CLD-Clear Direction Flag, Clo | Intel 80286, 80287 guide

THE 80286 INSTRUCTION SET

CLD-Clear Direction Flag

OpcodeInstruction ClocksDescription

FC

CLO

2

Clear direction flag. SI and 01 will increment

FLAGS MODIFIED

Direction = 0

FLAGS UNDEFINED

None

OPERATION

CLD clears the direction flag. No other flags or registers are affected. After CLD is executed, string operations will increment the index registers (SI and/or DI) that they use.

PROTECTED MODE EXCEPTIONS

None

REAL ADDRESS MODE EXCEPTIONS

None

8-29

Image 239

Intel 80286, 80287 manual CLD-Clear Direction Flag, Clo

Contents

Page Order Number Dollars ··PRICEIN Call Toll Free 800 548-4725for phone orders Infef Customer Support 80287 Programmers Reference Manual @INTELCORPORATION Organization of this Manual PrefacePage Table of Contents Extended Instruction SET Real Address Mode Chapter Memory Management and Virtual Addressing Table of Contents 10-5 10-110-3 10-4 80286/80287 Supported Data Types Flag Word Contents Dynamic Segment Relocation and Expansion of Segment Limit Code and Data Segments Assigned to a Privilege Level Reserved Exceptions and Interrupts Inter Introduction to Page Chapter Introduction to Memory Management Advanced FeaturesModes of Operation Protection Mechanisms Task Management Organization of this Book Support for Operating Systems Related Publications Inter Base Architecture Page Memory Organization and Segmentation Chapter Base Architecture 8000 r Bytes and Words in Memory Ascii ·3 /80287 Supported Data Types Base Architecture Base Architecture General Registers Registers Memory Segmentation and Segment Registers Index, Pointer, and Base Registers Real Address Mode Segment Selector Interpretation Inlel Inter Stack Operation BP Usage as a Stack Frame Base Pointer Implied Segment Usage by Index, Pointer, and Base Registers Status and Control Registers 10. Flags Register Operands Addressing Modes Memory Addressing Modes Register and Immediate Modes Segment Selection Offset Computation EASE Architecture Segment Register Selection Rules PRog~~~D BX, 51 INPUT/OUTPUTMemory Operand AddressingModes 13. Complex Addressing Modes OUT FF,AL OUTAL,FE Interrupts and Exceptions Hierarchy of Instruction Sets Interrupt Vector Assignments Real Address Mode 80186~80188 Page Basic Instruction Set Page General-Purpose Data Movement Instructions Data Movement Instructions Push Stack Manipulation Instructions Basic Instruction SET Hm====i Flag Operation with the Basic Instruction SETStatus Flags Control Flags Previous Push Instructions LOW Address After Before Popa Arithmetic Instructions Basic Instruction SET Subtraction Instructions Addition Instructions Multiplication Instructions Boolean Operation Instructions Division InstructionsLogical Instructions Wordoprnd Shift and Rotate Instructions ~-i 01, I, I aI a1,1, I, I, I a1,1,1, I aI alaiI 10 01, ,1,101, 0101,1, 01 0 10 I 1I 1I 0 1I 1 1I o I o I 1 o I 1I 1111010rrG Ll 1 1 1 l 1 Control Transfer Instructions Type Conversion and No-Operation InstructionsTest and Compare Instructions Unconditional Transfer Instructions Call Instruction Conditional Transfer Instructions JLE/JNG JG/JNLEJGE/JNL JL/JNGE Software-Generated Interrupts String Manipulation Instructions and Repeat Prefixes Character Translation and String InstructionsTranslate Instruction String Movement Instructions Address Manipulation Instructions Flag Control Instructions Intel Flag Transfer Instructions BINARY-CODED Decimal Arithmetic Instructions Packed BCD Adjustment InstructionsUnpacked BCD Adjustment Instructions Machine State Instructions Trusted InstructionsTrusted and Privileged Restrictions on Popf and Iret Processor Extension Instructions Input and Output Instructions Numeric Data Processor Instructions Processor Extension Synchronization Instructions Basic Instruction SET Data Transfer Instructions Page Extended Instruction Set