View source for RH20 MASSBUS controller

An '''RH20 MASSBUS controller''' is the primary [[secondary storage]] [[device controller]] for the later [[KL10]]s (the ones with so-called 'internal' [[main memory]]). It works with [[MASSBUS]] [[disk]] [[drive]]s and [[magnetic tape drive]]s (such as the [[RP06 disk drive|RP06]], etc, series drives); up to 8 drives per RH20.

The RH20 is connected to both the [[KL10|E Bus]] and the C Bus of the KL10; the former to allow the [[Central Processing Unit|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 [[Direct Memory Access|DMA]] to move data directly from devices to main memory, without needing CPU intervention.

==Implementation==

Each RH20 consists of a set of three [[DEC card form factor|hex]] [[printed circuit board|board]]s (M8555, M8556, 
M8557), inserted in the KL10's [[KL10#Construction|I/O backplane]] (along with the [[DTE20 Ten-Eleven Interface|DTE20s]]).

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==See also==

* [[RH10 MASSBUS controller‎]]

== External links ==

* [http://bitsavers.org/pdf/dec/pdp10/KL10/EK-RH20-UD-001_RH20_Unit_Description_Aug76.pdf RH20 Unit Description]
* [http://bitsavers.org/pdf/dec/pdp10/KL10/MP00056_RH20_Apr81.pdf RH2O Field Maintenance Print Set]
* [http://www.bitsavers.org/pdf/dec/pdp10/KL10/EK-OKL10-TM_KL10_TechRef_Aug84.pdf KL10-Based Technical Manual] (EK-OKL10-TM-002) - the RH20 is covered on pp. 102-104 of the PDF; the CBUS is covered on pp. 86-90
* [http://www.bitsavers.org/pdf/dec/pdp10/KL10/EK-1080U-SD-003_1080_1090_SysDescr_Jan77.pdf decsystem-1080/1090 System Description] (EK-1080U-SD-003) - the RH20 is covered on pp. 77-78 of the PDF
* [http://www.inwap.com/pdp10/rh20.txt Tony in RH20 Land] - An account of Tony Wachs adding RH20 support to TOPS-10.

[[Category: MASSBUS Controllers]]
[[Category: PDP-10 Peripherals]]