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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...
**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.

***Versions:...
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*Unresearched:...
*VIA...
**VT82C570M    Apollo Master, Green Pentium/P54C             <06/22/95
***Info:
The VT82C570M Apollo Master  is a high performance, cost-effective and
energy efficient  chip set for  the implementation of  PCI/ISA desktop
and   notebook  personal   computer  systems   based  on   the  64-bit
P54C/Pentium/K5/M1 super-scalar processors. Either  3.3v or 5v CPU and
cache interface is supported up  to 66Mhz CPU external bus speed (with
CPU internal speed up to 150Mhz  and above). In either case, DRAM, PCI
and ISA bus runs at 5v voltage level.

The VT82C570M  chip set consists  of the VT82C575M  system controller,
the  VT82C576M   PCI  bus  controller  with   integrated  master  mode
Enhanced-IDE  controller,  and two  instances  of  the VT82C577M  data
buffers. The CPU bus is  minimally loaded with only the CPU, secondary
cache and the chip set. The VT82C577M data buffers isolate the CPU bus
from the DRAM, PCI and ISA bus so that CPU and cache operation may run
reliably at the high  frequencies demanded by today's processors.  The
chip set  also interfaces directly with the  VT82C416 integrated clock
generator, real time clock with  extended CMOS (128 byte) and keyboard
controller  with PS2  mouse  support.  A complete  main  board can  be
implemented  with only  ten TTLs.  Please refer  to Figure  1  for the
system block diagram.

The  VT82C570M supports eight  banks of  DRAMs up  to 512MB.  The DRAM
controller  supports  Standard  Page  Mode DRAM,  EDO-DRAM  and  Burst
EDO-DRAM in  a flexible mixed/match  manner.  The eight banks  of DRAM
are   grouped  into   four  pairs   with  an   arbitrary   mixture  of
256K/512K/1M/2M/4M/8M/16MxN  DRAMs. Zero,  one  or both  banks may  be
populated in each pair with either 32bit or 64bit data width.

The secondary (L2)  cache is based on Burst  Synchronous (Pipelined or
non-pipelined) SRAM,  asynchronous SRAM or cache module  from 128KB to
2MB. For burst  synchronous SRAMs, 3-1-1-1 timing can  be achieved for
both read and write transactions at 66Mhz. For standard SRAMs, 3-2-2-2
and  4-2-2-2 timing  can be  achieved for  interleaved read  and write
transactions at 66Mhz. Four levels  of CPU/cache to DRAM write buffers
with concurrent  write-back capability  are included in  the VT82C577M
data  buffer  chips  to  speed  up  the  cache  read  and  write  miss
cycles. For primary  cache fill cycles that result  in secondary cache
misses, the primary and secondary caches are filled up concurrently to
further enhance the performance.

***Configurations:...
***Features:...
**VT82C580VP   Apollo VP,  Pentium/M1/K5 PCI/ISA System      <02/15/96...
**VT82C580VPX  Apollo VPX, VPX/97, Pentium with 66/75MHz Bus <01/09/97...
**VT82C590     Apollo VP2, VP2/97, Single-Chip Pentium 66MHz <01/10/97...
**VT82C597/AT  Apollo VP3, Single-Chip for Pentium with AGP  <10/03/97...
**VT82C598MVP  Apollo MVP3,Single-Chip 66/75/83/100MHz & AGP <09/22/97...
**VT8501       Apollo MVP4,Single-Chip 66-100MHz & AGP       <11/04/98...
**VT82C680     Apollo P6, Pentium-Pro Chip Set               <08/30/96...
**Support chips:
**VT82C505     Pentium/486 VL to PCI Bridge                  <05/30/94...
**VT82C586/A/B PCI Integrated Peripheral Controller          <10/13/96...
**VT82C596/A   Mobile PCI Integrated Peripheral Controller   <11/05/97...
**VT82C686A/B  PCI Super-I/O Integrated Peripheral Ctrl.     <02/10/98...
**Later P-Pro/II/III/Celeron...
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