================================

+--------+--------------------------+----------------------------------+
|        |          Write           |               Read               |
+========+==========================+==================================+
| base+0 | Interupt Mask 0          | Interupt Status 0                |
|        |  b7: -                   |  b7: Int pending in Int Status 0 |
|        |  b6: -                   |  b6: Int pending in Int Status 1 |
|        |  b5: BI Int Enable       |  b5: Byte In: Data In Full       |
|        |  b4: BO Int Enable       |  b5: Byte Out: Data Out Empty    | 
|        |  b3: END Int Enable      |  b3: Received byte last in string|
|        |  b2: SPAS Int Enable     |  b2: Serial Poll Service         |
|        |  b1: RLC Int Enable      |  b1: Remote/Local Change         |
|        |  b0: MAC Int Enable      |  b0: My Address Change           |
| base+1 | Interupt Mask 1          | Interupt Status 1                |
|        |  b7: GET Int Enable      |  b7: Group Execture Trigger      |
|        |  b6: ERR Int Enable      |  b6: Error                       |
|        |  b5: UNC Int Enable      |  b5: Unrecognised Command        |
|        |  b4: APT Int Enable      |  b4: Address Pass Through        |
|        |  b3: DCAS Int Enable     |  b3: Device Clear Active State   |
|        |  b2: MA Int Enable       |  b2: My Address recognised       |
|        |  b1: SQR Int Enable      |  b1: Service Request             |
|        |  b0: IFC Int Enable      |  b0: Interface Clear             |
| base+2 | -                        | Address Status                   |
|        |                          |  b7: Remote State                |
|        |                          |  b6: Local Lockout               |
|        |                          |  b5: Attention line low          |
|        |                          |  b4: Listener Primary state      |
|        |                          |  b3: Talker Primary state        |
|        |                          |  b2: Is addressed to listen      |
|        |                          |  b1: Is addressed to talk        |
|        |                          |  b0: LSB of last addr recognised |
| base+3 | Auxilary Control         | Bus Status                       |
|        |  b7: Clear/Set function  |  b7: ATN                         |
|        |  b6: -                   |  b6: DAV                         |
|        |  b5: -                   |  b5: NDAC                        |
|        |  b0-4: Function          |  b4: NRFD                        |
|        |                          |  b3: EOI                         |
|        |                          |  b2: SQR                         |
|        |                          |  b1: IFC                         |
|        |                          |  b0: REN                         |
| base+4 | Address                  | -                                |
|        |  b7: Enable Dual Primary |                                  |
|        |  b6: Disable Listener    |                                  |
|        |  b5: Disable Talker      |                                  |
|        |  b0-4: Address A1-A5     |                                  |
| base+5 | Serial Poll              | -                                |
|        |  b7: S8                  |                                  |
|        |  b6: Requast Service b1  |                                  |
|        |  b0-5: S1-S6             |                                  |
| base+6 | Parallel Poll Data       | Command Pass Through             |
| base+7 | Data Out                 | Data In                          |
+--------+--------------------------+----------------------------------+
NOTE: TMS Documentation labels the data bus D7-D0 instead of D0-D7.
This lists individual bits the correct way around, as they appear on
the data bus.

Base  Device
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FC20  IEEE Interface