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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
***Notes:...
***Info:...
***Features:...
**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...
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**5571           (Trinity) Pentium PCI/ISA Chipset (75MHz)   <12/09/96
***Info:...
***Configurations:...
***Features:
o   Supports Intel Pentium CPU and other compatible CPU at 
    75/66/60/50MHz (external clock speed)
o   Supports the Pipelined Address Mode of Pentium CPU
o   Supports the Full 64-bit Pentium Processor data Bus
o   Supports 32-bit PCI Interface
o   Integrated Second Level (L2) Cache Controller
    - Write Through and Write Back Cache Modes
    - 8 bits or 7 bits Tag with Direct Mapped Cache Organization
    - Integrated 16K bits Dirty Ram
    - Supports Pipelined Burst SRAM
    - Supports 256 KBytes to 512 MBytes Cache Sizes
    - Cache Read/Write Cycle of 3-1-1-1-1-1-1-1 at 66 MHz
o   Integrated DRAM Controller
    - Supports 3 Banks of FP/EDO SIMMs, or 2 Banks of SDRAM DIMMs
    - Supports 2Mbytes to 384Mbytes of main memory
    - Supports 256K/512K/1M/2M/4M/16M x N FP/EDO/SDRAM DRAM
    - Supports 3V or 5V DRAM.
    - Supports Symmetrical and Asymmetrical DRAM.
    - Supports 32 bits/64 bits mixed mode configuration
    - Supports Concurrent Write Back for FP/EDO DRAM
    - Supports Mixed DRAM (FP/EDO/SDRAM) Technology
    - Supports CAS before RAS Refresh
    - Supports Relocation of System Management Memory
    - Programmable CAS# ,RAS#, RAMW# and MA Driving Current
    - Fully Configurable for the Characteristic of Shadow RAM (640 
      KBytes to 1 MBytes)
    - Supports FP DRAM 5-3-3-3(-3-3-3-3) Burst Read Cycles
    - Supports EDO DRAM 4/5-2-2-2(-2-2-2-2) Burst Read Cycles
    - Supports SDRAM 6/7-1-1-1(-2-1-1-1) Burst Read Cycles
    - Supports X-1-1-1/X-2-2-2/X-3-3-3 Burst Write Cycles
    - Supports 8 Qword Deep Buffer for Read/Write Reordering, Dword 
      Merging and 3/2-1-1-1 Post write Cycles
    - Two Programmable Non-Cacheable Regions
    - Option to Disable Local Memory in Non-Cacheable Regions
    - Shadow RAM in Increments of 16 KBytes
o   Integrated PMU Controller
    - Supports SMM Mode of CPU
    - Supports CPU Stop Clock
    - Supports Break Switch
    - Supports Modem Ring Wakeup
    - Supports Automatic Power Supply Control
o   Provides High Performance PCI Arbiter.
    - Supports 3 internal masters and 5 external  PCI Masters
    - Supports Rotating Priority Mechanism
    - Hidden Arbitration Scheme Minimizes Arbitration Overhead.
    - Supports Concurrency between CPU to Memory and PCI to PCI.
o   Integrated Host-to-PCI Bridge
    - Supports Asynchronous/Synchronous PCI Clock
    - Translates the CPU Cycles into the PCI Bus Cycles
    - Provides CPU-to-PCI Read Assembly and Write Disassembly 
      Mechanism
    - Translates Sequential CPU-to-PCI Memory Write Cycles into PCI 
      Burst Cycles
    - Zero Wait State Burst Cycles
    - Supports 8 DW Deep Buffer for CPU-to-PCI Posted Write Cycles
    - Supports Pipelined Process in CPU-to-PCI Access
    - Supports Advance Snooping for PCI Master Bursting
    - Maximum PCI Burst Transfer from 256 Bytes to 4 Kbytes
    - Fast back-to-back
o   Integrated Posted Write Buffers and Read Prefetch Buffers to 
    Increase System Performance
    - CPU-to-Memory Posted Write Buffer (CTMFF) with 8 QW Deep, Always 
      Sustains 0 Wait Performance on CPU-to-Memory.
