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**82495DX/490DX DX CPU-Cache Chip Set <Sep91
***Notes:...
***Info:
The 50 MHz Intel486 DX CPU-Cache Chip Set provides a high performance
solution for servers and high-end desktop systems. This binary
compatible solution has been optimized to provide 50 MHz, zero wait
state performance. The CPU-Cache chip set combines the 50 MHz Intel486
Microprocessor with the 82495DX/82490DX cache subsystem. It delivers
integer performance of 41 V1.1 Dhrystone MlPs and a SPEC integer
rating of 27.9. The cache subsystem features the 82495DX Cache
Controller and the 82490DX Dual Ported Data RAM. Dual ported buffers
and registers of the 82490DX allow the 82495DX Cache Controller to
concurrently handle CPU bus, memory bus, and internal cache operations
for maximum performance.
The CPU-Cache Chip Set offers many features that are ideal for multi-
processor based systems. The Write-Back feature provides efficient
memory bus utilization by reducing bus traffic through eliminating
unnecessary writes to main memory. The CPU-Cache chip set also
supports MESI protocol and monitors the memory bus to guarantee cache
coherency.
The 50 MHz Intel486 DX CPU and 82495DX/82490DX Cache subsystem are
produced on Intel's latest CHMOS V process which features submicron
technology and triple layer metal.
3.0 ARCHITECTURAL OVERVIEW
3.1 Introduction
The Intel486 CPU-cache chip set provides a tightly coupled processing
engine based on the Intel486 microprocessor and a cache subsystem
comprised of the 82495DX cache controller and multiple 82490DX cache
components. Figure 3.1 [see datasheet] diagrams the basic config-
uration.
The cache subsystem provides a gateway between the CPU and the memory
bus. All CPU accesses that can be serviced locally are transparent to
the memory bus and serve to avoid bus traffic. As a result, the cache
chip set reduces memory bus bandwidth to both increase Intel486
processor performance and support efficient multiprocessor systems.
The cache subsystem also decouples the CPU from the memory bus to
provide zero-wait-state operation at high clock frequencies while
allowing relatively slow and inexpensive memories.
The CPU-cache chip set prevents latency and bandwidth bottlenecks
across a variety of uniprocessor and multiprocessor designs. The
processor’s on-chip cache supports a very wide CPU data bus and
high-speed data movement. The second-level cache greatly extends the
capabilities of the on-chip cache resources, enabling a larger portion
of memory cycles to be satisfied independently of the memory bus.
3.2 CPU-Cache Chip Set Description
The chip set is comprised of three functional blocks:
3.2.1 CPU
The chip set includes a special version of the Intel486DX micropro-
cessor at 50 MHz. The Intel486DX Microprocessor Data Sheet provides
complete component specifications.
3.2.2 CACHE CONTROLLER
The 82495DX cache controller is the main control element for the chip
set. providing tags and line states. and determining cache hits and
misses. The 82495DX executes all CPU bus requests and coordinates all
main memory accesses with the memory bus controller (MBC).
The 82495DX controls the data paths of the 82490DX cache components
for cache hits and misses and furnishes the CPU with needed data. The
controller dynamically adds wait states as needed using the most
recently used (MRU) prediction algorithm.
The 82495DX also performs memory bus snoop operations in shared memory
systems and drives the cycle address and other attributes during
memory bus accesses. Figure 3.2 [see datasheet] diagrams the 82495DX.
3.2.3 CACHE SRAM
Multiple 82490DX cache components provide the cache SRAM and data
path. Each component includes the latches, muxes and logic needed to
work in lock step with the 82495DX to efficiently serve both hit and
miss accesses. The 82490DX components take full advantage of VLSI
silicon flexibility to exceed the capabilities of discrete
implementations. The 82490DX components support zero-wait-state hit
accesses and concurrent CPU and memory bus accesses, and they
replicate MRU bits for autonomous way prediction. During memory bus
cycles. the 82490DX components act as a gateway between CPU and memory
buses. Figure 3.3 [see datasheet] diagrams an 82490DX cache component.
3.3 Secondary Cache Features
The 82495DX cache controller and 82490DX cache components provide a
unified, software transparent secondary data and instruction cache.
The cache enables a highspeed processor core that provides efficient
performance even when paired with a significantly slower memory bus.
The secondary cache interprets CPU bus cycles and can service most
memory read and write cycles without accessing main memory. I/O and
other special cycles are passed directly to the memory bus. The cache
has a dual-port structure that permits concurrent CPU and memory bus
operation.
