https://wiki.nox-rhea.org/ Mon, 27 Apr 2026 10:04:56 +0000 FeedCreator 1.8 https://wiki.nox-rhea.org/_media/wiki/dokuwiki.svg https://wiki.nox-rhea.org/ https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/aaa?rev=1677883987&do=diff AAA AAA - Ascii Adjust for Addition Changes contents of AL to valid unpacked decimal. The high order nibble is zeroed. Usage: AAA ; Modifies flags: CF AF (OF PF SF ZF SF undetermined) 286+ only 386+ only Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/aad?rev=1677883987&do=diff AAD AAD - Ascii Adjust for Division Descr. Usage: AAD ; Modifies flags: SF ZF PF (AF,CF,OF undefined) 286+ only 386+ only Clocks Size Operands 808x 286 386 486 Bytes anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/aam?rev=1677883987&do=diff AAM AAM - Ascii Adjust for Multiplication 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. This instruction is also known to have an undocumented behavior. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/aas?rev=1677883987&do=diff AAS AAS - Ascii Adjust for Subtraction Corrects result of a previous unpacked decimal subtraction in AL. High order nibble is zeroed. Usage: AAS ; Modifies flags: AF CF Clocks Size Operands anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/adc?rev=1677883987&do=diff ADC ADC - Add With Carry Sums two binary operands placing the result in the destination. If CF is set, a 1 is added to the destination. Usage: ADC Dest,Src Modifies flags: AF CF OF SF PF ZF 286+ only 386+ only Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/add?rev=1677883987&do=diff ADD ADD - Arithmetic Addition Adds “src” to “dest” and replacing the original contents of “dest”. Both operands are binary. Usage: ADD Dest,Src Modifies flags: AF CF OF SF PF ZF 286+ only 386+ only Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/and?rev=1677883987&do=diff AND AND - Logical And Performs a logical AND of the two operands replacing the destination with the result. Usage: AND dest,src Modifies flags: CF PF AF ZF SF OF AF undefined Clocks Size anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/arpl?rev=1677883987&do=diff ARPL (286+ protected mode) ARPL - Adjusted Requested Privilege Level of Selector 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/bound?rev=1677883987&do=diff BOUND - (80188+) BOUND - Array Index Bound Check 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/bsf?rev=1677883987&do=diff BSF - (386+ only) BSF - Bit Scan Forward (386+ only) 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). anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/bsr?rev=1677883987&do=diff BSR - (386+ only) BSR - Bit Scan Reverse (386+ only) 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). anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/bswap?rev=1677883987&do=diff BSWAP - (486+ only) BSWAP - Byte Swap (486+ only) Changes the byte order of a 32 bit register from big endian to little endian or vice versa. Result left in destination register is undefined if the operand is a 16 bit register. Usage: BSWAP reg32 ; anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/bt?rev=1677883987&do=diff BT - (386+ only) BT - Bit Test The destination bit indexed by the source value is copied into the Carry Flag. Usage: BT dest,src ; Modifies flags: CF Clocks Size Operands 808x 286 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/btc?rev=1677883987&do=diff BTC - (386+ only) BTC - Bit Test with Compliment The destination bit indexed by the source value is copied into the Carry Flag after being complimented (inverted). Usage: BTC dest,src ; Modifies flags: CF Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/btr?rev=1677883987&do=diff BTR - (386+ only) BTR - Bit Test with Reset The destination bit indexed by the source value is copied into the Carry Flag and then cleared in the destination. Usage: BTR dest,src ; Modifies flags: CF Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/bts?rev=1677883987&do=diff BTS - (386+ only) BTS - Bit Test and Set The destination bit indexed by the source value is copied into the Carry Flag and then set in the destination. Usage: BTS dest,src ; Modifies flags: CF Clocks Size anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/call?rev=1677883987&do=diff CALL CALL - Procedure Call 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. Usage: CALL destination ; anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/cbw?rev=1677883987&do=diff CBW CBW - Convert Byte to Word Converts byte in AL to word Value in AX by extending sign of AL throughout register AH. Usage: CBW ; Modifies flags: none Clocks Size Operands 808x anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/cdq?rev=1677883987&do=diff CDQ - (386+ only) CDQ - Convert Double to Quad Converts