@Assembler Programming Topics :asm:8086 architecture ^Intel 8086 Family Architecture %General Purpose Registers Segment Registers AX AH/AL (EAX) Accumulator CS Code Segment BX BH/BL (EBX) Base DS Data Segment CX CH/CL (ECX) Counter SS Stack Segment DX DH/DL (EDX) Data ES Extra Segment (FS) 386 only (reg) indicates 386 (GS) 386 only %Pointer Registers Stack Registers SI (ESI) Source Index SP (ESP) Stack Pointer DI (EDI) Destination Index BP (EBP) Base Pointer IP Instruction Pointer %Status Registers FLAGS Status Flags (see FLAGS) %Register Default Segment Valid Overrides BP SS DS, ES, CS SI or DI DS ES, SS, CS DI strings ES None SI strings DS ES, SS, CS ^8088/8086 Effective Address (EA) Calculation % Description Clock Cycles Displacement 6 Base or Index (BX,BP,SI,DI) 5 Displacement+(Base or Index) 9 Base+Index (BP+DI,BX+SI) 7 Base+Index (BP+SI,BX+DI) 8 Base+Index+Displacement (BP+DI,BX+SI) 11 Base+Index+Displacement (BP+SI+disp,BX+DI+disp) 12 - add 4 cycles for word operands at odd addresses - add 2 cycles for segment override - 80188/80186 timings differ from those of the 8088/8086/80286 ^Instruction Clock Cycle Calculation Some instructions require additional clock cycles due to a "Next Instruction Component" identified by a "+m" in the instruction clock cycle listings. This is due to the prefetch queue being purge on a control transfers. Below is the general rule for calculating "m": 88/86 not applicable 286 "m" is the number of bytes in the next instruction 386 "m" is the number of components in the next instruction (the instruction coding (each byte), plus the data and the displacement are all considered components) - all timings are for best case and do not take into account wait states, instruction alignment or the state of the prefetch queue - to convert clocks to nanoseconds divide one microsecond by the processor speed in MegaHertz: ^(1000MHz/(n MHz)) = X nanoseconds - see CPU DETECTING :directives:asm directives ^Macro Assembler Directives ^Processor Code Generation Directives .186 enables assembly of 80186 instructions .286 enables assembly of non privileged 80286 instructions .286C same as .286 .286P enables assembly of all 80286 instructions .287 enabled assembly of 80287 instructions .386 enabled assembly of non privileged 80386 instructions If used before .MODEL segments are defined as 32bits. Causes all segments to default to DWORD alignment. .386P enabled assembly of all 80386 instructions (see .386) .387 enabled assembly of 80387 instructions .8086 default, enables assembly of 8088/8086 instruction .8087 default, enables assembly of 8087 instructions These directives must precede the segment they are to effect. they cannot occur within a segment. ^Memory Model Directives .CODE [name] starts code segment; must follow .MODEL directive .CONST starts a constant data segment with name CONST; must follow .MODEL directive; placed in DGROUP .DATA starts a near data segment for initialized data with name _DATA; must follow .MODEL directive; placed in DGROUP .DATA? starts a near data segment for uninitialized data with name _BSS; must follow .MODEL directive; placed in DGROUP .FARDATA [name] not placed in any group .FARDATA? [name] not placed in any group .MODEL model defines memory model to be one of the following: SMALL, COMPACT, MEDIUM, LARGE or HUGE; must be used prior to any other segment directive .STACK [size] indicates start of stack segment named 'STACK' with size indicating number of bytes to reserve, default is 1k; placed in DGROUP ^Segment Definition, Segment Ordering and Linkage Directives .ALPHA orders segments alphabetically .SEQ orders segments sequentially (default) ASSUME sreg:name [,sreg:name...] selects default segment register to be used by the assembler, not the CPU, for addressing all symbols in the segment or group. Name must be associated with a SEGMENT or GROUP or set to "NOTHING" to indicate no segment register is to be associated. COMM definition [,definition...] defines variables that are both public and external (communal). Can be used in and include file to identify it to each source file without declaring it in each model as extern. Actually defines data once. Communal variables cannot be initialized, and are not guaranteed to be allocated contiguously since these are allocated by the linker. DOSSEG orders segments the same as DOS. This is Microsoft languages default order; causes paragph alignment END [name] marks end of source module and sets program start address (CS:IP) if 'name' is present name ENDP ends procedure 'name' name ENDS ends a segment or structure EXTRN name:type [,name:type...] defines one or more external symbols name GROUP segment[,segment] name LABEL [NEAR|FAR|PROC] defines an entry point; If PROC is specified, it's value depends on the current MODEL NAME pgm ignored since MASM 5.0; used to set module name name PROC [NEAR|FAR] defines procedure; NEAR/FAR has .MODEL default PUBLIC name[,name...] makes symbol 'name' available to other modules name SEGMENT [align][combine][use]['class'] align = BYTE align on byte address (no alignment) = WORD align on even address = DWORD align on DWORD address = PARA align on next 16 byte paragraph = PAGE align on next 256 byte boundary combine = PUBLIC similar named segments are concatenated (CS) = STACK similar named segments are concatenated (SS) = COMMON similar named segment are overlapped = MEMORY similar names segments are concatenated = AT addr segment relative to absolute address = nothing segment is private and loaded independent use = USE16 segments will be 16 bits (if .386) = USE32 segments will be 32 bits (if .386) ^Data Allocation Directives ALIGN n aligns next variable or instruction on a boundary that is a multiple of "n". This can speed memory fetches on 16 and 32 bit CPU'S if aligned. New to MASM 5.0, previous versions used EVEN. Can result in NOP's added to code. [name] DB init[,init...] define byte [name] DD init[,init...] define double word (DWORD, 4 bytes) [name] DF init[,init...] define far word (FWORD, 386, 6 bytes) [name] DQ init[,init...] define quad word (QWORD, 8 bytes) [name] DT init[,init...] define temp word (TBYTE, 10 bytes) [name] DW init[,init...] define word (WORD, 2 bytes) count DUP (init[,init...]) duplicate 'init' 'count' times; DUP can be nested to 17 levels; DUP'ed initial values of (?) don't result in data in the object file but instead increment the next data addr name ENDS end of structure or segment EVEN same as align 2; Aligns data on even boundary ORG expr sets location counter to 'expr'; If 'expr' is '$' the code is ORG'ed at the current loc. name RECORD field[,field...] defines a byte or word variable consisting of bit fields; fields have the format: fieldname:width[=expr]; the sum of all widths must be <= 0 [name] STRUC <[init[,init]]> defines beginning of a structure; Values between <> are initializers; The '<>' symbols are required. ^Logical and Bit Oriented Directives expr1 AND expr2 returns nonzero if any set bit matches expr1 EQ expr2 returns (-1) for true or (0) for false expr1 GE expr2 returns (-1) for true or (0) for false expr1 LE expr2 returns (-1) for true or (0) for false expr1 LT expr2 returns (-1) for true or (0) for false MASK {fldname|record} returns bit mask for bits in record expr1 OR expr2 returns bitwise OR on expr1 and expr2 NOT expr returns 'expr' with all bits reversed expr SHL count returns expr shifted left count times expr SHR count returns expr shifted right count times WIDTH {fldname|record} returns width of field in bit record expr1 XOR expr2 returns bitwise XOR on expr1 and expr2 ^Other Operators and Directives [] index operator, same as addition .MSFLOAT encode floats in Microsoft Real Format .TYPE expr returns byte defining mode and scope of expr name EQU [<]expr[>] assigns expression to name. <> indicates text HIGH expr returns high byte of 'expr' INCLUDE filespec inserts code from 'filespec' into file INCLUDELIB filespec stores link library info in .OBJ file LENGTH var returns number of data objects in DUPed 'var' LOW expr returns low byte of 'expr' expr1 MOD expr2 return remainder of expr1/expr2 OFFSET expr returns offset of expr; When .MODEL is used the offset of a group relative segment refers to the end of the segment type PTR expr forces 'expr' to 'type' SEG expr returns segment of expression SHORT sets type of label to short, less than 128 bytes from start of next instruction SIZE var returns # of bytes allocated by DUP directive THIS type returns an operand of specified type whose offset and segment values are equal to the current location TYPE expr returns type of expression %Program Listing and Documentation Directives .CREF restores listing of cross reference symbols .LALL include macro expansion in listings .LFCOND include false conditional blocks in listings .LIST starts listing of statements .SALL suppress listing of all macro expansions .SFCOND suppress false conditional blocks in listings .XALL start listing of macro expansion .XCREF [name[,name...]] suppress symbols in cross reference .XLIST