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**82495DX/490DX DX CPU-Cache Chip Set                           <Sep91
***Notes:...
***Info:...
***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):
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**450NX  (?)            06/29/98:...
**?????  (Profusion)    c:99...
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*Headland/G2...
**HT18          80386SX Single Chip                            c:Sep91
***Info:
The HT18  is an advanced PC/AT compatible,  single-chip 80386SX design
solution. This  highly integrated single chip allows  simple, low cost
system  design options  while  featuring high  performance, low  power
consumption,  and minimum board  space requirements.   Advanced memory
management features  include support  for page mode,  with 2  or 4-way
interleaving  in both pipelined  and non-pipelined  modes(18A/B only).
Extended Hardware EMS  options include dual sets of  32 registers with
multiple context operation. Revisions A/B support 256K and 1M DRAMs in
1 by 1,  1 by 4, and 1  by 9 device configurations. Rev  C supports 4M
devices, as well.  A Shadow RAM  option for System Video BIOS and dual
or single system ROM BIOS support adds to overall design versatility.

A  complete PC/AT  compatible  system with  advanced  features may  be
implemented with minimal external support logic. The HT18 performs all
CPU  and peripheral support  functions in  a single  chip.  Integrated
device  functions include  DMA Controllers,  a Memory  Mapper, Timers,
Counters, Interrupt  Controllers, a Bus Controller  and all supporting
circuitry for PC core logic requirements. An asynchronous AT Bus clock
allows  for a  constant 8MHz  Bus clock  rate for  highest  bus device
compatibility as defined in IEEE Spec P996. This device is packaged in
a 208-pin  Plastic Quad Flat  Pack combining several  external buffers
into this space saving solution.

***Configurations:...
***Features:...
**HT21          386SX/286 Single Chip (20 MHz)                 c:Aug91...
**HT22          386SX/286 Single Chip (25 MHz)                 c:Sep91...
**HT25          3-volt Core Logic for 386SX                    c:Dec92...
**HT35          Single-Chip Peripheral Controller [partial info]     ?...
**HTK320        386DX Chip Set                                 c:Sep91...
**HTK340        "Shasta" 486 Chip Set                          c:Jun92...
**Support Chips:
**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.

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