signed DWORD in EAX to a signed quad word in EDX:EAX by extending the high order bit of EAX throughout EDX Usage: CDQ ; Modifies flags: none Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/clts?rev=1677883987&do=diff CLTS - (286+ privileged) CLTS - Clear Task Switched Flag Clears the Task Switched Flag in the Machine Status Register. This is a privileged operation and is generally used only by operating system code. Usage: INSTR ; Modifies flags: none anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/clx-stx?rev=1677883987&do=diff CLx / STx Carry Flag CLC - Clear Carry Flag Clears the Carry Flag. Usage: CLC Modifies flags: CF Clocks Size Operands 808x 286 386 486 Bytes none 2 2 2 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/clx?rev=1677883987&do=diff CLx anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/cmc?rev=1677883987&do=diff CMC CMC - Complement Carry Flag Toggles (inverts) the Carry Flag Usage: CMC ; Modifies flags: CF Clocks Size Operands 808x 286 386 486 Bytes none 2 2 2 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/cmp?rev=1677883987&do=diff CMP - CMPS - CMPSB - CMPSD - CMPSW - CMPSCHG CMP - Compare Subtracts source from destination and updates the flags but does not save result. Flags can subsequently be checked for conditions. Usage: CMP dest,src Modifies flags: CF PF AF ZF SF OF anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/cwd?rev=1677883987&do=diff CWD CWD - Convert Word to Doubleword Extends sign of word in register AX throughout register DX forming a doubleword quantity in DX:AX. Usage: CWD ; Modifies flags: none Clocks Size Operands 808x anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/cwde?rev=1677883987&do=diff CWDE - (386+ only) CWDE - Convert Word to Extended Doubleword Converts a signed word in AX to a signed doubleword in EAX by extending the sign bit of AX throughout EAX. Usage: CWDE ; Modifies flags: none Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/daa?rev=1677883987&do=diff DAA DAA - Decimal Adjust for Addition Corrects result (in AL) of a previous BCD addition operation. Contents of AL are changed to a pair of packed decimal digits. Usage: DAA ; Modifies flags: AF CF PF SF ZF (OF undefined) Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/das?rev=1677883987&do=diff DAS DAS - Decimal Adjust for Subtraction Corrects result (in AL) of a previous BCD subtraction operation. Contents of AL are changed to a pair of packed decimal digits. Usage: DAS ; Modifies flags: AF CF PF SF ZF (OF undefined) anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/dec?rev=1677883987&do=diff DEC DEC - Decrement Unsigned binary subtraction of one from the destination. Usage: DEC dest ; Modifies flags: AF OF PF SF ZF Clocks Size Operands 808x 286 386 486 Bytes reg8 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/div?rev=1677883987&do=diff DIV DIV - Divide 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 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/enter?rev=1677883987&do=diff ENTER - (80188+) ENTER - Make Stack Frame 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 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/esc?rev=1677883987&do=diff ESC ESC - Escape Provides access to the data bus for other resident processors. The CPU treats it as a NOP but places memory operand on bus. Usage: ESC immed,src ; Modifies flags: none Clocks Size Operands anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/hlt?rev=1677883987&do=diff HLT HLT - Halt CPU Halts CPU until RESET line is activated, NMI or maskable interrupt received. The CPU becomes dormant but retains the current CS:IP for later restart. Usage: HLT ; Modifies flags: none Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/idiv?rev=1677883987&do=diff IDIV IDIV - Signed Integer Division 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 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/imul?rev=1677883987&do=diff IMUL IMUL - Signed Multiply 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/in?rev=1677884159&do=diff IN IN - Input Byte or Word From Port A byte, word or dword is read from “port” and placed in AL, AX or EAX 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/inc?rev=1677883987&do=diff INC INC - Increment dds one to destination unsigned binary operand. Usage: INC dest ; Modifies flags: AF OF PF SF ZF Clocks Size Operands 808x 286 386 486 Bytes anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:53:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/ins?rev=1677244596&do=diff INS - INSB - INSW - INSD INS - Input String from Port (80186+) 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. anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/int?rev=1677884159&do=diff INT INT - Interrupt 