6854 ADLC
                                =========

+--------+----------------------------+-----------------------------+
|        |      Write                 |         Read                |
+========+============================+=============================+
| base+0 | Control Register 1         | Status Register 1           |
|        |  b7: Transmit Reset        |  b7: Interupt               |
|        |  b6: Receive Reset         |  b6: Transmit Buffer Empty  |
|        |  b5: Rx Frame Discontinue  |  b5: Transmitter Underrun   |
|        |  b4: Tx Data Service Req   |  b4: Clear To Send          |
|        |  b3: Rx Data Service Req   |  b3: Flag Detected          |
|        |  b2: Tx Interupt Enable    |  b2: Loop Status            |
|        |  b1: Rx Interupt Enable    |  b1: Status Register 2 Valid|
|        |  b0: Address Control       |  b0: Receive Data Present   |
+--------+----------------------------+-----------------------------+
| base+1 | Control Register 2         | Status Register 2           |
|        |  b7: Request To Send       |  b7: Receive Data Present   |
|        |  b6: Clear Tx Status       |  b6: Receive Overrun        |
|        |  b5: Clear Rx Status       |  b5: Data Carrier Detect    |
|        |  b4: Transmit Last Data    |  b4: Frame Check Error      |
|        |  b3: Frame Complete        |  b3: Abort Received         |
|        |  b2: Idle 0=Flag/1=Idle    |  b2: Receive Idle           |
|        |  b1: 1/2-byte Transfers    |  b1: Frame Valid            |
|        |  b0: Prioritise Status     |  b0: Address Present        |
|        |                            |                             |
|        |  Control Register 3        |                             |
|        |  b7: Loop/DTR Control      |                             |
|        |  b6: Go Active On Poll     |                             |
|        |  b5: Loop/Nonloop mode     |                             |
|        |  b4: Flag Detect Enable    |                             |
|        |  b3: 01/11 Idle            |                             |
|        |  b2: Address Extend        |                             |
|        |  b1: Extended Control Field|                             |
|        |  b0: Logical Control Field |                             |
+--------+----------------------------+-----------------------------+
| base+2 | Transmit Data, Frame Cont  |                             |
+--------+----------------------------+    Receive Data Register    +
| base+3 | Transmit Data, Frame End   |                             |
+--------+----------------------------+-----------------------------+

Base  Device
------------------------------------------------------
FEA0  BBC/Master Econet Interface
FC28  Electron Econet Interface