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**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...
**
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**SL82C465    Cache Controller (for 486/386DX/SX)                 c:91
***Info:
The SL82C465 cache controller supports both 1X and 2X clock modes. The
1X clock  mode means that the CCLK2  signal is used as  the CPU clock;
the 2X clock  mode means that the PCLK signal  (half the frequency and
the phase indicator  of CCLK2) is used as the  CPU clock. The SL82C465
and other CPU local bus devices run at the same clock frequency as the
CPU, while  the rest of the system  runs at the frequency  of PCLK. In
other words, the operating frequency of the system logic is either the
same (2X clock mode) or half the speed of the CPU (1X clock mode). For
the 1X clock mode, the timing of the signals between the CPU/Cache and
the system logic interface  is converted by the SL82C465 automatically
to  satisfy  the requirement  of  individual  clocks.  Table 1-1  [see
datasheet] lists  the operating frequencies  of the CPU local  bus and
the system logic with the oscillator used.

The 2X  clock mode is recommended  for a CPU frequency  no faster than
33Mhz because the system logic  is available at the targeted speed and
the  performance  is  slightly  better  than if  1X  clock  mode  were
used. For  a CPU  frequency faster  than 33Mhz, the  1X clock  mode is
preferred  for  486  systems  because  it  becomes  increasingly  more
difficult to  build a reliable  system with an oscillator  faster than
66Mhz.

***Versions:...
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*Western Digital...
**WD7855        System controller for 80386SX                <09/25/92
***Notes:...
***Info:
1.3 GENERAL DESCRIPTION

Western  Digital's  WD7855/LV single  chip  ISA  System Controller  is
designed   for  high-performance   IBM  PC/AT   compatible  platforms.
Available for desktop, portable  or low voltage (LV) applications, the
WD7855/LV supports  the 803868X microprocessor operating  at speeds up
to 33 MHz.

The  WD7855/LV incorporates  seven high-performance  system controller
functions which include the ISA bus interface, CPU interface, flexible
memory  controller, DMA controller,  interrupt controller,  timers and
advanced  power  management.  In  combination  with Western  Digital’s
support devices, the WD7855/LV provides a highly flexible and powerful
desktop or portable platform design.

The  WD7855/LV is  designed to  work  with all  variations of  80386SX
compatible microprocessors.  It supports the  traditional dynamic CPUs
with  the industry's  only  Processor Power-down  feature to  minimize
power consumption. The WD7855/LV fully supports static microprocessors
such  as the  AMD  Am386SXL  with CPU  Stop  Clock, System  Management
Interrupt  and  I/O  trapping  features.  The  WD7855/LV  incorporates
special circuitry  which allows  for optimizing the  cache performance
and maintaining  cache coherency  with cached CPUs  such as  the Cyrix
Cx4868LC.

1.3.1 Desktop Applications
The WD7855 provides a high performance solution with a flexible memory
controller architecture, including support  for eight banks of two way
interleave  memory and  EMS  4.0 hardware.   The  WD7855/LV can  fully
support  an external  look-aside cache  or a  combination  primary and
secondary cache.  This feature makes it particularly  suitable for use
with cached microprocessors such  as Cyrix Cx486SLC where it maintains
cache coherency via its built-in bus snooping capability. In addition,
the WD7855/LV  supports Video Local Bus Interface  (VLBI) for enhanced
graphics performance.

1.3.2 Portable Applications
The  WD7855LV  is  an  ideal  choice because  of  its  advanced  power
management features and power saving 3.3 volt operation which delivers
long  battery life in  a compact  footprint. This  makes it  a perfect
choice for laptop, notebook, pen based and palmtop computers.

The eight  bank memory  controller on the  WD7855LV provides  the user
with  great flexibility in  the selection  of 3.3  volt DRAMs  to meet
system  memory requirements  in low  voltage platforms.   The WD7855LV
memory  controller supports JEDEC  standard 3.3  volt DRAM  in various
configurations, including the JEIDA standard 88-pin DRAM card.

The WD7855/LV can be paired  with the appropriate support devices from
Western  Digital  to  deliver  the  most efficient  solution  for  any
platform.  For 5 volt desktop  or portable platforms, the WD7855LV can
be used  with the  WD76C20 Peripheral Controller  and the  WD76C30 I/O
Controller.   Alternatively, the WD7855  can be  used with  the WD7615
Buffer Manager device and a generic  Super I/O chip to implement a low
cost desktop platform. For 3.3  volt applications, the WD7855LV can be
used  with the WD76C20ALV  and WD76C30ALV,  both of  which incorporate
level translators (split rail  operation). For subnotebook and palmtop
type  applications,  WD7625LV  buffer  manager  can be  added  to  the
WD7855LV based solution to achieve a very compact footprint.

The WD7855/LV is a  fourth generation system controller device derived
from  core chips  with  proven compatibility  and  design maturity  in
several  of the  industry’s  leading desktop  and portable  platforms.
Designed with  the state of the  art 0.9 micron  high performance CMOS
process,  the WD7855/LV  family maintains  architectural compatibility
with Western Digital's WD7600 and WD7700 systems logic chip sets while
incorporating many additional performance enhancements.

***Configurations:...
***Features:...
**WD7900/LP/LV  System Chip Set for 80286 or 80386SX (Cache) <11/25/91...
**WD8110        System controller for 80386DX/486            <11/30/93...
**
**Support Chips:
**WD76C20x   Floppy, RTC, IDE and Support Logic Device       <11/25/91...
**WD76C30x   Perip. Ctrl, Interrupt Multiplex, and Clock Gen <11/18/91...
**WD7615     Desktop Buffer Manager                          <04/15/92...
**WD7625     Desktop Buffer Manager                          <10/01/92...
**WD8120LV   Super I/O [no datasheet]                                ?
**Other Chips:...
*Winbond...
*ZyMOS...
*General Sources:...

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