DIA20 IBus Adapter

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The DIA20 IBus Adapter (sometimes called the DIA20 In/Out Bus Controller) is an optional controller on KL10 CPUs which provides an old-style PDP-10 I/O Bus (termed an 'IBus'), to allow existing PDP-10 peripherals to be used on one. Two separate IBuses are provided per CPU. (In a multi-processor system, each CPU has a separate DIA20, if configured to have one.) Later KL10s did not normally include the backplane into which the DIA20 plugged; that backplane together with a DIA20 were denominated a DIB20.


The DIA20 is connected to the EBox of the KL10 via the EBus; when no other controller on the EBus responds to a command, the DIA20 will respond, and send the command out the IBus. Similarly, interrupt requests from IBus devices are sent through to the EBox.

It consists of a number of hex boards (two M8550s and an M8551) plugged into an I/O backplane (one shared with the DMA20 Memory Bus Adapter‏‎) of the KL10; these are connected to new-style I/O bus connectors mounted lower down in that rack.

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