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**82495DX/490DX DX CPU-Cache Chip Set                           <Sep91
***Notes:...
***Info:
The 50 MHz Intel486 DX  CPU-Cache Chip Set provides a high performance
solution  for  servers  and  high-end desktop  systems.   This  binary
compatible solution  has been optimized  to provide 50 MHz,  zero wait
state performance. The CPU-Cache chip set combines the 50 MHz Intel486
Microprocessor with  the 82495DX/82490DX cache  subsystem. It delivers
integer  performance of  41 V1.1  Dhrystone  MlPs and  a SPEC  integer
rating  of  27.9.  The  cache  subsystem  features  the 82495DX  Cache
Controller and the 82490DX Dual  Ported Data RAM.  Dual ported buffers
and registers  of the  82490DX allow the  82495DX Cache  Controller to
concurrently handle CPU bus, memory bus, and internal cache operations
for maximum performance.

The CPU-Cache Chip Set offers  many features that are ideal for multi-
processor  based systems.  The  Write-Back feature  provides efficient
memory  bus utilization  by reducing  bus traffic  through eliminating
unnecessary  writes  to main  memory.   The  CPU-Cache  chip set  also
supports MESI protocol and monitors  the memory bus to guarantee cache
coherency.

The 50  MHz Intel486  DX CPU and  82495DX/82490DX Cache  subsystem are
produced on  Intel's latest CHMOS  V process which  features submicron
technology and triple layer metal.

3.0 ARCHITECTURAL OVERVIEW
3.1 Introduction
The Intel486 CPU-cache chip  set provides a tightly coupled processing
engine  based on  the Intel486  microprocessor and  a  cache subsystem
comprised of  the 82495DX cache controller and  multiple 82490DX cache
components.   Figure 3.1  [see datasheet]  diagrams the  basic config-
uration.

The cache subsystem provides a  gateway between the CPU and the memory
bus. All CPU accesses that  can be serviced locally are transparent to
the memory bus and serve to avoid bus traffic.  As a result, the cache
chip  set  reduces memory  bus  bandwidth  to  both increase  Intel486
processor  performance and  support efficient  multiprocessor systems.
The  cache subsystem also  decouples the  CPU from  the memory  bus to
provide  zero-wait-state  operation at  high  clock frequencies  while
allowing relatively slow and inexpensive memories.

The  CPU-cache chip  set  prevents latency  and bandwidth  bottlenecks
across  a variety  of  uniprocessor and  multiprocessor designs.   The
processor’s  on-chip cache  supports  a  very wide  CPU  data bus  and
high-speed data  movement. The second-level cache  greatly extends the
capabilities of the on-chip cache resources, enabling a larger portion
of memory cycles to be satisfied independently of the memory bus.

3.2 CPU-Cache Chip Set Description
The chip set is comprised of three functional blocks: 

3.2.1 CPU
The chip  set includes a  special version of the  Intel486DX micropro-
cessor at  50 MHz.  The Intel486DX Microprocessor  Data Sheet provides
complete component specifications.

3.2.2 CACHE CONTROLLER
The 82495DX cache controller is  the main control element for the chip
set. providing  tags and line  states. and determining cache  hits and
misses. The 82495DX executes all  CPU bus requests and coordinates all
main memory accesses with the memory bus controller (MBC).

The 82495DX  controls the data  paths of the 82490DX  cache components
for cache hits and misses and furnishes the CPU with needed data.  The
controller  dynamically adds  wait  states as  needed  using the  most
recently used (MRU) prediction algorithm.

The 82495DX also performs memory bus snoop operations in shared memory
systems  and drives  the  cycle address  and  other attributes  during
memory bus accesses. Figure  3.2 [see datasheet] diagrams the 82495DX.