suppress program listing COMMENT delimiter [text] PAGE [[len],wid] sets page length&width or ejects if no parms SUBTTL text defines program listing subtitle TITLE text defines program listing title %Condition Assembly Directives ELSE else clause for conditional assembly block ENDIF terminates a conditional assembly block IFDEF name conditional assembly if name is defined %Macro Definition Directives ENDM terminates a macro block EXITM exit macro expansion immediately IRP parm, parm in the statements enclosed by the IRP and ENDM will be repeated and replaced with the values of "arg" for each "arg" in the <>. IRPC parm, parm in the statements enclosed by the IRPC and ENDM will be repeated and replaced with the values of each char in the "string" for each character position in the string. "string" should be enclosed in <> if it contains spaces or other separators. LOCAL name[,name...] defines scope symbol as local to a macro name MACRO [parm[,parm...]] defines a macro and it's parameters PURGE name[,name] purges macros from memory REPT expr repeats all statements through ENDM statement 'expr' times %User Message Directives .ERR generates and error .ERR1 generates an error on PASS 1 .ERR2 generates an error on PASS 2 .ERRB generates an error if 'arg' is blank .ERRDEF name generates an error if 'name' is previously defined .ERRDIF[I] , .ERRE expr generates and error is 'expr' is false %OUT text displays 'text' to console %Predefined Equates (available only if simplified segments are used) @curseg contains the current segment @filename current file name without extension @code contains the current code segment @codesize 0 for small & compact, 1 for large, medium & huge @datasize 0 for small & medium, 1 for compact & large, 2=huge @const contains segment of define by .CONST @data contains segment of define by .DATA @data? contains segment of define by .DATA? @fardata contains segment of define by .FARDATA @fardata? contains segment of define by .FARDATA? @stack contains segment of define by .STACK Most of these are only available if the simplified segment system is used. @curseg and @filename are available regardless. %Radix Specifiers .RADIX expr sets radix [2..16] for numbers (dec. default) B binary data specifier Q octal data specifier O octal data specifier D decimal data specifier H hexadecimal data specifier :masm options:assembler options ^Microsoft Assembler Command Line Options ^MASM [options] srcfile[,[objfile][,[lstfile][,[xreffile]]]][;] %Options Definition /A generate segments in alphabetical order /B[size] sets I/O buffer size in K bytes (1..63, default 32) /C generate cross reference file with .CRF extension /D generate PASS 1 listing /Dsym[=val] define symbol for use during assembly /E emulate floating point instructions (for use with HLL) /H list options and command syntax /Ipath include-file search path /L generate listing file with .LST extension /ML case sensitive for all symbols /MU upper case all symbols (default) /MX case sensitive in external and public symbols /N suppress symbol tables in listings /P check for impure code in 286 and 386 protected mode (invalid CS overrides) /S generate segments in the order they are found (default) /T terse message display; display errors only /V verbose message display; includes # lines and symbols /W{0|1|2} assembly warning level 0 = no warnings 1 = severe warnings only 2 = all warnings enabled /X display complete conditional assembly blocks in listing including false conditionals /Z display errors including line numbers to screen /ZD generate line numbers in .OBJ files /ZI generate both symbolic and line number information in .OBJ files %Environment Variables INCLUDE search path for include files MASM default command line options :ea:effective addr calc ^8088/8086 Effective Address (EA) Calculation % Description Clock Cycles Displacement 6 Base or Index (BX,BP,SI,DI) 5 Displacement+(Base or Index) 9 Base+Index (BP+DI,BX+SI) 7 Base+Index (BP+SI,BX+DI) 8 Base+Index+Displacement (BP+DI,BX+SI) 11 Base+Index+Displacement (BP+SI+disp,BX+DI+disp) 12 - add 4 cycles for word operands at odd addresses - add 2 cycles for segment override - 80188/80186 timings differ from those of the 8088/8086/80286 :flags register:8086 flags ^FLAGS - Intel 8086 Family Flags Register ³11³10³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ CF Carry Flag ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ PF Parity Flag ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 0 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ AF Auxiliary Flag ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 0 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ ZF Zero Flag ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ SF Sign Flag ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ TF Trap Flag (Single Step) ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ IF Interrupt Flag ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ DF Direction Flag ³ ³ ³ ³ ³ ³ ÀÄÄÄ OF Overflow flag ³ ³ ³ ³ ÀÄÁÄÄÄ IOPL I/O Privilege Level (286+) ³ ³ ³ ÀÄÄÄÄÄ NT Nested Task Flag (286+) ³ ³ ÀÄÄÄÄÄ 0 ³ ÀÄÄÄÄÄ RF Resume Flag (386) ÀÄÄÄÄÄÄ VM Virtual Mode Flag (386) - see PUSHF POPF STI CLI STD CLD :models:segment names ^Memory Model Programming & Segment Information %Model TINY Data and code fit in one 64K segment. All code and data are accessed via near pointers. SMALL 64k data segment max and 64k code segment max. All code and data are accessed via near pointers. COMPACT 1Mb data segment max and 64K code segment max. Code is accessed via near pointers, data is accessed via far pointers. No array can be greater than 64K MEDIUM 64K data segment max and 1Mb code segment max. Code is accessed via far pointers, data is accessed via near pointers. LARGE 1Mb data segment max and 1Mb code segment max. All code and data are accessed via far pointers. No single element can be greater than 64K. HUGE 1Mb data segment max and 1Mb code segment max. All code and data are accessed via far pointers. This is the only model where arrays can be larger than 64K. In this mode is C will normalize all data pointers to avoid segment wrapping. ^Small Memory Model %Directive Segment Alignment Combine Class .CODE _TEXT WORD PUBLIC 'CODE' .DATA _DATA WORD PUBLIC 'DATA' .CONST CONST WORD PUBLIC 'CONST' .DATA? _BSS WORD PUBLIC 'BSS' .STACK STACK PARA STACK 'STACK' ^Compact Memory Model %Directive Segment Alignment Combine Class .CODE _TEXT WORD PUBLIC 'CODE' .FARDATA FAR_DATA PARA private 'FAR_DATA' .FARDATA? FAR_BSS PARA private 'FAR_BSS' .DATA _DATA WORD PUBLIC 'DATA' .CONST CONST WORD PUBLIC 'CONST' .DATA? _BSS WORD PUBLIC 'BSS' .STACK STACK PARA STACK 'STACK' ^Medium Memory Model %Directive Segment Alignment Combine Class .CODE name_TEXT WORD PUBLIC 'CODE' .DATA _DATA WORD PUBLIC 'DATA' .CONST CONST WORD PUBLIC 'CONST' .DATA? _BSS WORD PUBLIC 'BSS' .STACK STACK PARA STACK 'STACK' ^Large or Huge Memory Models %Directive Segment Alignment Combine Class .CODE name_TEXT WORD PUBLIC 'CODE' .FARDATA FAR_DATA PARA private 'FAR_DATA' .FARDATA? FAR_BSS PARA private 'FAR_BSS' .DATA _DATA WORD PUBLIC 'DATA' .CONST CONST WORD PUBLIC 'CONST' .DATA? _BSS WORD PUBLIC 'BSS' .STACK STACK PARA STACK 'STACK' - all segments fall into DGROUP except for all ???_TEXT, FAR_DATA and FAR_BSS segments :msw:machine status word ^MSW - Machine Status Word (286/386) ³31³ 30-5 ³4³3³2³1³0³ Machine Status Word ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ Protection Enable (PE) ³ ³ ³ ³ ³ ÀÄÄÄÄÄ Math Present (MP) ³ ³ ³ ³ ÀÄÄÄÄÄÄ Emulation (EM) ³ ³ ³ ÀÄÄÄÄÄÄÄ Task Switched (TS) ³ ³ ÀÄÄÄÄÄÄÄÄ Extension Type (ET) ³ ÀÄÄÄÄÄÄÄÄÄÄÄ Reserved ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Paging (PG) Bit 0 PE Protection Enable, switches processor between protected and real mode Bit 1 MP Math Present, controls function of the WAIT instruction Bit 2 EM Emulation, indicates whether coprocessor functions are to be emulated Bit 3 TS Task Switched, set and interrogated by coprocessor on task switches and when interpretting coprocessor instructions Bit 4 ET Extension Type, indicates type of coprocessor in system Bits 5-30 Reserved bit 31 PG Paging, indicates whether the processor uses page tables to translate linear addresses to physical addresses - see SMSW LMSW :aaa ^AAA - Ascii Adjust for Addition Usage: AAA Modifies flags: AF CF (OF,PF,SF,ZF undefined) Changes contents of AL to valid unpacked decimal. The high order nibble is zeroed. % Clocks Size %Operands 86/88 286 386 # Bytes none 8 3 4 1 :aad ^AAD - Ascii Adjust for Division Usage: AAD Modifies flags: SF ZF PF (AF,CF,OF undefined) Used before dividing unpacked decimal numbers. Multiplies AH by 10 and the adds result into AL. Sets AH to zero. % Clocks Size %Operands 86/88 286 386 # Bytes none 60 14 19 2 :aam ^AAM - Ascii Adjust for Multiplication Usage: AAM Modifies flags: PF SF ZF (AF,CF,OF undefined) Used after multiplication of two unpacked decimal numbers, this instruction adjusts an unpacked decimal number. The high order nibble of each byte must be zeroed before using this instruction. % Clocks Size %Operands 86/88 286 386 # Bytes none 83 16 17 2 :aas ^AAS - Ascii Adjust for Subtraction Usage: AAS Modifies flags: AF CF (OF,PF,SF,ZF undefined) Corrects result of a previous unpacked decimal subtraction in AL. High order nibble is zeroed. % Clocks Size %Operands 86/88 286 386 # Bytes none 8 3 4 1 :adc ^ADC - Add With Carry Usage: ADC dest,src Modifies flags: AF CF OF SF PF ZF Sums two binary operands placing the result in the destination. If CF is set, a 1 is added to the destination. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 3 2 2 2 mem,reg 16+EA 7 7 2-4 (W88=24+EA) reg,mem 9+EA 7 6 2-4 (W88=13+EA) reg,immed 4 3 2 3-4 mem,immed 17+EA 7 7 3-6 (W88=23+EA) accum,immed 4 3 2 2-3 - see EA for calculation of Effective Address "EA" :add ^ADD - Arithmetic Addition Usage: ADD dest,src Modifies flags: AF CF OF PF SF ZF Adds "src" to "dest" and replacing the original contents of "dest". Both operands are binary. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 3 2 2 2 mem,reg 16+EA 7 7 2-4 (W88=24+EA) reg,mem 9+EA 7 6 2-4 (W88=13+EA) reg,immed 4 3 2 3-4 mem,immed 17+EA 7 7 3-6 (W88=23+EA) accum,immed 4 3 2 2-3 - see EA for calculation of Effective Address "EA" :and ^AND - Logical And Usage: AND dest,src Modifies flags: CF OF PF SF ZF (AF undefined) Performs a logical AND of the two operands replacing the destination with the result. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 3 2 2 2 mem,reg 16+EA 7 7 2-4 (W88=24+EA) reg,mem 9+EA 7 6 2-4 (W88=13+EA) reg,immed 4 3 2 3-4 mem,immed 17+EA 7 7 3-6 (W88=23+EA) accum,immed 4 3 2 2-3 - see EA for calculation of Effective Address "EA" :arpl ^ARPL - Adjusted Requested Privilege Level of Selector ^(286/386 protected) Usage: ARPL dest,src Modifies flags: ZF Compares the RPL bits of "dest" against "src". If the RPL bits of "dest" are less than "src", the destination RPL bits are set equal to the source RPL bits and the Zero Flag is set. Otherwise the Zero Flag is cleared. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg - 10 20 2 mem,reg - 11 21 4 :bound ^BOUND - Array Index Bound Check (186/188/286/386) Usage: BOUND src,limit Modifies flags: None Array index in source register is checked against upper and lower bounds in memory source. The first word located at "limit" is the lower boundary and the word at "limit+2" is the upper array bound. Interrupt 5 occurs if the source value is less than or higher than the source. % Clocks Size %Operands 86/88 286 386 # Bytes reg16,mem32 - noj=13 noj=10 2 reg32,mem64 - noj=13 noj=10 2 :bsf:bsr ^BSF/BSR - Bit Scan (386 only) Usage: BSF dest,src BSR dest,src Modifies flags: ZF Scans source operand for first bit set. Sets ZF if a bit is found set and loads the destination with an index to first set bit. Clears ZF is no bits are found set. BSF scans forward across bit pattern (0-n) while BSR scans in reverse (n-0). % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg - - 10+3n 3 reg,mem - - 10+3n 3-7 :bt ^BT - Bit Test (386) Usage: BT dest,src Modifies flags: CF The destination bit indexed by the source value is copied into the Carry Flag. % Clocks Size %Operands 86/88 286 386 # Bytes reg16,immed8 - - 3 4-8 mem16,immed8 - - 6 4-8 reg16,reg16 - - 3 3-7 mem16,reg16 - - 12 3-7 :btc ^BTC - Bit Test with Compliment (386) Usage: BTC dest,src Modifies flags: CF The destination bit indexed by the source value is copied into the Carry Flag after being complimented (inverted). % Clocks Size %Operands 86/88 286 386 # Bytes reg16,immed8 - - 6 4-8 mem16,immed8 - - 8 4-8 reg16,reg16 - - 6 3-7 mem16,reg16 - - 13 3-7 :btr ^BTR - Bit Test with Reset (386) Usage: BTR dest,src Modifies flags: CF The destination bit indexed by the source value is copied into the Carry Flag and then cleared in the destination. % Clocks Size %Operands 86/88 286 386 # Bytes reg16,immed8 - - 6 4-8 mem16,immed8 - - 8 4-8 reg16,reg16 - - 6 3-7 mem16,reg16 - - 13 3-7 :bts ^BTS - Bit Test and Set (386) Usage: BTS dest,src Modifies flags: CF The destination bit indexed by the source value is copied into the Carry Flag and then set in the destination. % Clocks Size %Operands 86/88 286 386 # Bytes reg16,immed8 - - 6 4-8 mem16,immed8 - - 8 4-8 reg16,reg16 - - 6 3-7 mem16,reg16 - - 13 3-7 :call ^CALL - Procedure Call Usage: CALL proc-name Modifies flags: None Pushes Instruction Pointer (and Code Segment for far calls) onto stack and loads Instruction Pointer with the address of proc-name. Code continues with execution at CS:IP. % Clocks Size %Operands 86/88 286 386 # Bytes near-proc 19/23 7+m 7+m 3 far-proc 28/36 13+m 17+m 5 reg 16/20 7+m 7+m 2 mem16 21+EA/29+EA 11+m 10+m 2-4 mem32 37+EA/53+EA 16+m 22+m 2-4 - see ASM for information on calculation of "m" - see EA for calculation of Effective Address "EA" :cbw ^CBW - Convert Byte to Word Usage: CBW Modifies flags: None Converts byte in AL to word Value in AX by extending sign of AL throughout register AH. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 3 1 :cdq ^CDQ - Convert Double to Quad (386 only) Usage: CDQ Modifies flags: None Converts signed DWORD in EAX to a signed quad word in EDX:EAX by extending the high order bit of EAX throughout EDX % Clocks Size %Operands 86/88 286 386 # Bytes none - - 2 1 :clc ^CLC - Clear Carry Usage: CLC Modifies flags: CF Clears the Carry Flag. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 2 1 :cld ^CLD - Clear Direction Flag Usage: CLD Modifies flags: DF Clears the Direction Flag causing string instructions to increment the SI and DI index registers. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 2 1 :cli ^CLI - Clear Interrupt Flag (disable) Usage: CLI Modifies flags: IF Disables the maskable hardware interrupts by clearing the Interrupt flag. NMI's and software interrupts are not inhibited. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 3 1 :clts ^CLTS - Clear Task Switched Flag (286/386 privileged) Usage: CLTS Modifies flags: None Clears the Task Switched Flag in the Machine Status Register. This is a privileged operation and is generally used only by operating system code. % Clocks Size %Operands 86/88 286 386 # Bytes none - 2 5 2 :cmc ^CMC - Complement Carry Flag Usage: CMC Modifies flags: CF Toggles (inverts) the Carry Flag % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 2 1 :cmp ^CMP - Compare Usage: CMP dest,src Modifies flags: AF CF OF PF SF ZF Subtracts source from destination and updates the flags but does not save result. Flags can subsequently be checked for conditions. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 3 2 2 2 mem,reg 9+EA 7 5 2-4 (W88=13+EA) reg,mem 9+EA 6 6 2-4 (W88=13+EA) reg,immed 4 3 2 3-4 mem,immed 10+EA 6 5 3-6 (W88=14+EA) accum,immed 4 3 2 2-3 - see EA for calculation of Effective Address "EA" :cmps:cmpsb:cmpsw:cmpsd ^CMPS - Compare String (Byte, Word or Doubleword) Usage: CMPS dest,src CMPSB CMPSW CMPSD (386 only) Modifies flags: AF CF OF PF SF ZF Subtracts destination value from source without saving results. Updates flags based on the subtraction and the index registers (E)SI and (E)DI are incremented or decremented depending on the state of the Direction Flag. CMPSB inc/decrements the index registers by 1, CMPSW inc/decrements by 2, while CMPSD increments or decrements by 4. The REP prefixes can be used to process entire data items. % Clocks Size %Operands 86/88 286 386 # Bytes dest,src 22 8 10 1 (W88=30) :cwd ^CWD - Convert Word to Doubleword Usage: CWD Modifies flags: None Extends sign of word in register AX throughout register DX forming a doubleword quantity in DX:AX. % Clocks Size %Operands 86/88 286 386 # Bytes none 5 2 2 1 :cwde ^CWDE - Convert Word to Extended Doubleword (386 only) Usage: CWDE Modifies flags: None Converts a signed word in AX to a signed doubleword in EAX by extending the sign bit of AX throughout EAX. % Clocks Size %Operands 86/88 286 386 # Bytes none - - 3 1 :daa ^DAA - Decimal Adjust for Addition Usage: DAA Modifies flags: AF CF PF SF ZF (OF undefined) Corrects result (in AL) of a previous BCD addition operation. Contents of AL are changed to a pair of packed decimal digits. % Clocks Size %Operands 86/88 286 386 # Bytes none 4 3 4 1 :das ^DAS - Decimal Adjust for Subtraction Usage: DAS Modifies flags: AF CF PF SF ZF (OF undefined) Corrects result (in AL) of a previous BCD subtraction operation. Contents of AL are changed to a pair of packed decimal digits. % Clocks Size %Operands 86/88 286 386 # Bytes none 4 3 4 1 :dec ^DEC - Decrement Usage: DEC dest Modifies flags: AF OF PF SF ZF Unsigned binary subtraction of one from the destination. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 3 2 2 2 mem 15+EA 7 6 2-4 reg16/32 3 2 2 1 - see EA for calculation of Effective Address "EA" :div ^DIV - Divide Usage: DIV src Modifies flags: (AF,CF,OF,PF,SF,ZF undefined) Unsigned binary division of accumulator by source. If the source divisor is a byte value then AX is divided by "src" and the quotient is placed in AL and the remainder in AH. If source operand is a word value, then DX:AX is divided by "src" and the quotient is stored in AX and the remainder in DX. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 80-90 14 14 2 reg16 144-162 22 22 2 reg32 - - 38 2 mem8 (86-96)+EA 17 17 2-4 mem16 (150-168)+EA 25 25 2-4 (W88=158-176+EA) mem32 - - 41 2-4 - see EA for calculation of Effective Address "EA" :enter ^ENTER - Make Stack Frame (188/186/286/386) Usage: ENTER locals,level Modifies flags: None Modifies stack for entry to procedure for high level language. Operand "locals" specifies the amount of storage to be allocated on the stack. "Level" specifies the nesting level of the routine. Paired with the LEAVE instruction, this is an efficient method of entry and exit to procedures. % Clocks Size %Operands 86/88 286 386 # Bytes immed16,0 - 11 10 4 immed16,1 - 15 12 4 immed16,immed8 - 12+4(n-1) 15+4(n-1) 4 :esc ^ESC - Escape Usage: ESC immed,src Modifies flags: None Provides access to the data bus for other resident processors. The CPU treats it as a NOP but places memory operand on bus. % Clocks Size %Operands 86/88 286 386 # Bytes immed,reg 2 9-20 ? 2 immed,mem 2 9-20 ? 2-4 :hlt ^HLT - Halt CPU Usage: HLT Modifies flags: None Halts CPU until RESET line activated, NMI or maskable interrupt received. The CPU becomes dormant but retains the current CS:IP for later restart. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 5 1 :idiv ^IDIV - Divide Usage: IDIV src Modifies flags: (AF,CF,OF,PF,SF,ZF undefined) Signed binary division of accumulator by source. If source is a byte value, AX is divided by "src" and the quotient is stored in AL and the remainder in AH. If source is a word value, DX:AX is divided by "src", and the quotient is stored in AL and the remainder in DX. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 101-112 17 19 2 reg16 165-184 25 27 2 reg32 - - 43 2 mem8 (107-118)+EA 20 22 2-4 mem16 (171-190)+EA 38 30 2-4 (W88=175-194) mem32 - - 46 2-4 - see EA for calculation of Effective Address "EA" :imul ^IMUL - Signed Multiply Usage: IMUL src IMUL src,immed (286/386) IMUL dest,src,immed8 (286/386) IMUL dest,src (386) Modifies flags: CF OF (AF,PF,SF,ZF undefined) Signed multiplication of accumulator by "src" with result placed in the accumulator. If the source operand is a byte value, it is multiplied by AL and the result stored in AX. If the source operand is a word value it is multiplied by AX and the result is stored in DX:AX. Other variation of this instruction allow specification of source and destination registers as well as a third immediate factor. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 80-98 13 9-14 2 reg16 128-154 21 9-22 2 reg32 - - 9-38 2 mem8 86-104 16 12-17 2-4 mem16 134-160 24 12-25 2-4 mem32 - - 12-41 2-4 reg8,immed * - 21 9-14 3 reg16,immed - 21 9-22 3 reg32,immed - 21 9-38 3-6 reg8,reg8,immed * - 2 9-14 3-6 reg16,reg16,immed - 2 9-22 3-6 reg32,reg32,immed - 21 9-38 3-6 reg8,mem8,immed * - 24 12-17 3-6 reg16,mem16,immed - 24 12-25 3-6 reg32,mem32,immed - 24 12-41 3-6 reg16,reg16 - - 9-22 3-5 reg32,reg32 - - 9-38 3-5 reg16,mem16 - - 12-25 3-5 reg32,mem32 - - 12-41 3-5 * Check your assembler guide for actual operand formats :in ^IN - Input Byte or Word From Port Usage: IN accum,port Modifies flags: None A byte or word is read from "port" and placed in AL or AX respectively. If the port number is in the range of 0-255 it can be specified as an immediate, otherwise the port number must be specified in DX. Valid port ranges on the PC are 0-1024, though values through 65535 may be specified and recognized by third party vendors and PS/2's. % Clocks Size %Operands 86/88 286 386 # Bytes accum,immed8 10/14 5 12 2 accum,DX 8/12 5 13 1 :inc ^INC - Increment Usage: INC dest Modifies flags: AF OF PF SF ZF Adds one to destination unsigned binary operand. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 3 2 2 2 reg16 3 2 2 1 reg32 3 2 2 1 mem 15+EA 7 6 2-4 (W88=23+EA) - see EA for calculation of Effective Address "EA" :ins:insb:insw:insd ^INS - Input String from Port (188/186/286/386) Usage: INS dest,port INSB INSW INSD (386) Modifies flags: None Loads data from port to the destination ES:(E)DI (even if a destination operand is supplied). (E)DI is adjusted by the size of the operand and increased if the Direction Flag is cleared and decreased if the Direction Flag is set. For INSB, INSW, INSD no operands are allowed and the size is determined by the mnemonic. % Clocks Size %Operands 86/88 286 386 # Bytes dest,port - 5 15 1 none - 5 15 1 :int ^INT - Interrupt Usage: INT interrupt-type Modifies flags: TF IF Initiates a software interrupt by pushing the flags, clearing the Trap and Interrupt Flags, pushing CS followed by IP and loading CS:IP with the value found in the interrupt vector table. Execution then begins at the location addressed by the new CS:IP % Clocks Size %Operands 86/88 286 386 # Bytes immed8 51/71 23+m 33 1 3 (constant) 52/72 23 33 2 - see ASM for information on calculation of "m" :into ^INTO - Interrupt on Overflow Usage: INTO Modifies flags: IF TF If the Overflow Flag is set this instruction generates an INT 4 which causes the code addressed by 0000:0010 to be executed. % Clocks Size %Operands 86/88 286 386 # Bytes none 53/73 24+m 35 1 if no jump 4 3 3 - see ASM for information on calculation of "m" :iret:iretd ^IRET/IRETD - Interrupt Return Usage: IRET IRETD (386 only) Modifies flags: AF CF DF IF PF SF TF ZF Returns control to point of interruption by popping IP, CS and then the Flags from the stack and continues execution at this location. CPU exception interrupts will return to the instruction that cause the exception because the CS:IP placed on the stack during the interrupt is the address of the offending instruction. % Clocks Size %Operands 86/88 286 386 # Bytes iret 32/44 17+m 22 1 iretd - - 22 1 - see ASM for information on calculation of "m" :j... ^Jump Instructions Table %Mnemonic Meaning Jump Condition JA Jump if Above CF=0 and ZF=0 JAE Jump if Above or Equal CF=0 JB Jump if Below CF=1 JBE Jump if Below or Equal CF=1 or ZF=1 JC Jump if Carry CF=1 JCXZ Jump if CX Zero CX=0 JE Jump if Equal ZF=1 JG Jump if Greater (signed) ZF=0 and SF=OF JGE Jump if Greater or Equal (signed) SF=OF JL Jump if Less (signed) SF != OF JLE Jump if Less or Equal (signed) ZF=1 or SF != OF JMP Unconditional Jump unconditional JNA Jump if Not Above CF=1 or ZF=1 JNAE Jump if Not Above or Equal CF=1 JNB Jump if Not Below CF=0 JNBE Jump if Not Below or Equal CF=0 and ZF=0 JNC Jump if Not Carry CF=0 JNE Jump if Not Equal ZF=0 JNG Jump if Not Greater (signed) ZF=1 or SF != OF JNGE Jump if Not Greater or Equal (signed) SF != OF JNL Jump if Not Less (signed) SF=OF JNLE Jump if Not Less or Equal (signed) ZF=0 and SF=OF JNO Jump if Not Overflow (signed) OF=0 JNP Jump if No Parity PF=0 JNS Jump if Not Signed (signed) SF=0 JNZ Jump if Not Zero ZF=0 JO Jump if Overflow (signed) OF=1 JP Jump if Parity PF=1 JPE Jump if Parity Even PF=1 JPO Jump if Parity Odd PF=0 JS Jump if Signed (signed) SF=1 JZ Jump if Zero ZF=1 % Clocks Size %Operands 86/88 286 386 # Bytes Jx label 16 7+m 7+m 2 no jump 4 3 3 Jx near-label - - 7+m 4 - see JCXZ and JMP for their respective timings - It's a good programming practice to organize code so the expected case is executed without a jump since the actual jump takes longer to execute than falling through the test. - see FLAGS :ja:jnbe ^JA/JNBE - Jump Above / Jump Not Below or Equal Usage: JA/JNBE label Modifies flags: None Causes execution to branch to "label" if the Carry Flag and Zero Flag are both clear. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 label - - 7+m 4 - see ASM for information on calculation of "m" :jae:jnb ^JAE/JNB - Jump Above or Equal / Jump on Not Below Usage: JAE label JNB label Modifies flags: None Causes execution to branch to "label" if the Carry Flag is clear. Functionally similar to JNC. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 label - - 7+m 4 - see ASM for information on calculation of "m" :jb:jnae ^JB/JNAE - Jump Below / Jump Not Above or Equal Usage: JB label JNAE label Modifies flags: None Causes execution to branch to "label" if the Carry Flag is set. Functionally similar to JC. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jbe:jna ^JBE/JNA - Jump Below or Equal / Jump Not Above Usage: JBE label JNA label Modifies flags: None Causes execution to branch to "label" if the Carry Flag or the Zero Flag is set. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jc ^JC - Jump on Carry Usage: JC label Modifies flags: None Causes execution to branch to "label" if the Carry Flag is set. Functionally similar to JB and JNAE. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jcxz:jecxz ^JCXZ/JECXZ - Jump if Register (E)CX is Zero Usage: JCXZ label JECXZ label (386 only) Modifies flags: None Causes execution to branch to "label" if register CX is zero. Uses unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 18 8+m 9+m 2 no jump 6 4 5 - see ASM for information on calculation of "m" :je:jz ^JE/JZ - Jump Equal / Jump Zero Usage: JE label JZ label Modifies flags: None Causes execution to branch to "label" if the Zero Flag is set. Uses unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jg:jnle ^JG/JNLE - Jump Greater / Jump Not Less or Equal Usage: JG label JNLE label Modifies flags: None Causes execution to branch to "label" if the Zero Flag is clear or the Sign Flag equals the Overflow Flag. Signed comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jge:jnl ^JGE/JNL - Jump Greater or Equal / Jump Not Less Usage: JGE label JNL label Modifies flags: None Causes execution to branch to "label" if the Sign Flag equals the Overflow Flag. Signed comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jl:jnge ^JL/JNGE - Jump Less / Jump Not Greater or Equal Usage: JL label JNGE label Modifies flags: None Causes execution to branch to "label" if the Sign Flag is not equal to Overflow Flag. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jle:jng ^JLE/JNG - Jump Less or Equal / Jump Not Greater Usage: JLE label JNG label Modifies flags: None Causes execution to branch to "label" if the Zero Flag is set or the Sign Flag is not equal to the Overflow Flag. Signed comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jmp ^JMP - Unconditional Jump Usage: JMP target Modifies flags: None Unconditionally transfers control to "label". Jumps by default are within -32768 to 32767 bytes from the instruction following the jump. NEAR and SHORT jumps cause the IP to be updated while FAR jumps cause CS and IP to be updated. % Clocks Size %Operands 86/88 286 386 # Bytes short-label 15 7+m 7+m 2 near-label 15 7+m 7+m 3 (or 5,7 on 386) far-label 15 11+m 12+m 5 reg16 11 7+m 7+m 2 reg32 - - 7+m 2 mem16 18+EA 11+m 10+m 2 mem32 - - 10+m 2 mem32 24+EA 15+m 12+m 2 mem48 - - 12+m 2 - see ASM for information on calculation of "m" - see EA for calculation of Effective Address "EA" :jnc ^JNC - Jump Not Carry Usage: JNC label Modifies flags: None Causes execution to branch to "label" if the Carry Flag is clear. Functionally similar to JAE or JNB. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jne:jnz ^JNE/JNZ - Jump Not Equal / Jump Not Zero Usage: JNE label JNZ label Modifies flags: None Causes execution to branch to "label" if the Zero Flag is clear. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jno ^JNO - Jump Not Overflow Usage: JNO label Modifies flags: None Causes execution to branch to "label" if the Overflow Flag is clear. Signed comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jns ^JNS - Jump Not Signed Usage: JNS label Modifies flags: None Causes execution to branch to "label" if the Sign Flag is clear. Signed comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jnp:jpo ^JNP/JPO - Jump Not Parity / Jump Parity Odd Usage: JNP/JPO label Modifies flags: None Causes execution to branch to "label" if the Parity Flag is clear. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jo ^JO - Jump on Overflow Usage: JO label Modifies flags: None Causes execution to branch to "label" if the Overflow Flag is set. Signed comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :jp:jpe ^JP/JPE - Jump on Parity / Jump on Parity Even Usage: JP/JPE label Modifies flags: None Causes execution to branch to "label" if the Parity Flag is set. Unsigned comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :js ^JS - Jump Signed Usage: JS label Modifies flags: None Causes execution to branch to "label" if the Sign Flag is set. Signed comparision. % Clocks Size %Operands 86/88 286 386 # Bytes label 16 7+m 7+m 2 no jump 4 3 3 near-label - - 7+m 4 - see ASM for information on calculation of "m" :lahf ^LAHF - Load Register AH From Flags Usage: LAHF Modifies flags: None Copies bits 0-7 of the flags register into AH. This includes flags AF, CF, PF, SF and ZF other bits are undefined. % Clocks Size %Operands 86/88 286 386 # Bytes none 4 2 2 1 :lar ^LAR - Load Access Rights (286/386 protected) Usage: LAR dest,src Modifies flags: ZF The high byte of the of the destination register is overwritten by the value of the access rights byte and the low order byte is zeroed depending on the selection in the source operand. The Zero Flag is set if the load operation is successful. % Clocks Size %Operands 86/88 286 386 # Bytes reg16,reg16 - 14 15 3 reg32,reg32 - - 15 3 reg16,mem16 - 16 16 3-7 reg32,mem32 - - 16 3-7 :lds ^LDS - Load Pointer Using DS Usage: LDS dest,src Modifies flags: None Loads 32-bit pointer from memory source to destination register and DS. The offset is placed in the destination register and the segment is placed in DS. To use this instruction the word at the lower memory address must contain the offset and the word at the higher address must contain the segment. This simplifies the loading of far pointers from the stack and the interrupt vector table. % Clocks Size %Operands 86/88 286 386 # Bytes reg16,mem32 16+EA 7 7 2-4 - see EA for calculation of Effective Address "EA" :lea ^LEA - Load Effective Address Usage: LEA dest,src Modifies flags: None Transfers offset address of "src" to the destination register. % Clocks Size %Operands 86/88 286 386 # Bytes reg,mem 2+EA 3 2 2-4 - see EA for calculation of Effective Address "EA" :leave ^LEAVE - Restore Stack for Procedure Exit (188/186/286/386) Usage: LEAVE Modifies flags: None Releases the local variables created by the previous ENTER instruction by restoring SP and BP to their condition before the procedure stack frame was initialized. % Clocks Size %Operands 86/88 286 386 # Bytes none - 5 4 1 :les ^LES - Load Pointer Using ES Usage: LES dest,src Modifies flags: None Loads 32-bit pointer from memory source to destination register and ES. The offset is placed in the destination register and the segment is placed in ES. To use this instruction the word at the lower memory address must contain the offset and the word at the higher address must contain the segment. This simplifies the loading of far pointers from the stack and the interrupt vector table. % Clocks Size %Operands 86/88 286 386 # Bytes reg,mem 16+EA/24+EA 7 7 2-4 - see EA for calculation of Effective Address "EA" :lfs ^LFS - Load Pointer Using FS (386 only) Usage: LFS dest,src Modifies flags: None Loads 32-bit pointer from memory source to destination register and FS. The offset is placed in the destination register and the segment is placed in FS. To use this instruction the word at the lower memory address must contain the offset and the word at the higher address must contain the segment. This simplifies the loading of far pointers from the stack and the interrupt vector table. % Clocks Size %Operands 86/88 286 386 # Bytes reg,mem - - 7 5-7 :lgdt ^LGDT - Load Global Descriptor Table (286/386 privileged) Usage: LGDT src Modifies flags: None Loads a value from an operand into the Global Descriptor Table register. % Clocks Size %Operands 86/88 286 386 # Bytes mem64 - 11 11 5 - see GDT :lidt ^LIDT - Load Interrupt Descriptor Table (286/386 privileged) Usage: LIDT src Modifies flags: None Loads a value from an operand into the Interrupt Descriptor Table register. % Clocks Size %Operands 86/88 286 386 # Bytes mem64 - 12 11 5 :lgs ^LGS - Load Pointer Using GS (386 only) Usage: LGS dest,src Modifies flags: None Loads 32-bit pointer from memory source to destination register and GS. The offset is placed in the destination register and the segment is placed in GS. To use this instruction the word at the lower memory address must contain the offset and the word at the higher address must contain the segment. This simplifies the loading of far pointers from the stack and the interrupt vector table. % Clocks Size %Operands 86/88 286 386 # Bytes reg,mem - - 7 5-7 :lldt ^LLDT - Load Local Descriptor Table (286/386 privileged) Usage: LLDT src Modifies flags: None Loads a value from an operand into the Local Descriptor Table register. % Clocks Size %Operands 86/88 286 386 # Bytes reg16 - 17 20 3 mem16 - 19 24 5 :lmsw ^LMSW - Load Machine Status Word (286/386 privileged) Usage: LMSW src Modifies flags: None Loads the Machine Status Word from data found at "src" % Clocks Size %Operands 86/88 286 386 # Bytes reg16 - 3 10 3 mem16 - 6 13 5 - see MSW :lsl ^LSL - Load Segment Limit (286/386 protected) Usage: LSL dest,src Modifies flags: ZF Loads the segment limit of a selector into the destination register if the selector is valid and visible at the current privilege level. If loading is successful the Zero Flag is set, otherwise it is cleared. % Clocks Size %Operands 86/88 286 386 # Bytes reg16,reg16 - 14 20/25 3 reg32,reg32 - - 20/25 3 reg16,mem16 - 16 21/26 5 reg32,mem32 - - 21/26 5 - 386 times are for byte granular/page granular :lss ^LSS - Load Pointer Using SS (386 only) Usage: LSS dest,src Modifies flags: None Loads 32-bit pointer from memory source to destination register and SS. The offset is placed in the destination register and the segment is placed in SS. To use this instruction the word at the lower memory address must contain the offset and the word at the higher address must contain the segment. This simplifies the loading of far pointers from the stack and the interrupt vector table. % Clocks Size %Operands 86/88 286 386 # Bytes reg,mem - - 7 5-7 :lock ^LOCK - Lock Bus Usage: LOCK LOCK: (386 prefix) Modifies flags: None This instruction is a prefix that causes the CPU assert bus lock signal during the execution of the next instruction. Used to avoid two processors from updating the same data location. The 286 always asserts lock during an XCHG with memory operands. This should only be used to lock the bus prior to XCHG, MOV, IN and OUT instructions. