DA11-F UNIBUS Window

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The DA11-F UNIBUS Window allows two UNIBUSes to be directly connected, to allow bus read/write cycles (including DMA cycles) from a master on one to be answered by a slave on the other; this functionality is bi-directional. Although the DA11-F can generate interrupts on either UNIBUS (in response to user commands given directly to it via its Control and Status Register), it cannot transfer interrupts (i.e. from one UNIBUS to the other).

The DA11-F responds as a slave to bus cycles on each UNIBUS which are to be passed through; it then uses an NPR DMA operation on the other UNIBUS to complete the cycle on the other, as a master. For write operations, the data is buffered in the DA11-F; therefore, simultaneous write operations on both buses can be handled.

If a read cycle is requested on one UNIBUS, and a write simultaneously on the other, the read cycle takes precedence, and is completed before the write cycle can be completed. If read cycles are requested on both buses simultaneously, neither side can gain the needed control of the other; both requests are aborted, and both cycles will time-out.

The base address, and size, of the incoming window, on each UNIBUS, is set by configuration jumpers. The base address of the outgoing window is set by a register in the BA11-F.


Registers given in italic font are read-only; those in normal font are read-write.

Register Address
Control and Status Register XXXX00
Output Data Buffer Register XXXX02
Input Data Buffer Register XXXX04
Displacement Address Register XXXX06
Relocation Address Register XXXX10
Starting Address Register XXXX12
Vector Address Register XXXX14

The first DA11-F in a system is usually assigned register addresses starting with 0764000 for the 'A' UNIBUS, and 0764020 for the 'B' UNIBUS; the second is usually assigned addresses starting with 0764020 for the 'A' UNIBUS, etc.


It consists of a 4-slot custom system unit backplane, holding two pairs of two quad cards:

  • M7284 Bus Control
  • M7283 Bus to Bus Paths

Board locations are:

Slot A B C D E F
1 UNIBUS A In M7284 A Bus Control
2 UNIBUS B Out M7283 Bus to Bus Paths (odd bits)
3 UNIBUS B In M7283 Bus to Bus Paths (even bits)
4 UNIBUS A Out M7284 B Bus Control

Further reading

  • DAll-F Unibus Window Engineering Drawings

External links