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 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/into?rev=1677884159&do=diff INTO INTO - Interrupt on Overflow If the Overflow Flag is set this instruction generates an INT 4 which causes the code addressed by 0000:0010 to be executed. Usage: INTO ; Modifies flags: TF IF Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/iret?rev=1677884159&do=diff IRET IRET/IRETD - Interrupt Return 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/ja-jnbe?rev=1677245466&do=diff JA-JNBE JA/JNBE - Jump Above / Jump Not Below or Equal Causes execution to branch to “label” if the Carry Flag and Zero Flag are both set. * Uses unsigned comparison. Usage: JA destination ; JNBE destination ; Jump ? Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:31:06 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jae-jnb?rev=1677863219&do=diff JAE-JNB JAE/JNB - Jump Above or Equal / Jump on Not Below Causes execution to branch to “label” if the Carry Flag is set. * Functionally similar to JNC * Uses unsigned comparison. Usage: JAE destination ; JNB destination ; anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:06:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jb-jnae?rev=1677245744&do=diff JB-JNAE JB/JNAE - Jump Below / Jump Not Above or Equal Causes execution to branch to “label” if the Carry Flag is set. * Functionally similar to JC * Uses unsigned comparison. Usage: JB destination ; JNAE destination ; Jump ? anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:35:44 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jbe-jna?rev=1677863917&do=diff JBE-JNA JBE/JNA - Jump Below or Equal / Jump Not Above Causes execution to branch to “label” if the Carry Flag or the Zero Flag is set. * unsigned comparison Usage: JBE destination ; JNA destination ; Jump ? Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:18:37 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jc?rev=1677245731&do=diff JC JC - Jump on Carry Causes execution to branch to “label” if the Carry Flag is set. * Functionally similar to JB and JNAE * Uses unsigned comparison. Usage: JBE destination ; JNA destination ; Jump ? Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:35:31 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jcxz?rev=1677863179&do=diff JCXZ-JECXZ JCXZ/JECXZ - Jump if Register (E)CX is Zero Causes execution to branch to “label” if register CX is zero. * Uses unsigned comparaison. Usage: JCXZ destination ; JECXZ destination ; 386+ only Jump ? Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:06:19 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/je-jz?rev=1677864996&do=diff JE-JZ JE/JZ - Jump Equal / Jump Zero Causes execution to branch to “label” if the Zero Flag is set. * unsigned comparison Usage: JE destination ; JZ destination ; Jump ? Clocks Size Operands anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:36:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jg-jnle?rev=1677245858&do=diff JG-JNLE JG/JNLE - Jump Greater / Jump Not Less or Equal Causes execution to branch to “label” if the Zerro Flag is Clear or the Sign Flag equal OverFlow Flag. * Uses Signed comparison. Usage: JG destination ; JNLE destination ; anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:37:38 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jge-jnl?rev=1677863830&do=diff JGE/JNL JGE/JNL - Jump Greater or Equal / Jump Not Less Causes execution to branch to “label” if the Sign Flag equals the Overflow Flag. * Signed comparison. Usage: JGE destination ; JNL destination ; Jump ? Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:17:10 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jl-jnge?rev=1677863971&do=diff JL/JNGE JL/JNGE - Jump Less / Jump Not Greater or Equal Causes execution to branch to “label” if the Sign Flag is not equal to Overflow Flag. * unsigned comparison Usage: JL destination ; JNGE destination ; Jump ? Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:19:31 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jle-jng?rev=1677864326&do=diff JLE/JNG JLE/JNG - Jump Less or Equal / Jump Not Greater Causes execution to branch to “label” if the Zero Flag is set or the Sign Flag is not equal to the Overflow Flag. * signed comparison Usage: JLE destination ; JNG destination ; anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:25:26 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jmp?rev=1677244596&do=diff JMP JMP - Unconditional Jump 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. anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jnc?rev=1677863388&do=diff JNC JNC - Jump If Not Carry Causes execution to branch to “label” if the Carry Flag is set. * Functionally similar to JAE & JNB * unsigned comparison Usage: JNC destination ; Jump ? Clocks Size Operands anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:09:48 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jne-jnz?rev=1677865035&do=diff JNE-JNZ JNE/JNZ - Jump Not Equal / Jump Not Zero Causes execution to branch to “label” if the Zero Flag is clear. * unsigned comparison Usage: JNE destination ; JNZ destination ; Jump ? Clocks Size anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:37:15 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jno?rev=1677865245&do=diff JNO JNO - Jump Not Overflow Causes execution to branch to “label” if the Overflow Flag is clear. * signed comparison Usage: JNO destination ; Jump ? Clocks Size Operands 808x anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:40:45 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jnp-jpo?rev=1677865541&do=diff JNP-JPO JNP-JPO - Jump Not Parity / Jump Parity Odd Causes execution to branch to “label” if the Parity Flag is clear. * unsigned comparison Usage: JNP destination ; JPO destination ; Jump ? Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:45:41 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jns?rev=1677865781&do=diff JNS JNS - Jump Not Signed Causes execution to branch to “label” if the Sign Flag is clear. * signed comparison Usage: JNS destination ; Jump ? Clocks Size Operands 808x 286 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:49:41 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jo?rev=1677865865&do=diff JO JO - Jump On Overflow Causes execution to branch to “label” if the Overflow Flag is set. * signed comparison Usage: JO destination ; Jump ? Clocks Size Operands 808x 286 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:51:05 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/jp-jpe?rev=1677866138&do=diff JP-JPE JP/JPE - Jump on Parity / Jump on Parity Even Causes execution to branch to “label” if the Parity Flag is set. * unsigned comparison Usage: JP destination ; JPE destination ; Jump ? Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:55:38 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/js?rev=1677866212&do=diff JS JS - Jump Signed Causes execution to branch to “label” if the Sign Flag is set. * signed comparison Usage: JS destination ; Jump ? Clocks Size Operands 808x 286 386 486 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 17:56:52 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lahf?rev=1677884159&do=diff LAHF LAHF - Load Register AH From Flags Copies bits 0-7 of the flags register into AH. This includes flags AF, CF, PF, SF and ZF other bits are undefined. Usage: LAHF ; Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lar?rev=1677884159&do=diff LAR LAR - Load Access Rights (286+ protected) 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lds?rev=1677244596&do=diff LDS LDS - Load Pointer Using DS 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. anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lea?rev=1677884159&do=diff LEA LEA - Load Effective Address Transfers offset address of “src” to the destination register. Usage: INSTR Dest,Src ; Modifies flags: none Clocks Size Operands 808x 286 anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/leave?rev=1677884159&do=diff LEAVE - (80188+) LEAVE - Restore Stack for Procedure Exit 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. Usage: LEAVE ; Modifies flags: anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/les?rev=1677244596&do=diff LES LES - Load Pointer Using ES 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. anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lfs?rev=1677866745&do=diff LFS - (386+) LFS - Load Pointer Using FS (386+ only) 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 18:05:45 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lgdt?rev=1677884159&do=diff LGDT (286+ privileged) LGDT - Load Global Descriptor Table (286+ privileged) Loads a value from an operand into the Global Descriptor Table (GDT) register. Usage: LGDT src ; Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lgs?rev=1677884159&do=diff LGS (386+) LGS - Load Pointer Using GS (386+ only) 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lidt?rev=1677884159&do=diff LIDT (286+ privileged) LIDT - Load Interrupt Descriptor Table (286+ privileged) Loads a value from an operand into the Interrupt Descriptor Table (IDT) register. Usage: LIDT src ; Modifies flags: none Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lldt?rev=1677884159&do=diff LLDT (286+ privileged) LLDT - Load Local Descriptor Table (286+ privileged) Loads a value from an operand into the Local Descriptor Table Register (LDTR). Usage: LLDT src ; Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lmsw?rev=1677884159&do=diff