Page Block 1/0 Instructions Chapter Extended Instruction SET HIGH-LEVEL Instructions Formal Definition of the Enter Instruction Extended Instruction SET Variable Access in Nested Procedures 2b. Stack Frame for Procedure a 2d. Stack Frame for Procedure C at Level 3 Called from B Extended Instruction SET Page Real Address Mode Page Addressing and Segmentation Chapter Real Address Mode Real Address Mode Overlapping Segments to Save Physical Memory Real Address Mode Intr Interrupt PrioritiesNMI Reserved and Dedicated Interrupt Vectors Interrupt Procedures ESC MSW Fffoh Processor State after ResetSystem Initialization Flags Real Address Mode ·Memory Management Virtual Addressing Page Memory Management Overview Chapter Memory Management and Virtual Addressing Format of the Segment Selector Component Virtual Addresses Address Spaces and Task Isolation Descriptor Tables PiDPll~1 VIRTUAL-TO-PHYSICAL Address Translation PIDPLI~1 LOT Descriptor Segments and Segment Descriptors Virtual-to-Physical Address Translation Segment Address Translation Registers Memory Management Registers ~,m~ =--=--=1~~ System Address Registers Memory Management and Virtual Addressing Page Protection7 Page Chapter Protection Protection Implementation Addressing Segments of a Module within a Task Descriptor Cache Registers Protection Separation of Address Spaces LOT and GOT Access Checks LJol LIT Privilege Levels and Protection Example of Using Four Privilege Levels Privilege Usage Segment Descriptor ~~~/do I I LJ. ITI~~ DPL Data Accesses Data Access Restriction by Privilege Level Code Segment Access Pointer Privilege Stamping via Arpl NTE R Control Transfers Gates 10. Gate Descriptor Format Call Gates Se!eC!0r j ,,It Niiii INTRA-LEVEL Transfers VIA Call GateCall Gate Checks INTER-LEVEL Control Transfer VIA Call Gates Protection Stack Changes Caused by Call Gates 12. Stack Contents after an Inter-Level Call Inter-Level Return Checks Tasks and State Transitions Page Task State Segments and Descriptors Introduction Task State Segment and TSS Registers Tasks and State Transitions Task State Segment Descriptors I01 Task Switching Tasks and State Transitions Checks Made during a Task Switch CALL/INT Iret Task Linking Task Gate Descriptor Task Gates ~ASK Page Interrupts and Exceptions Page Interrupt Descriptor Table Definition Interrupt Descriptor Table An eve.! eXtern8~.~~t~~pr~~~~~1 Hardware Initiated Interrupts Interrupt Gates and Trap Gates Software Initiated Interrupts Trap/Interrupt Gate Descriptors SSFROMTSS--~.~r~------~l Trap and Interrupt Gate Checks Interrupts and Exceptions Interrupt and Gate Interactions Infer Deciding Between Task, Trap, and Interrupt Gates Scheduling Considerations Protection Exceptions and Reserved Vectors Processor Extension Segment Overrun Interrupt Double Fault InterruptInvalid OP-Code Interrupt Not Present Interrupt Invalid Task State Segment Interrupt Conditions That Invalidate the TSS Stack Fault Interrupt Additional Exceptions and Interrupts General Protection Fault Interrupt IDT Single Step Interrupt Interrupt System Control Initialization Page Descriptor Table Registers.· Chapter System Control and Initialization Local and Global Descriptor Table Definition System Control and Initialization System Control Instructions MSW Bit Functions Machine Status Word IfTS=1 ESCWait 03FFH Initialization Real Address Mode 10-8 Advanced Topics Page Conforming Code Segments Virtual Memory ManagementSpecial Segment Attributes Expand-Down Segment Expand-Down Data Segments Dynamic Segment Relocation and Expansion of Segment limit Pointer Validation Descriptor Validation Pointer Integrity RPL and the Trojan Horse Problem Multiprocessor Considerations NPX Context Switching Advanced Topics Example of NPX Context Switching Shutdown Page Appendix System Initialization Page Appendix a System Initialization System Initialization System .INITIALIZATION