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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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**5571           (Trinity) Pentium PCI/ISA Chipset (75MHz)   <12/09/96
***Info:
[no general section in datasheet]

3. Functional Description
3.1 DRAM Controller
3.1.1 DRAM Type
The SiS5571  can support up to  384MBytes (3 banks) of  DRAMs and each
bank could be single or double sided 64 bits FP (Fast Page mode) DRAM,
EDO  (Extended  Data  Output)   DRAM,  and  SDRAM  (Synchronous  DRAM)
DRAM. Half populated bank(32-bit) is also supported.

The installed DRAM type can be 256K,  512k, 1M, 2M, 4M or 16M bit deep
by n bit  wide DRAMs, and both symmetrical  and asymmetrical type DRAM
are supported. It is also  permissible to mix the DRAMs (FP/EDO/SDRAM)
bank  by bank  and  the  corresponding DRAM  timing  will be  switched
automatically according to register settings.

3.1.2 DRAM Configuration

The SiS5571 can support single  sided or double sided DRAM modules for
each bank. The basic configurations are shown as the following:

3.1.3 Double-sided DRAM    [omitted see datasheet]
3.1.4 Single-sided DRAM    [omitted see datasheet]
3.1.5 DRAM Scramble Table  [omitted see datasheet]
3.1.6 64-bit mapping table [omitted see datasheet]

3.2 DRAM Performance       [omitted see datasheet]

3.3 CPU to DRAM Posted Write FIFOs

There is  a built-in CPU  to Memory posted  write buffer with  8 QWord
deep ( CTMFF). All the write  access to DRAM will be buffered. For the
CPU read miss / Line fill cycles, the write- back data from the second
level cache will be buffered first,  and right after the data had been
posted write into the FIFO, CPU can performs the read operation by the
memory controller starting to read  data from DRAMs. The buffered data
are  then written  to DRAM  whenever no  any other  read  DRAM request
comes. With  this concurrent write  back policy, many wait  states are
eliminated. If  there comes a  bunch of continuous DRAM  write cycles,
some ones will be pending if the CTMFF is full.

3.4 32-bit (Half-Populated) DRAM Access
For the read  access, there will be either single  or burst read cycle
to access the DRAM which depends  on the cacheability of the cycle. If
the  current  DRAM  configuration  is half-populated  bank,  then  the
SiS5571 will assert 8 consecutive  cycles to access DRAM for the burst
cycle.  For the  single cycle that only accesses  DRAM within a DWord,
the SiS5571 will  only issue one cycle to access  DRAM. For the single
cycle that  accesses one  Qword or cross  DWord boundary,  the SiS5571
will issue two consecutive cycles to access DRAM.

3.5 Arbiter
The arbiter is the interface  between the DRAM controller and the host
which  can  access  DRAMs.  In  addition  to  pass  or  translate  the
information  from   outside  to  DRAM  controller,   arbiter  is  also
responsible for which master has  higher priority to access DRAMs. The
arbiter treats different DRAM access  request as DRAM master, and that
makes there be  5 masters which are trying to  access DRAMs by sending
their request to the arbiter. After one of them get the grant from the
arbiter, it owns DRAM bus and begins to do memory data transaction.

The masters are: CPU read request, PCI master, Posted write FIFO write
request, and Refresh  request. The order of these  masters shown above
also stands for their priority to access memory.

3.6 Refresh cycle
The refresh cycle  will occur every 15.6 us. It is  timed by a counter
of 14Mhz input.  The CAS[7:0]# will be asserted at  the same time, and
the RAS[5:0]# are asserted sequentially.

3.7 PCI bridge
SiS5571 is  able to operate  at both asynchronous and  synchronous PCI
clocks. Synchronous  mode is provided for those  synchronous system to
improve the overall system performance.  While in the PCI master write
cycles, post-write  is always performed.  And function  of Write Merge
with CPU-to-DRAM  post-write buffer  is incorporated to  eliminate the
penalty of snooping write-back. On the other hand, prefetch is enabled
for master read cycles by default, and such function could be disabled
optionally.  And, Direct-Read  from CPU-to-DRAM  post-write  buffer is
implemented to eliminate the overhead of snooping write-back also.  In
addition to  Write-Merge and  Direct-Read, Snoop-Ahead also  hides the
overhead of inquiry cycles for master to main memory cycles. These key
functions,  Write-Merge,  Direct-Read  and  Snoop-Ahead,  achieve  the
purpose  of zero  wait for  PCI  burst transfer.   The post-write  and
prefetch buffers are both 16 Double-Word deep FIFOs.

3.8  Snooping Control                          [omitted see datasheet]
3.9  AHOLD/BOFF# Process and Arbiter Interface [omitted see datasheet]
3.10 Target Initiated Termination    	       [omitted see datasheet]
3.11 DATA Flow	      			       [omitted see datasheet]
3.12 PCI Master Read/Write DRAM Cycle	       [omitted see datasheet]


***Configurations:...
***Features:...
**5581/5582      (Jessie)  Pentium PCI/ISA Chipset (75MHz)   <04/15/97...
**5591/5592/5595 (David)   Pentium PCI A.G.P. Chipset        <01/09/98...
**5596/5513      (Genesis) Pentium PCI Chipset               <03/26/96...
**5597/5598      (Jedi)    Pentium PCI/ISA Chipset           <04/15/97...
**530/5595       (Sinbad) Host, PCI, 3D Graphics & Mem. Ctrl.<11/10/98...
**540            (Spartan) Super7 2D/3D Ultra-AGP Single C.S.<11/30/99...
**55x            SoC (System-on-chip)                        <03/14/02...
**
**Support chips:
**85C206     Integrated Peripheral Controller [no datasheet]         ?...
**5595       Pentium PCI System I/O                          <12/24/97...
**950        LPC I/O                                         <07/16/99...
**Other:...
**PII/III/Pro...
**Athlon etc...
*Symphony...
*TI (Texas Instruments)...
*UMC...
*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...
**Later AMD...
**Other...
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