3.2.3 CACHE SRAM

Multiple  82490DX cache  components provide  the cache  SRAM  and data
path. Each component  includes the latches, muxes and  logic needed to
work in lock  step with the 82495DX to efficiently  serve both hit and
miss  accesses.  The 82490DX  components take  full advantage  of VLSI
silicon   flexibility   to  exceed   the   capabilities  of   discrete
implementations.  The  82490DX components support  zero-wait-state hit
accesses  and  concurrent  CPU  and  memory  bus  accesses,  and  they
replicate MRU  bits for autonomous  way prediction. During  memory bus
cycles. the 82490DX components act as a gateway between CPU and memory
buses. Figure 3.3 [see datasheet] diagrams an 82490DX cache component.

3.3 Secondary Cache Features

The 82495DX  cache controller and  82490DX cache components  provide a
unified, software  transparent secondary  data and  instruction cache.
The cache enables  a highspeed processor core  that provides efficient
performance even when paired with a significantly slower memory bus.

The secondary  cache interprets  CPU bus cycles  and can  service most
memory read and  write cycles without accessing main  memory.  I/O and
other special cycles are passed directly to the memory bus.  The cache
has a dual-port  structure that permits concurrent CPU  and memory bus
operation.

The 82495DX  cache controller  contains the 8K  tag entries  and logic
needed to support a cache as  large as 256K. Combinations of between 4
and 9 82490DX cache SRAMs are  used to create caches ranging from 128K
to 256K, with or without data parity.

The  MBC provides  logic  needed  to interface  the  CPU, 82495DX  and
82490DX  to the  memory  bus.   Because the  MBC  also affects  system
performance.  its design can be the basis of product differentiation.

***Configurations:...
***Features:...
**82495XP/490XP Cache Controller / Cache RAM (for i860)       06/05/91...
**82496/491     Cache Controller / Cache RAM (for P5 Pentium) 03/22/93...
**82497/492   Cache Controller / Cache RAM (for P54 Pentium)    <Nov94...
**82498/493   Cache Controller / Cache RAM (for P54 Pentium)    <Nov94...
**
**Later chipsets (basic spec):
**440 series:...
**450NX  (?)            06/29/98:...
**?????  (Profusion)    c:99...
**800 series...
*Headland/G2...
*HMC (Hulon Microelectronics)...
*Logicstar...
*Motorola...
*OPTi...
**82C601/2       Buffer Devices                                 <Nov94
***Info:...
***Versions:...
***Features:...
**82C822         PCIB (VLB-to-PCI bridge)                         c:94...
**Other:...
*PC CHIPS/Amptron/Atrend/ECS/Elpina/etc...
*SIS...
*Symphony...
*TI (Texas Instruments)...
*UMC...
*Unresearched:...
*VIA...
*VLSI...
**VL82C031/032/033      PS/2 Model 30-compatible chip set          c88
***Notes:...
***Info:
The chip set  integrates logic on PS/2 Model  30-Compatible systems to
the point of  reducing the printed circuit board device  count by half
when  memories   are  excluded.   Further,  while   offering  complete
compatibility with the PS/2 Model  30-Compatible system, the VLSI chip
set improves system  performance by allowing 10 MHz  operation with no
"wait states" (using 150 ns DRAMs), supports an additional 8M bytes of
memory  using EMS  (Expanded Memory  Specification) 4.0,  and controls
system speed as necessary for optimum performance.

A third  device the  VL82C037 VGA Video  Graphics Controller,  is also
used  in  the  PS/2  Model  30-Compatible  system  and  provides  high
resolution graphics of up to 800  x 600 pixels with 16 colors. Graphic
capabilities  with this  resolution  are usually  found  only on  more
expensive systems.

The VL82C031  provides the PS/2  Model 30-Compatible system  with dual
speed  control,  8 MHz  or  10  MHz, to  operate  the  system at  peak
performance.  The device  also controls  memory, I/O,  parity, address
paths, and  data paths  as well  as handling  four channels  of direct
memory access. The VL82C031 is available from VLSI Technology, Inc. in
an industry-standard plastic 100-pin flatpack.

The CMOS VL82C031 is the System Controller device in the two-chip VLSI
PS/2 Model 30-Compatible chip set.

The  chip can  be  brought  to a  power-down  mode  to conserve  power
dissipation when static RAM is used. The chip can then be woke up from
power-down mode by an external interrupt.

