Jnc: Fairly complete (for a start)

2024-11-27T17:49:40Z

Fairly complete (for a start)

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The '''KA820 CPU''' is a mid-range [[VAX]] [[Central Processing Unit|CPU]] used in [[VAX 82xx/83xx series]] systems. It, and they, use the [[VAX Bus Interconnect|VAXBI]] [[bus]] to connect their main sub-systems, including the [[main memory]]. The CPU also supports the PCI bus (apparently un-related to the bus of the [[Peripheral Component Interconnect|same name]] on [[IBM-compatible PC]]s), used to connect local, low-speed [[peripheral|devices]].

It used the V-11 [[integrated circuit|chip]] set (code named 'Scorpio'), fabricated in-house using [[Metal Oxide Semiconductor|MOS]] technology. It made extensive use of [[pipeline|pipelining]] internally; operation throughout the CPU is extensively protected by [[parity]].

Physically, the KA820 is a single [[printed circuit board|board]] containing a number of custom [[VLSI]] chips: one for [[instruction]] decoding and [[execute|execution]]; one for [[memory management]] and [[cache]] management; one for [[floating point]]; and the VAXBI interconnect interface chip (BIIC). A separate cache is also provided for main memory; another cache, the backup translation buffer (BTB), holds [[page table]] entries (this supplements a 'mini-translation buffer' (MTB) held directly on the memory management chip).

The KA820 is a [[microcode]]d CPU, using 40-bit micro-instructions. The microcode is mostly held in [[read-only memory|ROM]], but a novel scheme involving a [[content-addressable memory|CAM]] allows it to be 'patched', using a small amount of [[Random Access Memory|RAM]]. An [[EEPROM]] holds microcode patches, along with configuration settings, across power-down/up cycles. [[Front panel]] functionality is also provided by microcode, along with an on-board [[asynchronous serial line]] interface.


==External links==

* [http://www.bitsavers.org/pdf/dec/vax/8200/ 8200] - documentation at [[Bitsavers]]
** [http://www.bitsavers.org/pdf/dec/vax/8200/KA820-AA.TXT KA820-AA Specification - Part II - User and Programming Information]
* [http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/EK-KA820-TM-003%20KA820-KA825%20Processor%20Technical%20Manual.pdf KA820/KA825 Processor Technical Manual] (EK-KA820-TM-003)
* [https://en.wikipedia.org/wiki/DEC_V-11 DEC V-11]
* [https://simh.trailing-edge.com/semi/v11.html V-11 (1986)]

[[Category: DEC VAX Processors]]
[[Category: VAX 82xx/83xx Systems]]
[[Category: VAXBI]]

KA820 CPU - Revision history

Jnc: Fairly complete (for a start)