The 82495DX cache controller contains the 8K tag entries and logic
needed to support a cache as large as 256K. Combinations of between 4
and 9 82490DX cache SRAMs are used to create caches ranging from 128K
to 256K, with or without data parity.
The MBC provides logic needed to interface the CPU, 82495DX and
82490DX to the memory bus. Because the MBC also affects system
performance. its design can be the basis of product differentiation.
***Configurations:...
***Features:...
**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...
*HMC (Hulon Microelectronics)...
*Logicstar...
*Motorola...
*OPTi...
**82C596/597 PTMAWB Pentium Adaptive Write-back (Cobra) c:93
***Notes::...
***Info:...
***Configurations:...
***Features:...
**82C650/1/2 Discovery (Pentium Pro) [no datasheet] ?...
**82C681/2/6/7 386/486WB EISA c:92...
**82C683 386/486AWB EISA [no datasheet] ?...
**82C693/6/7 Pentium uP Write Back Cache EISA c:93...
**82C700 FireStar c:97...
**82C701 FireStar Plus c:97...
**82C750 Vendetta [no datasheet] ?...
**82c801 SCWB2 DX Single Chip Solution c:92...
**82C802 SCWB2 PC/AT Single Chip [no datasheet] ?...
**82C802G/GP System/Power Management Controller (cached) c:93...
**82C895 System/Power Management Controller (cached) c:Sep94...
**82C898 System/Power Management Controller (non-cache)c:Nov94...
**
**Support Chips:
**82C601/2 Buffer Devices <Nov94...
**82C822 PCIB (VLB-to-PCI bridge) c:94...
**Other:...
*PC CHIPS/Amptron/Atrend/ECS/Elpina/etc...
*SIS...
*Symphony...
*TI (Texas Instruments)...
*UMC...
**UM82C*** (IBM/INTEL Direct replacement) c87
Note: Dates vary for when these chips were first available. Two
databooks have been used one from '86 the other from '91. Not all the
chips are listed in the '86 databook, the date of '87 is an
assumption.
PC/XT:
IBM: UMC: Desc:
Intel 8284 UM82C84A 25MHz CMOS Clock Generator and Driver
Intel 8288 UM82C88 Bus Controller
Intel 8259 UM8259A Programmable Interrupt Controller also UM82C59A-2 (CMOS version)
Intel 8237 UM8237A 3-5MHz Programmable DMA Controller (DMAC)
Intel 8253 UM8253*2 2.6-5MHz Programmable Interval Timer
Intel 8255 UM82C55A* Programmable Peripheral Interface
Note: * indicates: possible compatibility, datasheet does not state
explicitly. YMMV.
Note: *2 indicates: The UM8253 can be replaced with the
UM82C54/-2. The datasheet says it is a superset of the 8253, and
works up to 10MHz. Also it's compatible with the 8254. AT: IBM:
UMC: Desc: Intel 82284 UM82C284* 10-12.5MHz Clock Generator and
Ready Interface Intel 82288 UM82C288* 10-12.5MHz Bus Controller
Intel 8254 UM82C54/-2 8-10MHz CMOS Programmable Interval Timer
Intel 8259 UM8259A Programmable Interrupt Controller also
UM82C59A-2 (CMOS version) Intel 8237 UM8237A 3-5MHz Programmable
DMA Controller (DMAC) 74LS612 UM74HCT612* Memory Mapper MC146818
RTC UM82C6818* Real-Time Clock (RTC) Intel 8047 ?? Keyboard
Controller
Note: * indicates: possible compatibility, datasheet does not state
explicitly. YMMV.
**UM82C088 PC/XT Integration Chip <91...
**UM82C230 286AT MORTAR Chip Set <91...
**UM82C210 386SX/286 AT Chip Set <91...
**UM82C3xx Twinstar & UM82C336F/N & UM82C39x [no datasheet] ?...
**UM82C380 386 HEAT PC/AT Chip Set <91...
**UM82C480 386/486 PC Chip Set c91...
**UM82C493/491 ??????????????? [no datasheet] ?...
**UM8498/8496 486 VL Chipset "Super Energy Star Green"[no dsheet]c94...
**UM8881/8886 HB4 PCI Chipset "Super Energy Star Green"[no dsheet]c94...
**UM8890 Pentium chipset [no datasheet] ?...
**
**Support Chips:
**UM82152 Cache Controller (AUStek A38152 clone) <91...
**UM82C852 Multi I/O For XT <91...
**UM82C206 Integrated Peripheral Controller <91...
**UM82c45x Serial/Parallel chips ?...
**Other chips:...
*Unresearched:...
*VIA...
*VLSI...
*Western Digital...
*Winbond...
*ZyMOS...
*General Sources:...
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