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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:
***440FX (Natoma)       05/06/96...
***440LX (Balboa)       08/27/97...
***440BX (Seattle)      c:Apr'98...
***440DX (?)            c:?...
***440EX (?)            c:Apr'98...
***440GX (Marlinespike) 06/29/98...
***440ZX & 440ZX-66 (?) 01/04/99...
***440ZX-M (?)          05/17/99...
***440MX (Banister)     05/17/99...
**450NX  (?)            06/29/98:...
**?????  (Profusion)    c:99...
**800 series...
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*SIS...
**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...
**VT82C580VPX  Apollo VPX, VPX/97, Pentium with 66/75MHz Bus <01/09/97
***Notes:...
***Info:
The VT82C580VPX  Apollo-VPX is a high  performance, cost-effective and
energy efficient chip set for  implementation of PCI / ISA desktop and
notebook   personal   computer   systems   based   on   64-bit   P54C/
Pentium/K5/K6/M1 super-scalar processors.   The CPU / cache connection
is  supported  using  an  "asynchronous"  interface up  to  75Mhz  CPU
external bus speed  (with CPU internal speed up  to 200Mhz and above),
with  CPUs   such  as  the   "P200+"  processors  from  Cyrix   /  IBM
Microelectronics.  The  "asynchronous" interface allows  the processor
external  bus  frequency  to  be  increased above  66MHz  while  still
allowing the PCI  bus to run at the specified  top frequency of 33MHz.
The  chipset also  supports CPU  external bus  speeds up  to  66MHz in
"synchronous" mode, so may also  be used in boards designed around the
popular VT82C580VP (Apollo VP)  chipset.  The 66MHz external bus speed
is used primarily for Intel and AMD processors.  The CPU, DRAM and PCI
bus are all  independently powered so that each of the  bus can be run
at 3.3v or 5v, independently.  The ISA bus always runs at 5v.

The  VT82C580VPX   chip  set   consists  of  the   VT82C585VPX  system
controller, the VT82C586B PCI to  ISA bridge, and two instances of the
VT82C587VP  data  buffers.   The  VT82C585VPX is  the  only  different
component in  a VPX-based system from  the chips used in  an Apollo VP
system: the same VT82C586B South Bridge  chip may be used with all VIA
North  Bridge chips  (Pentium  and PentiumPro-based  designs) and  the
VT82C587VP  Data Buffer  is the  same  chip as  is used  in Apollo  VP
designs.

The CPU bus is minimally loaded with only the CPU, secondary cache and
the chip  set.  The VT82C587VP data  buffers isolate the  CPU bus from
the DRAM and PCI bus so  that CPU and cache operation may run reliably
at  the   high  frequencies  demanded  by   today's  processors.   The
VT82C585VPX contains multiple deep FIFOs to allow efficient concurrent
operation  and DRAM  utilization.   The VT82C586B  PCI  to ISA  bridge
includes  integrated  206-style  IPC  (DMA, interrupt  controller  and
timer),  integrated  keyboard   controller  with  PS2  mouse  support,
integrated DS12885 style  real time clock with extended  256 byte CMOS
RAM,  ACPI-compatible Power  Management  subsystem, integrated  master
mode enhanced IDE / UltraDMA-33  disk controller with full scatter and
gather capability, and integrated USB (universal serial bus) interface
with  root hub  and two  function ports  with built-in  physical layer
transceivers  (refer   to  the  separate  VT82C586B   Data  Sheet  for
additional  information).  A  complete main  board can  be implemented
with only six TTLs.  Refer to  Figure 1 [see datasheet] for the system
block diagram.
***Configurations:...
***Features:...
**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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