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**82485       Turbo Cache (and 485Turbocache)                      c90
***Notes:...
***Info:
The 82485 is  a second-level cache controller designed  to improve the
performance  of  Intel486  Microprocessor  systems.  One  82485  cache
controller supports  64K or  128K bytes of  second level  cache memory
that maps  to the  entire 4 Gigabytes  of the  Intel486 microprocessor
address space. The controller  is completely software transparent. One
controller plus SRAMs  provides a 64K or a  128K cache. External EPROM
can  be  cached  yet  remain  write protected.   The  82485  is  fully
compatible  with the  Intel486  microprocessor. All  Intel486 CPU  bus
cycles and timings are supported.

A complete, optional second level  cache controller using the 82485 is
available  as the 485Turbocache  Module from  Intel (data  sheet order
number 240722).

2.0 FUNCTIONAL DESCRIPTION
2.1 Introduction
The 82485 is a single ported, two-way set associative cache controller
designed specifically  to interface with  the Intel486 microprocessor.
The controller supports either a sectored configuration (two lines per
tag) or  a non-sectored configuration  (one line per tag).   The 82485
will directly support a nonsectored  64K data cache or a 128K sectored
data cache.  Both the 64K and  128K configurations are able to map the
entire 4 gigabytes of  the Intel486 microprocessor address space.  The
82485 interfaces directly to  the Intel486 microprocessor.  All Intel-
486 CPU bus cycles and timings are supported.  The 82485 also supports
0 wait  state processor operation  when there is  a cache hit  and has
provisions to support invalidation cycles, BOFF# cycles, and premature
BLAST# terminations.  The controller  is look aside (monitors bus act-
ivity in parallel to the processor) and write through (all writes pro-
pagate to the  system bus), so it supports  the same cache consistency
mechanisms as the  Intel486 CPU.  The controller also  provides a safe
method to cache ROM BIOS through the  use of a write protect pin and a
write protect strapping option.

The data cache  (Static RAM) resides external to  the 82485. The 82485
provides all  controls for  the SRAMs.  No  external latches  or tran-
ceivers are  required.  The 82485  output buffers support up  to eight
SRAMs.  A  64K cache can be  designed with only  five components; nine
components for a 128K cache.  Two-way set associativity is provided by
dual banked SRAMs. Data parity is supported.

The  82485  can  be  used  to  design  a  custom  second  level  cache
configuration. For an easier system design and higher integration, the
82485M Turbocache  can be used  (see data sheet order  number 240722).
This  module is  a  complete second  level  cache in  one package.  It
consists  of a single  82485 cache  controller and  SRAM to  provide a
complete 64K or 128K second level Intel486 microprocessor second level
cache.

***Versions:...
***Features:...
**82489DX       Advanced Programmable Interrupt Controller    10/12/92...
**82495DX/490DX DX CPU-Cache Chip Set                           <Sep91...
**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
***Notes:
Date source: 1995_Intel_Pentium_Processors_and_Related_Components.pdf

Information taken from: 
            1995_Intel_Pentium_Processors_and_Related_Components.pdf*
                                         8249x Cache controllers.pdf**
>*  Datasheet dated Nov'94
>** Datasheet undated, whole document dated '95

The info and features section have  been solely sourced from the first
source.   The  second source  provides  far  more detail.   Additional
information in the configurations section  and below have been sourced
from the second.

"Although the 82497 Cache Controller  is part of the Pentium processor
(735\90, 815\100, 1000\120, 1110\133) CPU-Cache Chip Set and the 82496
Cache  Controller is part  of the  Pentium Processor  (510\60, 567\66)
Chip  Set, the  two parts  are functionally  identical except  for the
differences noted in this section." - p491

Aside  from some  minor  differences in  pin  configuration, the  main
difference is the direct support  for 3.3V processors. This chipset is
still a 5V part. The cache operates at bus speed, max 66MHz.


This  chip was  used on  the Pentium  90MHz CPU  complexes of  Intel's
Xpress  platform.   Specifically  the BXCPUPENT90  (Single  90MHz,  16
82492s). Also found on IBM 9595/Server 500 Pentium 90MHz complexes.

***Info:...
***Configurations:...
***Features:...
**82498/493   Cache Controller / Cache RAM (for P54 Pentium)    <Nov94...
**
**Later chipsets (basic spec):
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**450NX  (?)            06/29/98:...
**?????  (Profusion)    c:99...
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