LMSW (286+ privileged) LMSW - Load Machine Status Word (286+ privileged) Loads the Machine Status Word (MSW) from data found at “src” Usage: LLDT src ; Modifies flags: none Clocks Size Operands anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lock?rev=1677884159&do=diff LOCK LOCK - Lock Bus 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lods?rev=1677244596&do=diff LODS - LODSB - LODSW - LODSD LODS - Load String (Byte, Word or Double) 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. anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/loop?rev=1677884159&do=diff LOOP LOOP - Decrement CX and Loop if CX Not Zero 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 Usage: LOOP label ; anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/loope-loopz?rev=1677884159&do=diff LOOPE-LOOPZ LOOPE/LOOPZ - Loop While Equal / Loop While Zero 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/loopne-loopnz?rev=1677884159&do=diff LOOPNE-LOOPNZ LOOPNE/LOOPNZ - Loop While Not Equal / Loop While Not Zero 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lsl?rev=1677883748&do=diff LSL (286+ protected) LSL - Load Segment Limit (286+ protected) 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:49:08 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/lss?rev=1677884350&do=diff LSS (386+ only) LSS - Load Pointer Using SS (386+ only) 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:59:10 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/ltr?rev=1677884490&do=diff LTR (286+ privileged) LTR - Load Task Register (286+ privileged) Loads the current task register with the value specified in “src”. Usage: LSL Dest,Src ; Modifies flags: none Clocks Size Operands anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:01:30 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/mov?rev=1677244596&do=diff MOV MOV - Move Byte, Word or DWord Copies byte, word or dword 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. anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/movs?rev=1677244596&do=diff MOVS - MOVSB - MOVSW - MOVSD MOVS - Move String (Byte, Word or DWord) 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 anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/movsx?rev=1677884681&do=diff MOVSX (386+ only) MOVSX - Move with Sign Extend (386+ only) Copies the value of the source operand to the destination register with the sign extended. Usage: MOVSX dest,src ; Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:04:41 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/movzx?rev=1677884738&do=diff MOVZX (386+ only) MOVZX - Move with Zero Extend (386+ only) Copies the value of the source operand to the destination register with the zeroes extended. Usage: MOVZX dest,src ; Modifies flags: none Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:05:38 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/mul?rev=1677244596&do=diff MUL MUL - unsigned Multiply 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 anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/neg?rev=1677884814&do=diff NEG NEG - Two's Complement Negation Subtracts the destination from 0 and saves the 2s complement of “dest” back into “dest”. Usage: NEG dest Modifies flags: AF CF OF PF SF ZF Clocks Size anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:06:54 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/nop?rev=1677244596&do=diff NOP NOP - No Operation This is a do nothing instruction. It results in occupation of both space and time and is most useful for patching code segments. Usage: NOP Modifies flags: None Clocks Size anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/not?rev=1677354679&do=diff NOT NOT - Logical Not Inverts the bits of the “dest” operand forming the 1s complement, also called “ One's Compliment Negation”. Usage: NOT dest Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Sat, 25 Feb 2023 19:51:19 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/or?rev=1677354616&do=diff OR OR - Logical Or 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. Usage: OR dest,src Modifies flags: CF PF AF ZF SF OF AF undefined anonymous@undisclosed.example.com (Anonymous) Sat, 25 Feb 2023 19:50:16 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/out?rev=1677884159&do=diff OUT OUT - Output Data to Port Transfers byte in AL,word in AX or dword in EAX 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 22:55:59 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/outs?rev=1677244596&do=diff OUTS - OUTSB - OUTSW - OUTSD INS - Output String from Port (80186+) 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. anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/pop?rev=1677885200&do=diff POP POP - