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**82395SX     Smart Cache                                     12/17/90
***Notes:...
**82396SX     Smart Cache                                     12/17/90...
**82485       Turbo Cache (and 485Turbocache)                      c90...
**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...
**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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*Headland/G2...
**HT44          Secondary Cache                                c:Jun92
***Info:
The  HT44 is  a  look-aside write-through,  80486SX,  486DX or  486DX2
secondary cache  controller. It is  packaged in an  inexpensive 84-pin
plastic-leaded chip carrier (PLCC).

Architecture
With  its look-aside architecture,  the HT44  fits beside  the CPU-to-
Memory bus  and not in  the data path.   Therefore, once the  HT44 has
been designed  into a  486 system, it  can be populated  for secondary
cache systems or left vacant for non-secondary cache systems. The HT44
is direct-mapped to the available address space.

Performance
The  HT44  has a  number  of  performance  enhancing features.   These
include zero-waitstate burst line fills  to the 486 on secondary cache
hits, and simultaneous 486 and secondary cache updates on read misses.

Memory Configurations
The HT44 supports  cache sizes from 32KBytes to  1MB. Both synchronous
and asynchronous  SRAMs are supported.  25ns SRAMs are  sufficient for
zero-wait-state operation at 33MHz.

Chip Set Support
The HT44 can,  be implemented with minimal glue logic  in a 486 system
with the  HTK340 (code  name Shasta) chip  set.  The registers  in the
HTK340  allow  for programming  of  non-cacheable and  write-protected
areas of  memory. The  HTK340 will support  the HT44  with synchronous
SRAMs only.   Future Headland chip sets will  support both synchronous
and asynchronous SRAM designs.

The HT44  can also be used  with some third-party  chip sets, however,
additional glue logic may be required.

***Versions:...
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*OPTi...
**82C822         PCIB (VLB-to-PCI bridge)                         c:94
***Notes:...
***Info:
OPTi's  82C822 VESA  local bus  to PCI  Bridge (PCIB)  chip is  a high
integration  208-pin PQFP  device designed  to work  with VESA  VL bus
compatible core logic chipsets.  The 82C822 PCIB provides interface to
the high performance PCI bus and is fully compliant to the PCI Version
2.0 specification. The 82C822 requires  no glue logic to implement the
PCI  bus interface  and hence  it allows  designers to  have  a highly
integrated  motherboard with  both VESA  local bus  and PCI  local bus
support. The PCIB chip  offers premium performance and flexibility for
VESA VL-based desktop systems running up to 50MHz. The 82C822 PCIB can
be used with  OPTi's 82C802G core logic and  82C602 buffer chipsets to
build a  low cost and  power efficient 486-based desktop  solution. It
also works  with OPTi 82C546/547  chipset to build a  high performance
PCI/VL solution based on the Intel P54C processor.

The 82C822 PCIB provides all of the control, address and data paths to
access  the PCI  bus from  the  VESA Local  bus (VL  bus). The  82C822
provides  a  complete  solution  including data  buffering,  latching,
steering, arbitration, DMA and  master functions between the 32-bit VL
bus and the 32-bit PCI bus.

The PCIB works seamlessly with  the motherboard chipset bus arbiter to
handle all requests of the host  CPU and PCI bus masters, DMA masters,
I/O relocation  and refresh. Extensive register and  timer support are
designed into the 82C822 to implement the PCI specification.

The 82C822 is a  true VESA to PCI bridge. It  has the highest priority
on  CPU accesses  after cache  and system  memory. It  generates LDEV#
automatically  and  then  compares  the addresses  with  its  internal
registers to determine whether the current  cycle is a PCI cycle. When
a cycle  is identified  as PCI  cycle, the 82C822  will take  over the
cycle and then return RDY# to the CPU. If not, the 82C822 will give up
the  cycle to  the local  device  or, in  the  case of  an ISA  slave,
generate a  BOFF# cycle to the  CPU. This action will  abort the cycle
and allow the CPU to rerun the cycle.

The 82C822 includes  registers to determine shadow  memory space, hole
locations  and sizes  to allow  the 82C822  to determine  which memory
space should be local and which is located on the ISA bus. Upon access
to memory, the 82C822 can determine whether  or not the cycle is a PCI
access by comparing the cycle with its internal registers.

***Versions:...
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*Winbond...
*ZyMOS...
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