    - CPU-to-PCI Posted Write Buffer(CTPFF) with 8 DW Deep
    - PCI-to-Memory Posted Write Buffer(PTHFF) with 8 QW Deep, Always 
      Streams 0 Wait Performance on PCI-to/from-Memory Access
    - PCI-to-Memory Read Prefetch Buffer(CTPFF) with 8 QW Deep
o   Built-in one 32-bit General Purpose Register
o   Integrated PCI-to-ISA Bridge
    - Translates PCI Bus Cycles into ISA Bus Cycles
    - Translates ISA Master or DMA Cycles into PCI Bus Cycles
    - Provides a Dword Post Buffer for PCI to ISA Memory cycles
    - Two 32 bit Prefetch/Post Buffers Enhance the DMA and ISA Master 
      Performance
    - Fully Compliant to PCI 2.1
o   Enhanced DMA Functions
    - 8-, 16- bit DMA Data Transfer
    - ISA compatible, and Fast Type F DMA Cycles
    - Two 8237A Compatible DMA Controllers with Seven Independent 
      Programmable Channels
    - Provides the Readability of the two 8237 Associated Registers
o   Built-in Two 8259A Interrupt Controllers
    - 14 Independently Programmable Channels for Level- or Edge-
      triggered Interrupts
    - Provides the Readability of the two 8259A Associated Registers
o   Three Programmable 16-bit Counters compatible with 8254
    - System Timer Interrupt
    - Generates Refresh Request
    - Speaker Tone Output
    - Provides the Readability of the 8254 Associated Registers
o   Built-in Keyboard Controller
    - Hardwired Logic Provides Instant Response
    - Supports PS/2 Mouse
    - Support Hot Key "Sleep" Function
o   Built-in Real Time Clock(RTC) with 256B CMOS SRAM
o   Fast PCI IDE Master/Slave Controller
    - Fully Compatible with PCI Local Bus Specification V2.1
    - Supports PCI Bus Mastering
    - Plug and Play Compatible
    - Supports Scatter and Gather
    - Supports Dual Mode Operation - Native Mode and 
      Compatibility Mode
    - Supports IDE PIO Timing Mode 0, 1, 2 of ANSI ATA Specification
    - Supports Mode 3 and Mode 4 Timing Proposal on Enhanced IDE 
      Specification
    - Supports Multiword DMA Mode 0, 1, 2
    - Separate IDE Bus
    - Two 8x32-bit FIFO for PCI Burst Read/Write Transfers.
o   Universal Serial Bus Controller
    - Host/Hub Controller
    - Two USB ports
o   On-Board Plug and Play Support
    - One Steerable DMA Channel
    - One Steerable Interrupt
    - One Programmable Chip Select
o   Supports the Reroutibility of the four PCI Interrupts
o   Supports Flash ROM
o   480-Pin BGA Package
o   0.5 μm CMOS Technology

**5581/5582      (Jessie)  Pentium PCI/ISA Chipset (75MHz)   <04/15/97...
**5591/5592/5595 (David)   Pentium PCI A.G.P. Chipset        <01/09/98...
**5596/5513      (Genesis) Pentium PCI Chipset               <03/26/96...
**5597/5598      (Jedi)    Pentium PCI/ISA Chipset           <04/15/97...
**530/5595       (Sinbad) Host, PCI, 3D Graphics & Mem. Ctrl.<11/10/98...
**540            (Spartan) Super7 2D/3D Ultra-AGP Single C.S.<11/30/99...
**55x            SoC (System-on-chip)                        <03/14/02...
**
**Support chips:
**85C206     Integrated Peripheral Controller [no datasheet]         ?...
**5595       Pentium PCI System I/O                          <12/24/97...
**950        LPC I/O                                         <07/16/99...
**Other:...
**PII/III/Pro...
**Athlon etc...
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*UMC...
*Unresearched:...
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*ZyMOS...
*General Sources:...