System Initialization Ax,.x Intel· Mov!w MovSiW AX,cl Page Appendix 80286 Instruction Set Page Appendix B 80286 Instruction SET Figure B-1. In Instruction Byte Format 80286 Instruction SET BX + D8 SI + Rb = Rw =REG = Mod=OO Mod=01 Mod=10 Mod=11 Figure B-2 Ir Instruction Byte Format 80286 U\lSTRUCTION SET Instruction Flags Modified ClocksDescription Flags Undefined Protected Mode ExceptionsReal Address Mode Exceptions Error Codes #MP #UD#NM #DF #MP 9 Math Unit Protection Fault No Error Code #GP 13 General Protection Selector or Zero Error Code#MF 16 Math Fault No Error Code #NP 11 Not Present Selector Error Code #NM 7 No Math Unit Available No Error Code #TS 10 Invalid Task State Segment Selector Error Code #SS 12 Stack Fault Selector or Zero Error Code Switchtasks #UD 6 Undefined Opcode No Error CodePrivilege Level and Task Switching on 80286 Instruction SET 80286 Instruction SET AAA Ascii Adjust AL After Addition AAO AAD Ascii Adjust AX Before Division AAM D4 OA AAS AAS-ASCII Adjust AL After Subtraction ADD ADC/ ADD-Integer AdditionADC AND-Logical ARPL- Adjust RPL Field of Selector Bound rw,md noj=13 BOUND-Check Array Index Against Bounds Call Flags ModifiedFlags Undefined Operation Call to Call Gate Call FARCall Conforming Code Segment Call Nonconforming Code Segment Call Task Gate Protected Mode Exceptions80286 Instruction SET Call Gate to More Privilege Call Gate to Same Privilege Interrupt l3 for a word operand at offset Offffh C8W Caw-Convert Byte into Word CLC CLC-Clear Carry Flag CLO CLD-Clear Direction Flag 80286·INSTRUCTION SET Protected Mode ExceptionsReal Address Mode Exceptions Ell-Clear Interrupt Flag Opcode Instruction ClocksDescription CLTS-Clear Task Switched Flag CMC CMC-Complement Carry Flag CMP CMP-Compare Two Operands Cmpsw CMPS8 CWD CWO-Convert Word to Doubleword DAA DAA-Decimal Adjust AL After Addition DAS-Decimal Adjust AL After Subtraction Opcode Structlon Clocks Description DEC-Decrement by DIVew DIV -Unsigned DivideDIVeb BP= Frameptr ENTER-Make Stack Frame for Procedure Parameters 80286 Instruction SET Protected Mode Exceptions HLT-Halt IDIV-Signed Divide 21,mem=24 Signed multiply rw = EA word X imm. byte IMUL-Signed MultiplyOpcode Instruction Clocks Description Imul eb 21,mem=24 Signed multiply rw = IN-Input from Port Mem=7 Increment EA word by INC Insw INS/INSB/INSW-Input from Port to StringINS Insb INT3 INT IINTO-Call to Interrupt Procedure Interrupt to Same Privilege Level InterruptInterrupt to Inner Privilege #GP, #NP, #SS, and #TS, as indicated in the list above Interrupt Return IRET-Interrupt ReturnOpcode Instruction Clock Description Iret Interrupt Return to Same Level Interrupt Return on Stack #GP, #NP, or #88, as indicated in the above listing JLE JAEJBE JGE 80286 Instruction SET JMP-Jump Jump to Call Gate Jump FARJump Conforming Code Segment Jump Nonconforming Code Segment Jump Task State Segment Lahf LAHF-load Flags into AH Register 02 Ir 14,mem=16 Load highrw= Access Rights byte, selector ewReal Address Mode Exception Instruction SET LES LOS/ LES-Load Doubleword PointerLDS 80286 Instruction SET Protected Mode Exceptions Effective Address Offset LEA-load Leave LEAVE-HighLevel Procedure Exit LlDT LGDTILIDT-Load Global/Interrupt Descriptor Table RegisterLgdt Load m into Global Descriptor Table reg Register LLDT-Load Local Descriptor Table RegisterLldt ew Load selector ew into Local Descriptor Table 01 /6 LMSWew Mem=6 LMSW-Load Machine Status Word Lock LOCK-AssertBUS Lock Signal Lodsw LodsLODS8 LOOP/LOOPcond-Loop Control with CX Counter 14,mem=16 Load rw = Segment Limit, selector ew LSL-LoadSegment Limit 00 /3 LTR ew 17,mem=19 LTR-Load Task Register Mem=5 Move EA byte into byte register Opcode Instruction Clocks DescriptionMem=3 Move byte register into EA byte Mem=3 Move word register into EA word Interrupt 13 for a word operand at offset Offffh Movsw MOVS/MOVSB/MOVSW-Move Data from String