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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
***Notes (Unverified Information!):...
***5600        c:Nov98...
***600         ?...
***620         c:Apr99...
***621         ?...
***630/630E/S  c:Feb00...
***630ST/ET    ?...
***633/633T    c:Mar01...
***635/635T    c:Mar01...
***640T        c:Mar01      ...
**Athlon etc...
*Symphony...
*TI (Texas Instruments)...
*UMC...
*Unresearched:...
*VIA...
*VLSI...
*Western Digital...
**WD76C30x   Perip. Ctrl, Interrupt Multiplex, and Clock Gen <11/18/91
***Notes:...
***Info:
GENERAL
The WD76C30/LV device provides three  functional groups.  It is a Per-
ipheral Controller, Interrupt Multiplexer, and Clock Generator.

The  low power  CMOS  WD76C30/LV  is a  single  device solution  which
provides  interrupt multiplexing logic,  clock generation,  two serial
ports, and one bidirectional parallel port.

Interrupt  multiplexing logic interfaces  the PC/AT  interrupt request
lines with the WD76C10 Single Chip AT Controller.

Integrated clock generation circuitry uses  the 48 MHz input signal to
generate the 1.8462, 3.072, and 8.0 MHz clocks used internally for the
two serial  ports, a 9.6 MHz  Signal used for  the keyboard controller
and  floppy controller,  a programmable  duty/frequency clock  for the
80287 coprocessor, and  a 16 MHz clock for  driving the WD76C10 Single
Chip AT Controller, and floppy controller.

For low power implementations  such as laptops, oscillator disable and
sleep modes are available to power down unused logic.

The bidirectional  parallel port is software configurable  as either a
PC/AT or a PS/2 compatible port. The parallel port data lines and open
drain printer signals have high current drive capabilities.

Each ACE is  programmable as either a WD16C550  or WD16C450 compatible
device. Each WD16C550 configured ACE  is capable of buffering up to 16
bytes  of  data  upon   reception,  relieving  the  CPU  of  interrupt
overhead.  Buffering  of data  also  allows  greater  latency time  in
interrupt servicing which is vital in a multitasking environment. Each
ACE has a maximum recommended data rate of 512 Kbaud.

WD76C30/LV DIFFERENCES
Both the  WD76C30 and WD76C30LV  operate with two power  supplies. The
WD76C30 logic  is powered  by a 5.0  volt supply, while  the WD76C30LV
logic is powered  by a 3.3 volt supply.  The  parallel and serial port
interfaces are only supported by the WD76C30.

PERIPHERAL CONTROLLER
The peripheral controller is  functionally equivalent to the WD16C452/
552. The  mode of operation of  the serial ports and  parallel port is
selectable  via  the  Mode  Select  Register.   Each  serial  port  is
configurable as either a FIFO  enhanced ACE (WD16C550 compatible) or a
standard ACE (WD16C450). The parallel port is configurable as either a
PS/2 bidirectional parallel port  or a PC/AT compatible parallel port.
A detailed description of the  Mode Selection Register is described in
the parallel port section.

***Versions:...
***Features:...
**WD7615     Desktop Buffer Manager                          <04/15/92...
**WD7625     Desktop Buffer Manager                          <10/01/92...
**WD8120LV   Super I/O [no datasheet]                                ?
**Other Chips:...
*Winbond...
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