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Digital Electronics: Principles, Devices and Applications

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556 <strong>Digital</strong> <strong>Electronics</strong>64-bit interunit transfer bus32-bit Data BusClockMultiplierBarrelShifterRegisterfileALUFloatingPointUnitFloatingPointRegisterFile32-bit Data BusBase/IndexBus32SegmentationUnitDescriptorRegistersLimit <strong>and</strong>Attribute PLAMicroinstructionControl <strong>and</strong>ProtectionTest UnitControlROMDecodedInstructionPath32Linear Address BusPagingUnitTranslationBufferDisplacement busInstructionDecodePCO, PWT220PhysicalAddress3224CodestreamCacheUnit8k-byteCache128Prefetcher32 byteCodeQueue2x16 bytes323232BusInterfaceAddressDriversWriteBuffers (4x32)Data BusTransceiversBus ControlRequestSequencerBurst BusControlBus SizeControlCacheControlParity generation<strong>and</strong> controlBoundary scancontrolA2-A31,BE0#-BE3#D0-D31ADS#,W/R#,D/C#, M/IO#,PCD,PWT,RDY#,LOCK#,PLOCK#, BOFF#, A20M#,BREQ,HOLD, HLDA, RESET, SRESET,INTR,NMI,FERR#,IGNNE#, STPCLK#BRDY#,BLAST#BS16#-Bs8#KEN#,FLUSH#,AHOLD,EADS#PCHK#,DP0-DP3TCK, TD1,TD0, TMSFigure 13.19Internal architecture of 80486DX.13.11.4.1 80486DX instruction setThe instruction set can be divided into 11 categories including data transfer operations, arithmeticoperations, shift/rotate instructions, bit manipulation instructions, string manipulation instructions,control transfer instructions, high-level language support instructions, operating system supportinstructions, floating point processor control instructions <strong>and</strong> floating-point control instructions13.11.4.2 80486DX registersIt contains all the registers of the 80386 microprocessor <strong>and</strong> 80386 math coprocessor. The register set isdivided into the following categories: base architecture registers, general-purpose registers, instructionpointers, flag registers, segment registers, systems-level registers, control registers, system addressregisters, floating-point registers, data registers, tag word, status word, instruction <strong>and</strong> data pointers<strong>and</strong> control word <strong>and</strong> debug <strong>and</strong> test registers.13.11.4.3 80486DX operating modesThe operating mode of the 80486 processor determines which instructions <strong>and</strong> architectural featuresare accessible. The 80486 has three modes for running programs. These are as follows:1. The protected mode uses the native 32-bit instruction set of the processor. In this mode, allinstructions <strong>and</strong> architectural features are available.

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