to StringMovs MOVS8 MUL-Unsigned Multiplication of AL or AX NEG ew NEG-TwosComplement NegationNEG eb NOP-No Operation Not NOT-OnesComplement Negation OR- Logical Inclusive or Output word AX to port number OX OUT OX,ALOutput byte AL to port number OX OUT OX,AX Outsw OutsOutsb POP SS POP Inter Popa FlAGS Undefined Popf POPF-Pop from Stack into the Flags Register Push SS PUSH-Push a Word onto the StackPush Push CS PUSHA-Push All General Registers Pushf PUSHF-Push Flags Register onto the StackPush flag~ register ROR RCLRCR ROL Interrupt 13 for a word operand at offset Offffh REP Movs REP INSREP Insb REP Insw 80286 Instruction SET RET RET -Return from Procedure Return to Outer Privilege Level Return to Same Level Sahf Sahf -Store AH into Flags SHR SALSAR Interrupt 13 for a word operand at offset Offffh SBB SBB-Integer Subtraction With Borrow SCAS/SCASB/SCASW-Compare String Data 101 Sgdt /SIDT-Store Global/Interrupt Descriptor Table Register SLOT-Store Local Descriptor Table Register 103 Smsw -Store Machine Status Word 104 STe-SetCarry Flag STO STOSetDirection Flag STI STI-Set Interrupt Enable Flag Stosw Stoss 108 STR-Store Task Register00 /1 STR ew Mem=3 SUB SUB-Integer Subtraction Test TEST-Logical Compare 111 VERR,VERW-Verifya Segment for Reading or Writing14,mem=16 Set ZF=1 if seg. can be read, selector ew 14,mem=16 112 Wait WAIT-Wait Until Busy Pin Is Inactive High Xchg XCHG- Exchange Memory/Register with Register 115 Xlat -Table Look-up TranslationXlat mb Set AL to memory byte Osbx + unsigned Xlatb XOR XOR-Logical Exclusive or Appendix 8086/8088 Compatibility Considerations Page Table C-1. New 80286 Interrupts Software Compatibility Considerations Pushbp MOVBP,SP XCHGBP,BP Hardware Compatibility Considerations Page 80286/80386 Software Page 80286/80386 Softvvare 80286/80386 Software Compatibility Considerations Index-1 Index Index-2 Index-3 Index-4 LODS/LODSB/LODSW, 3-24, B-69 Index-5 Index-6 Numeric Processor Extension NPX Page 80286 Microsystem AN Introduction to Related Publications Organization of This Manual Unnormals-Descendents of Denormal Operands Chapter Overview of Numeric Processing Chapter SYSTEM-LEVEL Numeric Programming 80287 Glossary of 80287 and FLOATING-POINT Terminology Index Storage Allocation Directives Tables Overview of Numeric Processing Page Performance Introduction to the 80287 Numeric Processor Extension Fxam StackO assumed Examine Overview of Numeric Processing ± Vb2 4ac Applications Upgradability PASCAL-286 FORTRAN-286 Programming Interface Numeric Data Types Hardware Interface ~r=~=~ NPX Register Stack Numeric Processor Architecture 80287 Register Set NPX Status Word Status Word Control Word Infinity, positive Inter Tag Word Format Number System Computation Fundamentals Number System Data Types and Formats Data Formats Binary Integers Rounding Control ·6. Rounding Modes Precision Control Special Numeric Values Special Computational Situations Nonnormal Real Numbers Overview of Numeric Processing Denormalization Process Unnormals-Descendents of Denormal Operands FLD FrndintFsqrt FIST, FISTP, Fbstp Infinity Fsqrt FLD, FBLD1 FILD2 FST,FSTPFbstp FIST, Fistp Fprem +co Ftst FrndintFxtract ......1 ---- 15 bits-----l..~1 LargestSmallest Zero Smallest U U ZeroU U2 Bits Normals Class NaNs16. Temporary Real Encodings Sign Biased Exponent Significand· Zero Divisor 16. Temporary Real Encodings ContdInvalid Operation Overview of Numeric Processing Denormalized Operand 17. Exception Conditions and Masked Responses Masked response to overflow exception earlier 17. Exception Conditions and Masked Responses Contd 11. Arithmetic Example Using Infinity Software Exception Handling Programming Numeric Applications Page Numeric Operands 80287 NPX Instruction SETCompatibility with the 8087 NPX Data Transfer Instructions FAD D destination, source Programming Numeric Applications Arithmetic Instructions Arithmetic