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**82495DX/490DX DX CPU-Cache Chip Set                           <Sep91
***Notes:...
***Info:...
***Configurations:...
***Features:
o   50 MHz Intel486 DX CPU 
    - RISC Integer Core with Frequent Instructions Executing in One 
      Clock
    - 160 Mbyte/Sec Burst Bus
    - 41 Dhrystone MIPs
    - 11.5M Double Precision Whetstones/Sec.
    - On-Chip Cache and FPU
o   Highly Flexible
    - Supports 128 Kbyte and 256 Kbyte Configurations
    - Complete MESI Protocol Support
    - 32- or 64-Bit Memory Bus Width
    - Synchronous, Asynchronous, and Strobed Memory Bus Protocols
    - Variable Cache Line Sizes and Sectoring
    - Cache Data Parity Option
o   High Performance Second Level Cache
    - Two-Way Set Associative
    - Write-Back or Write Through Cache
    - Zero Wait State Cache Access
    - Concurrent CPU Bus, Memory Bus, and Internal Array Operation
o   Full Multiprocessing Support
    - Implements MESI Write-Back Cache Protocol
    - Low Bus Utilization
    - Automatically Maintains 1st Level Cache Consistency
    - Supports Read-for-Ownership, Write-Allocation, and Cache-to-
      Cache Transfers

**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...
**800 series...
*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.

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**UM82c45x     Serial/Parallel chips                                 ?
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