KUV11 Writeable Control Store

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The KUV11 Writeable Control Store is an option for the LSI-11 which provides a user-programmable microcode memory extension, along with some hardware aids to debugging micro-programs. It allows additional, custom instructions to be added to the PDP-11 instruction set.

It consists of a quad card (M8018) which plugs into the QBUS backplane close to the CPU card, and a flat cable which runs from the KUV11 to a free micro-ROM chip socket on the CPU card, and gives the KUV11 access to the micro-instruction bus.

The micro-store consists of 24 1Kx1 high-speed static RAM chips. The LSI-11 micro-word is 22 bits long; the extra two bits are fed to backplane pins (AE1 and AF1) to provide high-speed controls. A DIP switch on the KUV11 controls where the micro-store appears in the micro-address space.

The micro-words themseves are fed to the LSI-11 over the cable; the LSI-11 does not have the ability to write the micro-store contents over that cable, but has read-write access to it via the QBUS. That bus also provides access to a number of control registers on the KUV11.

The principle hardware debugging aid is the 'micro-address trace RAM', which is a 16-entry record of consecutive micro-addresses emitted as the micro-program runs, which can be frozen under program control, using one of the two extra bits in the extended micro-word.

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