RH20 MASSBUS controller

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An RH20 MASSBUS controller is the primary secondary storage device controller for the later KL10s (the ones with so-called 'internal' main memory). It works with MASSBUS disk drives and magnetic tape drives (such as the RP06, etc, series drives); up to 8 drives per RH20.

The RH20 is connected to both the E Bus and the C Bus of the KL10; the former to allow the CPU to control it. and the latter to give the RH20 direct access to the main memory of the system, to allow it to use DMA to move data directly from devices to main memory, without needing CPU intervention.


Each RH20 consists of a set of three hex boards (M8555, M8556, M8557), inserted in the KL10's I/O backplane (along with the DTE20s).

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