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 0 0 1 :lods:lodsb:lodsw:lodsd ^LODS - Load String (Byte, Word or Double) Usage: LODS src LODSB LODSW LODSD (386) Modifies flags: None Transfers string element addressed by DS:SI (even if an operand is supplied) to the accumulator. SI is incremented based on the size of the operand or based on the instruction used. If the Direction Flag is set SI is decremented, if the Direction Flag is clear SI is incremented. Use with REP prefixes. % Clocks Size %Operands 86/88 286 386 # Bytes src 12/16 5 5 1 :loop ^LOOP - Decrement CX and Loop if CX Not Zero Usage: LOOP label Modifies flags: None Decrements CX by 1 and transfers control to "label" if CX is not Zero. The "label" operand must be within -128 or 127 bytes of the instruction following the loop instruction % Clocks Size %Operands 86/88 286 386 # Bytes label 17 8+m 11+m 2 no jump 5 4 ? - see ASM for information on calculation of "m" :loope:loopz ^LOOPE/LOOPZ - Loop While Equal / Loop While Zero Usage: LOOPE label LOOPZ label Modifies flags: None Decrements CX by 1 (without modifying the flags) and transfers control to "label" if CX != 0 and the Zero Flag is set. The "label" operand must be within -128 or 127 bytes of the instruction following the loop instruction. % Clocks Size %Operands 86/88 286 386 # Bytes label 18 8+m 11+m 2 no jump 6 4 ? - see ASM for information on calculation of "m" :loopnz:loopne ^LOOPNZ/LOOPNE - Loop While Not Zero / Loop While Not Equal Usage: LOOPNZ label LOOPNE label Modifies flags: None Decrements CX by 1 (without modifying the flags) and transfers control to "label" if CX != 0 and the Zero Flag is clear. The "label" operand must be within -128 or 127 bytes of the instruction following the loop instruction. % Clocks Size %Operands 86/88 286 386 # Bytes label 19 8+m 11+m 2 no jump 5 4 ? - see ASM for information on calculation of "m" :ltr ^LTR - Load Task Register (286/386 privileged) Usage: LTR src Modifies flags: None Loads the current task register with the value specified in "src". % Clocks Size %Operands 86/88 286 386 # Bytes reg16 - 17 23 3 mem16 - 19 27 5 :mov ^MOV - Move Byte or Word Usage: MOV dest,src Modifies flags: None Copies byte or word from the source operand to the destination operand. If the destination is SS interrupts are disabled except on early buggy 808x CPUs. Some CPUs disable interrupts if the destination is any of the segment registers % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 2 2 2 2 mem,reg 9+EA 3 2 2-4 (W88=13+EA) reg,mem 8+EA 5 4 2-4 (W88=12+EA) mem,immed 10+EA 3 2 3-6 (W88=14+EA) reg,immed 4 2 2 2-3 mem,accum 10 3 2 3 (W88=14) accum,mem 10 5 4 3 (W88=14) segreg,reg16 2 2 2 2 segreg,mem16 8+EA/12+EA 5 5 2-4 reg16,segreg 2 2 2 2 mem16,segreg 9+EA/13+EA 3 2 2-4 reg32,controlreg * - - 6 3 controlreg,reg32 * - - 10/4/5 3 reg32,debugreg * - - 22/14 3 debugreg,reg32 * - - 22/16 3 reg32,testreg * - - 12 3 testreg,reg32 * - - 12 3 * Indicates moves to or from general purpose registers to one of the following 386 special registers: controlreg is one of the following: CR0,CR2,CR3 debugreg is one of the following: DR0, DR1, DR2, DR3, DR6, DR7 testreg is one of the following: TR6, TR7 - see EA for calculation of Effective Address "EA" :movs:movsb:movsw:movsd ^MOVS - Move String (Byte or Word) Usage: MOVS dest,src MOVSB MOVSW MOVSD Modifies flags: None Copies data from addressed by DS:SI (even if operands are given) to the location ES:DI destination and updates SI and DI based on the size of the operand or instruction used. SI and DI are incremented when the Direction Flag is cleared and decremented when the Direction Flag is Set. Use with REP prefixes. % Clocks Size %Operands 86/88 286 386 # Bytes dest,src 18 5 7 1 (W88=26) :movsx ^MOVSX - Move with Sign Extend (386 only) Usage: MOVSX dest,src Modifies flags: None Copies the value of the source operand to the destination register with the sign extended. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg - - 3 3 reg,mem - - 6 3-7 :movzx ^MOVZX - Move with Zero Extend (386 only) Usage: MOVZX dest,src Modifies flags: None Copies the value of the source operand to the destination register with the zeroes extended. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg - - 3 3 reg,mem - - 6 3-7 :mul ^MUL - Unsigned Multiply Usage: MUL src Modifies flags: CF OF (AF,PF,SF,ZF undefined) Unsigned multiply of the accumulator by the source. If "src" is a byte value, then AL is used as the other multiplicand and the result is placed in AX. If "src" is a word value, then AX is multiplied by "src" and DX:AX receives the result. If "src" is a double word value, then EAX is multiplied by "src" and EDX:EAX receives the result. The 386 uses an early out algorithm which makes multiplying any size value in EAX as fast as in the 8 or 16 bit registers. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 70-77 13 9-14 2 reg16 118-113 21 9-22 2 reg32 - - 9-38 2-4 mem8 76-83+EA 16 12-17 2-4 mem16 124-139+EA 24 12-25 2-4 mem32 - - 12-21 2-4 - see EA for calculation of Effective Address "EA" - see IMUL :neg ^NEG - Two's Complement Negation Usage: NEG dest Modifies flags: AF CF OF PF SF ZF Subtracts the destination from 0 and saves the 2s complement of "dest" back into "dest". % Clocks Size %Operands 86/88 286 386 # Bytes reg 3 2 2 2 mem 16+EA 7 6 2-4 (W88=24+EA) - see EA for calculation of Effective Address "EA" :nop ^NOP - No Operation (90h) Usage: NOP Modifies flags: None This is a do nothing instruction. It results in occupation of both space and time and is most useful for patching code segments. % Clocks Size %Operands 86/88 286 386 # Bytes none 3 3 3 1 :not ^NOT - One's Compliment Negation (Logical NOT) Usage: NOT dest Modifies flags: None Inverts the bits of the "dest" operand forming the 1s complement. % Clocks Size %Operands 86/88 286 386 # Bytes reg 3 2 2 2 mem 16+EA 7 6 2-4 (W88=24+EA) - see EA for calculation of Effective Address "EA" :or ^OR - Inclusive Logical OR Usage: OR dest,src Modifies flags: CF OF PF SF ZF (AF undefined) Logical inclusive OR of the two operands returning the result in the destination. Any bit set in either operand will be set in the destination. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 3 2 2 2 mem,reg 16+EA 7 7 2-4 (W88=24+EA) reg,mem 9+EA 7 6 2-4 (W88=13+EA) reg,immed 4 3 2 3-4 mem8,immed8 17+EA 7 7 3-6 mem16,immed16 25+EA 7 7 3-6 accum,immed 4 3 2 2-3 - see EA for calculation of Effective Address "EA" :out ^OUT - Output Data to Port Usage: OUT port,accum Modifies flags: None Transfers byte in AL or word in AX to the specified hardware port address. If the port number is in the range of 0-255 it can be specified as an immediate. If greater than 255 then the port number must be specified in DX. Since the PC only decodes 10 bits of the port address, values over 1023 can only be decoded by third party vendor equipment and also map to the port range 0-1023. % Clocks Size %Operands 86/88 286 386 # Bytes immed8,accum 10/14 3 10 2 DX,accum 8/12 3 11 1 :outs:outsb:outsw:outsd ^OUTS - Output String to Port (188/186/286/386) Usage: OUTS port,src OUTSB OUTSW OUTSD (386) Modifies flags: None Transfers a byte, word or doubleword from "src" to the hardware port specified in DX. For instructions with no operands the "src" is located at DS:SI and SI is incremented or decremented by the size of the operand or the size dictated by the instruction format. When the Direction Flag is set SI is decremented, when clear, SI is incremented. If the port number is in the range of 0-255 it can be specified as an immediate. If greater than 255 then the port number must be specified in DX. Since the PC only decodes 10 bits of the port address, values over 1023 can only be decoded by third party vendor equipment and also map to the port range 0-1023. % Clocks Size %Operands 86/88 286 386 # Bytes port,src - 5 14 1 :pop ^POP - Pop Word off Stack Usage: POP dest Modifies flags: None Transfers word at the current stack top (SS:SP) to the destination then increments SP by two to point to the new stack top. CS is not a valid destination. % Clocks Size %Operands 86/88 286 386 # Bytes reg16/32 8/12 5 4 1 mem16/32 17+EA/25+EA 5 5 2-4 segreg 8/12 5 7 1 - see EA for calculation of Effective Address "EA" :popa:popad ^POPA/POPAD - Pop All Registers onto Stack (188/186/286/386) Usage: POPA POPAD (386) Modifies flags: None Pops the top 8 words off the stack into the 8 general purpose 16/32 bit registers. Registers are popped in the following order: (E)DI, (E)SI, (E)BP, (E)SP, (E)DX, (E)CX and (E)AX. The (E)SP value popped