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**82489DX       Advanced Programmable Interrupt Controller    10/12/92
***Notes:...
***Info:...
***Versions:...
***Features:...
**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...
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*SIS...
**5595       Pentium PCI System I/O                          <12/24/97
***Notes:...
***Info:...
***Versions:...
***Features:
o   Integrated PCI-to-ISA Bridge
    − Translate s  PCI Bus Cycles into ISA Bus Cycles.   
    − Translate s ISA Master or DMA Cycles into PCI Bus Cycles.
    − Provide s 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   Supports both Desktop and Mobile Advanced Power Management Logic
    − Meets ACPI 1.0 Requirements.
    − Supports Both ACPI and Legacy PMU.
    − Supports Suspend to RAM.
    − Supports Suspend to Hard Disk.
    − Optionally Tri−state ISA bus in low power state.
    − Supports Battery Management and LB/LLB/AC Indicator.
    − Supports CPU's SMM Mode Interface.
    − Supports CPU Stop Clock.
    − Supports Power Button of ACPI.
    − Supports three system timers and SMI# watchdog timer.
    − Supports Automatic Power Control.
    − Supports Modem Ring−in, RTC Alarm Wake up.
    − Supports Thermal Detection.
    − Supports GPIOs, and GPOs for External Devices Control.
    − Supports Programmable Chip Select.
    − Supports PCI Bus Power Management Interface Spec. 1.0
    − Supports Pentium II Sleep State.
o   Enhanced DMA Functions
    − 8-, 16- bit DMA Data Transfer.
    − Two 8237A Compatible DMA Controllers with Seven Independent
      Programmable Channels.
    − Provide the Readability of the two 8237 Associated Registers.
    − Support Distributed DMA.
    − Support PC/PCI DMA.
    − Per DMA channel programmable in legacy, DDMA or PC/PCI DMA mode
      operation.
o   Integrated Two 8259A Interrupt Controllers
    − 14 Independently Programmable Channels for Level-  or Edge-
      triggered Interrupts.
    − Provide the Readability of the two 8259A Associated Registers.
    − Support Serial IRQ.
    − Support the Reroutability for the PCI Interrupts.
o   Three  Programmable 16-bit Counters compatible with 8254
    − System Timer Interrupt.
    − Generate Refresh Request.
    − Speaker Tone Output.
    − Provide the Readability of the 8254 Associated Registers.
o   Integrated Keyboard Controller
    − Hardwired Logic Provides Instant Response.
    − Supports PS/2 Mouse Interface.
    − Supports Keyboard Password Security or Hot Key Power On 
      Function.
    − Supports Hot Key "Sleep" Function.
    − Programmable Enable and Disable for Keyboard Controller and 
      PS/2 Mouse.
o   Integrated Real Time Clock(RTC) with 256B CMOS SRAM
    − Supports ACPI Day of Month Alarm/Month  Alarm.
    − Supports various Power Up events, such as Button Up, Alarm Up, 
      Ring Up, GPIO5/PME0# Up, GPIO10/ PME1# Up, Password Security Up, 
      and Hotkey Up.
    − Supports various Power Down Events, like Software Power-down, 
      Button Power-down, and ACPI S3 Power-down.
    − Supports Power Supply ’98.
    − Provides RTC year 2000 solution.
o   Integrated Frequency Ratio Control Logic for Pentium II CPU
o   Universal Serial Bus Host Controller
    − Open HCI Host Controller with Root Hub.
    − Two USB Ports.
    − Supports Legacy Devices.
    − Supports Over Current Detection.
o   Integrated Hardware Monitor Logic
    − Up to 5 Positive Voltage Monitoring Inputs.
    − Two Fan Speed Monitoring Inputs.
    − One Temperature Sensings.
    − Supports thermister- or diode- temperature sensing for Pentium 
      II CPU.
    − Threshold Comparison of all Monitored  Values.
o   Supports I2C Serial Bus/ SMBUS 
o   Supports 2MB Flash ROM Interface
o   208  pins PQFP Package
o   5V CMOS Technology

**950        LPC I/O                                         <07/16/99...
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