Instructions Fdiv Azimuth FaddFsub Fmulp Fsubrp / /destination/source Fprem Condition Code Interpretation after Fprem Condition Code Interpretation after Fcom Programming Numeric Applications FabsFcom / /source Comparison Instructions Fxam Fcompp STO 1r Fptan FYL2XP1 FpatanF2XM1 FYL2X Constant Instructions Processor Control Instructions Finitifninit Fstsw AX/FNSTSW AX FSAVE/FRSTOR Memory Layout Fstenvifldenv Memory Layout Ffree destination Instruction Execution Time 12. Key to Operand TypesProgramming Numeric Applications 13. Execution Penalties Instruction Length ·14. Instruction Set Reference Data 14. Instruction Set Reference Data Contd Fdivr Programming Numeric Applications FdecstpFdiv Fdivp Ficom BP+4.PARMCOUNT Ffree ST1Fiadd DISTANCE..TRAVELLED Fiadd Pulsecount SI Ficom TOOL.NPASSES Fimul Bearing Fidivr FrequencyFild Standoff DI Fild RESPONSE.COUNT Fistp Correctedtime Fist OBS.COUNTSIFist BP.FACTOREDPULSES Fistp BX.ALPHACOUNT SI FLDLG2 FLD Reading 81.PRE88UREFLO 8AVEREADING Fldcw Controlword Floz FLOL2EFLOL2T Flopi Fpatan Fmul SpeedfactorFmulp ST1,ST Fsave BP ·14. Instruction Set Reference Data ContdFptan Frstor BP Fstcw Savecontrol FST ST3FST Correlation FST Meanreading Fstp Regsave SI Fstp BX.ADJUSTEDRPMFstp ST2 Fstp Totaldosage Fsubrp ST1,ST Fsubr ST,ST1Fsubr Vectorsi Fsubr BX.INDEX FYL2XP1 Fxch ST2FYL2X High-Level Languages Programming Facilities 15. PLlM-286 Built-In Procedures Interpretation Data Types ASM286 BIT String Shorti Nteger OFFFFFF82H HEX Must Start Status Word Record Definition TR E Q Filo BP.BETA 17. Addressing Mode ExamplesFiaooalpha FOIVRALPHA.BETA Fsub Alpha SI Sample PL/M-286 Program It *it Concurrent Processing with Emulation ·7. Sample ASM286 Program Intel Programming Numeric Applications Sample ASM286 Program Contd Instruction Synchronization Managing Concurrency Data Synchronization Synchronizing References to Shared Data Error Synchronization MOV Fsgrt System-Level Numeric Programming Page Processor Extension Data Channel Real-Address Mode and Protected Virtual-Address ModeArchitecture Recognizing. the 80287 NPX Dedicated and Reserved 1/0 LocationsProcessor Initialization and Control System Initialization Software Routine to Recognize SYSTEM-LEVEL Numeric Programming Configuring the Numerics Environment NPX Processor State Following Initialization Initializing Handling Numeric Processing Exceptions Inter Simultaneous Exception Response Precedence of NPX Exceptions Numeric Programming Examples Page Chapter Numeric Programming Examples XAM Jump Table for Examine Routine Conditional Branching for Fxam Contd Numeric Programming Examples Proc MOV Byte PTR IBP-121, OH Fldenv Fnsave BP-941 FLOATING-POINT to Ascii Conversion Examples It116 Ebde DoeF \ii.t 4BB Lei Function. Partitioning Description of Operation Exception ConsiderationsSpecial Instructions Scaling the Value Trigonometric Calculation Examples Output Format Numeric Programming Examples Calculating Trigonometric Functions 207 Arg 0o,3 Coce 4676 Page Machine Instruction Encoding and Decoding Page REG OP-A MOD OP-S Displacement Format OP-AMOD Table A·2. Machine Instruction Decodin.9 Guide Machine Instruction Encoding and Decoding MOD10 Machine Instruction Encoding and DecodingModoo MOD01 Table A-2. Machine Instruction Decoding Guide Contd XXX 1REGOreg FstswaxPage Appendix Compatibility Between NPX Page 80287 NPX Appendix B Compatibility Between NI NIT Appendixc· Page Appendix C Implementing the Ieee P754 Standard Additional Software to Meet the Standard Implementing the Ieee P754 Standard Page Glossary of 80287 and Floating-Point Terminology Page Glossary-1 Glossary FLOATING-POINT Terminology Inter Glossary of 80287 and FLOATING-POINT Terminology Glossary-3 Glossary of 80287 and FLOATING-POINT Terminology Glossary-4 Glossary of 80287 and FLOATING-POINT Terminology Page Index Index-2 NO-WAIT Form Index-4 Inter Inter IntJ European Sales Offices