The VL82C032 provides the PS/2 Model 30-Compatible system with control
of both the keyboard and the pointing device ("mouse"), control of two
serial  communi-  cation  channels,  a real-time  clock,  as  well  as
controlling  both the  disk  storage and  display  functions. It  also
provides  the chip  select logic  for the  functions in  controls. The
VL82C032  is available  from VLSI  Technology, Inc.   in an  industry-
standard plastic 100-pin flatpack.

The  CMOS  VL82C032  is  the Input/Output  Controller  device  in  the
two-chip VLSI PS/2 Model 30-compatible chip set.

[The following text is from the '88 version:]

The VL82C033/OTi-033 is the Floppy  Disk Controller and Data Separator
device  in  the three  chip  VLSI/OTi  PS/2 Model  30-Compatible  chip
set. The other two devices  are the VL82C031/OTi-031 System Controller
and the VL82C032/OTi-032 I/O Controller.

The VL82C033/OTi-033 provides the PS/2 Model 30-Compatible system with
a uPD  756A- compatible floppy  disk controller function,  a precision
analog  data separator,  an  internal phase  comparator, the  required
filters,  as  well as  a  voltage  controlled oscillator  (VCO).   The
VL82C033/OTi-033  provides the  system with  three floppy  disk rates:
250K bits-per-second, 300K bits-per-second, and 500K bits-per- second.
the VL82C033/OTi-033 is available form  both VLSI Technology, Inc. and
Oak Technology, Inc.  in an industry-standard plastic 48 pin DIP.

***Configurations:...
***Features:...
**VL82C286-SET     TOPCAT 286/386SX PC/AT-Compatible Chip Set        ?...
**VL82C386-SET     TOPCAT 386DX PC/AT-Compatible Chip Set            ?...
**VL82C386sx-SET   TOPCAT 286/386SX PC/AT-Compatible Chip Set        ?...
**VL82C310         SCAMP-LT                                          ?...
**VL82C311         SCAMP-DT                                          ?...
**VL82C311L        SCAMP-DT 286                                      ?...
**VL82C312         SCAMP Power Management Unit (PMU)                 ?...
**VL82C315A        SCAMP II, Low-Power Notebook Chipset              ?...
**VL82C322A        SCAMP II, Power Management Unit (PMU)             ?...
**VL82C316         SCAMP II, PC/AT-Compatible System Controller      ?...
**VL82C323         SCAMP II, 5 Volt Power Management Unit (PMU)      ?...
**VL82C380         Single chip 386DX PC/AT Controller +on-chip cache ?...
**VL82C325             VL82C386SX System Cache controller            ?...
**VL82C335             VL82C386DX System Cache ctrl. [no d.sheet]    ?...
**VL82C315A/322A/3216  Kodiak 32-Bit Low-Voltage Chip Set            ?...
**VL82C420/144/146     SCAMP IV [no datasheet, some info]          c93...
**VL82C480         System/Cache/ISA bus Controller                   ?...
**VL82C481         System/Cache/ISA bus Controller                 c92...
**VL82C486         Single-Chip 486, SC486, Controller                ?...
**VL82C425         486 Cache controller                              ?...
**????????         Cheetah 486, PCI [no datasheet]                   ?...
**VL82C3216        Bus Expanding Controller Cache with write buffer  ?...
**VL82C521/522     Lynx/M                                            ?...
**VL82C530         Eagle Ð                                         c95...
**VL82C541/543     Lynx                                            c95...
**VL82C591/593     SuperCore 590                                   c94...
**VL82C594/596/597 Wildcat                                         c95...
**I/O Chips:
**VL82C106 Combination I/O chip                                      ?...
**VL82C107 SCAMP  Combination I/O chip                               ?...
**VL82C108 TOPCAT Combination I/O chip                               ?...
**VL82C110 Combination I/O chip                                      ?...
**VL82C113 SCAMP  Combination I/O chip                               ?...
**VL82C114 Combination I/O chip                                      ?...
**Video: ...
**Disk:...
**Modems:...
**Other:...
**Not sure if they actually exist...
*Western Digital...
*Winbond...
*ZyMOS...
*General Sources:...

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