from the stack is actually discarded. % Clocks Size %Operands 86/88 286 386 # Bytes none - 19 24 1 :popf:popfd ^POPF/POPFD - Pop Flags off Stack Usage: POPF POPFD (386) Modifies flags: all flags Pops word/doubleword from stack into the Flags Register and then increments SP by 2 (for POPF) or 4 (for POPFD). % Clocks Size %Operands 86/88 286 386 # Bytes none 8/12 5 5 1 :push ^PUSH - Push Word onto Stack Usage: PUSH src PUSH immed (188/186/286/386) Modifies flags: None Decrements SP by the size of the operand (two or four, byte values are sign extended) and transfers one word from source to the stack top (SS:SP). % Clocks Size %Operands 86/88 286 386 # Bytes reg16/32 11/15 3 2 1 mem16/32 16+EA/24+EA 5 5 2-4 segreg 10/14 3 2 1 immed - 3 2 2-3 - see EA for calculation of Effective Address "EA" :pusha:pushad ^PUSHA/PUSHAD - Push All Registers onto Stack (188/186/286/386) Usage: PUSHA PUSHAD (386) Modifies flags: None Pushes all general purpose registers onto the stack in the following order: (E)AX, (E)CX, (E)DX, (E)BX, (E)SP, (E)BP, (E)SI, (E)DI. The value of SP is the value before the actual push of SP. % Clocks Size %Operands 86/88 286 386 # Bytes none - 17 18 1 :pushf:pushfd ^PUSHF/PUSHFD - Push Flags onto Stack Usage: PUSHF PUSHFD (386 only) Modifies flags: None Transfers the Flags Register onto the stack. PUSHF saves a 16 bit value while PUSHFD saves a 32 bit value. % Clocks Size %Operands 86/88 286 386 # Bytes none 10/14 3 4 1 :rcl ^RCL - Rotate Through Carry Left Usage: RCL dest,count Modifies flags: CF OF Rotates the bits in the destination to the left "count" times with all data pushed out the left side re-entering on the right. The Carry Flag holds the last bit rotated out. % Clocks Size %Operands 86/88 286 386 # Bytes reg,1 2 2 9 2 mem,1 15+EA 7 10 2-4 (W88=23+EA) reg,CL 8+4n 5+n 9 2 mem,CL 20+EA+4n 8+n 10 2-4 (W88=28+EA+4n) reg,immed8 - 5+n 9 3 mem,immed8 - 8+n 10 3-5 - see EA for calculation of Effective Address "EA" :rcr ^RCL - Rotate Through Carry Right Usage: RCR dest,count Modifies flags: CF OF Rotates the bits in the destination to the right "count" times with all data pushed out the right side re-entering on the left. The Carry Flag holds the last bit rotated out. % Clocks Size %Operands 86/88 286 386 # Bytes reg,1 2 2 9 2 mem,1 15+EA 7 10 2-4 (W88=23+EA) reg,CL 8+4n 5+n 9 2 mem,CL 20+EA+4n 8+n 10 2-4 (W88=28+EA+4n) reg,immed8 - 5+n 9 3 mem,immed8 - 8+n 10 3-5 - see EA for calculation of Effective Address "EA" :rep ^REP - Repeat String Operation Usage: REP Modifies flags: None Repeats execution of string instructions while CX != 0. After each string operation, CX is decremented and the Zero Flag is tested. The combination of a repeat prefix and a segment override on CPU's before the 386 may result in errors if an interrupt occurs before CX=0. The following code shows code that is susceptible to this and how to avoid it: again: rep movs byte ptr ES:[DI],ES:[SI] ; vulnerable instr. jcxz next ; continue if REP successful loop again ; interrupt goofed count next: % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 2 1 :repe:repz ^REPE/REPZ - Repeat Equal / Repeat Zero Usage: REPE REPZ Modifies flags: None Repeats execution of string instructions while CX != 0 and the Zero Flag is set. CX is decremented and the Zero Flag tested after each string operation. The combination of a repeat prefix and a segment override on processors other than the 386 may result in errors if an interrupt occurs before CX=0. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 2 1 :repne:repnz ^REPNE/REPNZ - Repeat Not Equal / Repeat Not Zero Usage: REPNE REPNZ Modifies flags: None Repeats execution of string instructions while CX != 0 and the Zero Flag is clear. CX is decremented and the Zero Flag tested after each string operation. The combination of a repeat prefix and a segment override on processors other than the 386 may result in errors if an interrupt occurs before CX=0. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 2 1 :ret:retf:retn ^RET/RETF - Return From Procedure Usage: RET [n bytes] RETF [n bytes] RETN [n bytes] Modifies flags: None Transfers control from a procedure back to the instruction address saved on the stack. "n bytes" is an optional number of bytes to release. Far returns pop the IP followed by the CS, while near returns pop only the IP register. % Clocks Size %Operands 86/88 286 386 # Bytes retn 16/20 11+m 10+m 1 retn immed8 20/24 11+m 10+m 3 retf 26/34 15+m 18+m 1 retf immed8 25/33 15+m 18+m 3 - see ASM for information on calculation of "m" :rol ^ROL - Rotate Left Usage: ROL dest,count Modifies flags: CF OF Rotates the bits in the destination to the left "count" times with all data pushed out the left side re-entering on the right. The Carry Flag will contain the value of the last bit rotated out. % Clocks Size %Operands 86/88 286 386 # Bytes reg,1 2 2 3 2 mem,1 15+EA 7 7 2-4 (W88=23+EA) reg,CL 8+4n 5+n 3 2 mem,CL 20+EA+4n 8+n 7 2-4 (W88=28+EA+4n) reg,immed8 - 5+n 3 3 mem,immed8 - 8+n 7 3-5 - see EA for calculation of Effective Address "EA" :ror ^ROR - Rotate Right Usage: ROR dest,count Modifies flags: CF OF Rotates the bits in the destination to the right "count" times with all data pushed out the right side re-entering on the left. The Carry Flag will contain the value of the last bit rotated out. % Clocks Size %Operands 86/88 286 386 # Bytes reg,1 2 2 3 2 mem,1 15+EA 7 7 2-4 (W88=23+EA) reg,CL 8+4n 5+n 3 2 mem,CL 20+EA+4n 8+n 7 2-4 (W88=28+EA+4n) reg,immed8 - 5+n 3 3 mem,immed8 - 8+n 7 3-5 - see EA for calculation of Effective Address "EA" :sahf ^SAHF - Store AH Register into FLAGS Usage: SAHF Modifies flags: AF CF PF SF ZF Transfers bits 0-7 of AH into the Flags Register. This includes AF, CF, PF, SF and ZF. % Clocks Size %Operands 86/88 286 386 # Bytes none 4 2 3 1 :sal:shl ^SAL/SHL - Shift Arithmetic Left / Shift Logical Left Usage: SAL dest,count SHL dest,count Modifies flags: CF OF PF SF ZF (AF undefined) Shifts the destination left by "count" bits with zeroes shifted in on right. The Carry Flag contains the last bit shifted out. % Clocks Size %Operands 86/88 286 386 # Bytes reg,1 2 2 3 2 mem,1 15+EA 7 7 2-4 (W88=23+EA) reg,CL 8+4n 5+n 3 2 mem,CL 20+EA+4n 8+n 7 2-4 (W88=28+EA+4n) reg,immed8 - 5+n 3 3 mem,immed8 - 8+n 7 3-5 - see EA for calculation of Effective Address "EA" :sar ^SAR - Shift Arithmetic Right Usage: SAR dest,count Modifies flags: CF OF PF SF ZF (AF undefined) Shifts the destination right by "count" bits with the current sign bit replicated in the leftmost bit. The Carry Flag contains the last bit shifted out. % Clocks Size %Operands 86/88 286 386 # Bytes reg,1 2 2 3 2 mem,1 15+EA 7 7 2-4 (W88=23+EA) reg,CL 8+4n 5+n 3 2 mem,CL 20+EA+4n 8+n 7 2-4 (W88=28+EA+4n) reg,immed8 - 5+n 3 3 mem,immed8 - 8+n 7 3-5 - see EA for calculation of Effective Address "EA" :sbb ^SBB - Subtract with Borrow Usage: SBB dest,src Modifies flags: AF CF OF PF SF ZF Subtracts the source from the destination, and subtracts 1 extra if the Carry Flag is set. Results are returned in "dest". % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 3 2 2 2 mem,reg 16+EA 7 6 2-4 (W88=24+EA) reg,mem 9+EA 7 7 2-4 (W88=13+EA) reg,immed 4 3 2 3-4 mem,immed 17+EA 7 7 3-6 (W88=25+EA) accum,immed 4 3 2 2-3 - see EA for calculation of Effective Address "EA" :scas:scasb:scasw:scasd ^SCAS - Scan String (Byte, Word or Doubleword) Usage: SCAS string SCASB SCASW SCASD (386) Modifies flags: AF CF OF PF SF ZF Compares value at ES:DI (even if operand is specified) from the accumulator and sets the flags similar to a subtraction. DI is incremented/decremented based on the instruction format (or operand size) and the state of the Direction Flag. Use with REP prefixes. % Clocks Size %Operands 86/88 286 386 # Bytes string 15 7 7 1 (W88=19) :setae:setnb ^SETAE/SETNB - Set if Above or Equal / Set if Not Below ^(unsigned, 386) Usage: SETAE dest SETNB dest Modifies flags: none Sets the byte in the operand to 1 if the Carry Flag is clear otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setb:setnae ^SETB/SETNAE - Set if Below / Set if Not Above or Equal ^(unsigned, 386) Usage: SETB dest SETNAE dest Modifies flags: none Sets the byte in the operand to 1 if the Carry Flag is set otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setbe:setna ^SETBE/SETNA - Set if Below or Equal / Set if Not Above ^(unsigned, 386) Usage: SETBE dest SETNA dest Modifies flags: none Sets the byte in the operand to 1 if the Carry Flag or the Zero Flag is set, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :sete:setz ^SETE/SETZ - Set if Equal / Set if Zero (386) Usage: SETE dest SETZ dest Modifies flags: none Sets the byte in the operand to 1 if the Zero Flag is set, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setne:setnz ^SETNE/SETNZ - Set if Not Equal / Set if Not Zero (386) Usage: SETNE dest SETNZ dest Modifies flags: none Sets the byte in the operand to 1 if the Zero Flag is clear, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setl:setnge ^SETL/SETNGE - Set if Less / Set if Not Greater or Equal ^(signed, 386) Usage: SETL dest SETNGE dest Modifies flags: none Sets the byte in the operand to 1 if the Sign Flag is not equal to the Overflow Flag, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setge:setnl ^SETGE/SETNL - Set if Greater or Equal / Set if Not Less ^(signed, 386) Usage: SETGE dest SETNL dest Modifies flags: none Sets the byte in the operand to 1 if the Sign Flag equals the Overflow Flag, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setle:setng ^SETLE/SETNG - Set if Less or Equal / Set if Not greater or Equal ^(signed, 386) Usage: SETLE dest SETNG dest Modifies flags: none Sets the byte in the operand to 1 if the Zero Flag is set or the Sign Flag is not equal to the Overflow Flag, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setg:setnle ^SETG/SETNLE - Set if Greater / Set if Not Less or Equal ^(signed, 386) Usage: SETG dest SETNLE dest Modifies flags: none Sets the byte in the operand to 1 if the Zero Flag is clear or the Sign Flag equals to the Overflow Flag, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :sets ^SETS - Set if Signed (386) Usage: SETS dest Modifies flags: none Sets the byte in the operand to 1 if the Sign Flag is set, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setns ^SETNS - Set if Not Signed (386) Usage: SETNS dest Modifies flags: none Sets the byte in the operand to 1 if the Sign Flag is clear, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setc ^SETC - Set if Carry (386) Usage: SETC dest Modifies flags: none Sets the byte in the operand to 1 if the Carry Flag is set, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setnc ^SETNC - Set if Not Carry (386) Usage: SETNC dest Modifies flags: none Sets the byte in the operand to 1 if the Carry Flag is clear, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :seto ^SETO - Set if Overflow (386) Usage: SETO dest Modifies flags: none Sets the byte in the operand to 1 if the Overflow Flag is set, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setno ^SETNO - Set if Not Overflow (386) Usage: SETNO dest Modifies flags: none Sets the byte in the operand to 1 if the Overflow Flag is clear, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setp:setpe ^SETP/SETPE - Set if Parity / Set if Parity Even (386) Usage: SETP dest SETPE dest Modifies flags: none Sets the byte in the operand to 1 if the Parity Flag is set, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :setnp:setpo ^SETNP/SETPO - Set if No Parity / Set if Parity Odd (386) Usage: SETNP dest SETPO dest Modifies flags: none Sets the byte in the operand to 1 if the Parity Flag is clear, otherwise sets the operand to 0. % Clocks Size %Operands 86/88 286 386 # Bytes reg8 - - 4 3 mem8 - - 5 3 :sgdt ^SGDT - Store Global Descriptor Table (286/386 privileged) Usage: SGDT dest Modifies flags: none Stores the Global Descriptor Table Register into the specified operand. % Clocks Size %Operands 86/88 286 386 # Bytes mem64 - 11 9 5 - see GDT :sidt ^SIDT - Store Interrupt Descriptor Table (286/386 privileged) Usage: SIDT dest Modifies flags: none Stores the Interrupt Descriptor Table Register into the specified operand. % Clocks Size %Operands 86/88 286 386 # Bytes mem64 - 12 9 5 :sldt ^SLDT - Store Local Descriptor Table (286/386 privileged) Usage: SLDT dest Modifies flags: none Stores the Local Descriptor Table Register into the specified operand. % Clocks Size %Operands 86/88 286 386 # Bytes reg16 - 2 2 3 mem16 - 2 2 5 :shr ^SHR - Shift Logical Right Usage: SHR dest,count Modifies flags: CF OF PF SF ZF (AF undefined) Shifts the destination right by "count" bits with zeroes shifted in on the left. The Carry Flag contains the last bit shifted out. % Clocks Size %Operands 86/88 286 386 # Bytes reg,1 2 2 3 2 mem,1 15+EA 7 7 2-4 (W88=23+EA) reg,CL 8+4n 5+n 3 2 mem,CL 20+EA+4n 8+n 7 2-4 (W88=28+EA+4n) reg,immed8 - 5+n 3 3 mem,immed8 - 8+n 7 3-5 - see EA for calculation of Effective Address "EA" :shld:shrd ^SHLD/SHRD - Double Precision Shift (386) Usage: SHLD dest,src,count SHRD dest,src,count Modifies flags: CF PF SF ZF (OF,AF undefined) SHLD shifts "dest" to the left "count" times and the bit positions opened are filled with the most significant bits of "src". SHRD shifts "dest" to the right "count" times and the bit positions opened are filled with the least significant bits of the second operand. Only the 5 lower bits of "count" are used. % Clocks Size %Operands 86/88 286 386 # Bytes reg16,reg16,immed8 - - 3 4 reg32,reg32,immed8 - - 3 4 mem16,reg16,immed8 - - 7 6 mem32,reg32,immed8 - - 7 6 reg16,reg16,CL - - 3 3 reg32,reg32,CL - - 3 3 mem16,reg16,CL - - 7 5 mem32,reg32,CL - - 7 5 :smsw ^SMSW - Store Machine Status Word (286/386 privileged) Usage: SMSW dest Modifies flags: none Store Machine Status Word into "dest". % Clocks Size %Operands 86/88 286 386 # Bytes reg16 - 2 10 3 mem16 - 3 3 5 - see MSW :stc ^STC - Set Carry Usage: STC Modifies flags: CF Sets the Carry Flag to 1. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 2 1 :std ^STD - Set Direction Flag Usage: STD Modifies flags: DF Sets the Direction Flag to 1 causing string instructions to auto-decrement SI and DI instead of auto-increment. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 2 1 :sti ^STI - Set Interrupt Flag (Enable Interrupts) Usage: STI Modifies flags: IF Sets the Interrupt Flag to 1, enabling recognition of all CPU hardware interrupts. % Clocks Size %Operands 86/88 286 386 # Bytes none 2 2 2 1 :stos:stosb:stosw:stosd ^STOS - Store String (Byte, Word or Doubleword) Usage: STOS dest STOSB STOSW STOSD Modifies flags: None Stores value in accumulator to location at ES:DI (even if operand is given). (E)DI is incremented/decremented based on the size of the operand (or instruction format) and the state of the Direction Flag. Use with REP prefixes. % Clocks Size %Operands 86/88 286 386 # Bytes dest 11 3 4 1 (W88=15) :str ^STR - Store Task Register (286/386 privileged) Usage: STR dest Modifies flags: None Stores the current Task Register to the specified operand. % Clocks Size %Operands 86/88 286 386 # Bytes reg16 - 2 2 3 mem16 - 3 2 5 :sub ^SUB - Subtract Usage: SUB dest,src Modifies flags: AF CF OF PF SF ZF The source is subtracted from the destination and the result is stored in the destination. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 3 2 2 2 mem,reg 16+EA 7 6 2-4 (W88=24+EA) reg,mem 9+EA 7 7 2-4 (W88=13+EA) reg,immed 4 3 2 3-4 mem,immed 17+EA 7 7 3-6 (W88=25+EA) accum,immed 4 3 2 2-3 - see EA for calculation of Effective Address "EA" :test ^TEST - Test For Bit Pattern Usage: TEST dest,src Modifies flags: CF OF PF SF ZF (AF undefined) Performs a logical AND of the two operands updating the flags register without saving the result. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 3 2 1 2 reg,mem 9+EA 6 5 2-4 (W88=13+EA) mem,reg 9+EA 6 5 2-4 (W88=13+EA) reg,immed 5 3 2 3-4 mem,immed 11+EA 6 5 3-6 accum,immed 4 3 2 2-3 - see EA for calculation of Effective Address "EA" :verr ^VERR - Verify Read (286/386 protected) Usage: VERR src Modifies flags: ZF Verifies the specified segment selector is valid and is readable at the current privilege level. If the segment is readable, the Zero Flag is set, otherwise it is cleared. % Clocks Size %Operands 86/88 286 386 # Bytes reg16 - 14 10 3 mem16 - 16 11 5 :verw ^VERW - Verify Write (286/386 protected) Usage: VERW src Modifies flags: ZF Verifies the specified segment selector is valid and is ratable at the current privilege level. If the segment is writable, the Zero Flag is set, otherwise it is cleared. % Clocks Size %Operands 86/88 286 386 # Bytes reg16 - 14 15 3 mem16 - 16 16 5 :wait:fwait ^WAIT/FWAIT - Event Wait Usage: WAIT FWAIT Modifies flags: None CPU enters wait state until the coprocessor signals it has finished it's operation. This instruction is used to prevent the CPU from accessing memory that may be temporarily in use by the coprocessor. WAIT and FWAIT are identical. % Clocks Size %Operands 86/88 286 386 # Bytes none 4 3 6 1 :xchg ^XCHG - Exchange Usage: XCHG dest,src Modifies flags: None Exchanges contents of source and destination. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 4 3 3 2 mem,reg 17+EA 5 5 2-4 (W88=25+EA) reg,mem 17+EA 5 5 2-4 (W88=25+EA) accum,reg 3 3 3 1 reg,accum 3 3 3 1 - see EA for calculation of Effective Address "EA" :xlat:xlatb ^XLAT/XLATB - Translate Usage: XLAT translation-table XLATB (masm 5.x) Modifies flags: None Replaces the byte in AL with byte from a user table addressed by BX by using the original AL as the index into the translate table. % Clocks Size %Operands 86/88 286 386 # Bytes table 11 5 5 1 :xor ^XOR - Exclusive OR Usage: XOR dest,src Modifies flags: CF OF PF SF ZF (AF undefined) Performs a bitwise exclusive OR of the two operands and returns the result in the destination. % Clocks Size %Operands 86/88 286 386 # Bytes reg,reg 3 2 2 2 mem,reg 16+EA 7 6 2-4 (W88=24+EA) reg,mem 9+EA 7 7 2-4 (W88=13+EA) reg,immed 4 3 2 3-4 mem,immed 17+EA 7 7 3-6 (W88=25+EA) accum,immed 4 3 2 2-3 - see EA for calculation of Effective Address "EA"