Am486DE2 Microprocessor

5

WB/WT (New) ...................................................................................................................................... 16

W/R ...................................................................................................................................................... 16

Functional Description................................................................................................................................ 17

Overview .............................................................................................................................................. 17

Memory ................................................................................................................................................ 17

Modes of Operation ............................................................................................................................. 17

Write-Through Cache Architecture ...................................................................................................... 17

Cache Replacement Description ......................................................................................................... 17

Memory Configuration ......................................................................................................................... 17

Clock Control.............................................................................................................................................. 18

Clock Generation ................................................................................................................................. 18

Stop Clock ........................................................................................................................................... 18

Stop Grant Bus Cycle .......................................................................................................................... 19

Pin State During Stop Grant ................................................................................................................ 19

Clock Control State Diagram ............................................................................................................... 20

SRESET Function ...................................................................................................................................... 20

System Management Mode ....................................................................................................................... 22

Overview .............................................................................................................................................. 22

Terminology ......................................................................................................................................... 22

System Management Interrupt Processing.......................................................................................... 22

Entering System Management Mode .................................................................................................. 26

Exiting System Management Mode ..................................................................................................... 27

Processor Environment ....................................................................................................................... 27

Executing System Management Mode Handler .................................................................................. 28

SMM System Design Considerations .................................................................................................. 31

SMM Software Considerations ............................................................................................................ 34

Test Registers 4 and 5 Modifications ......................................................................................................... 36

TR4 Definition ...................................................................................................................................... 36

TR5 Definition ...................................................................................................................................... 36

Am486DE2 Microprocessor Functional Differences................................................................................... 37

Am486DE2 Microprocessor Identification .................................................................................................. 37

DX Register at RESET ........................................................................................................................ 37

CPUID Instruction ................................................................................................................................ 37

Electrical Data ............................................................................................................................................ 39

Power Connections.............................................................................................................................. 39

Power Decoupling Recommendations................................................................................................. 39

Other Connection Recommendations.................................................................................................. 39

Absolute Maximum Ratings........................................................................................................................ 40

Operating Ranges ...................................................................................................................................... 40

DC Characteristics over Commercial Operating Ranges ........................................................................... 40

Switching Characteristics over Commercial Operating Ranges................................................................. 41

Switching Characteristics for 33-MHz Bus (66-MHz Microprocessor) ................................................. 42

Switching Waveforms .......................................................................................................................... 43

Package Thermal Specifications ................................................................................................................ 48

Physical Dimensions .................................................................................................................................. 50

168-Pin PGA ........................................................................................................................................ 50

208-Lead SQFP ................................................................................................................................... 51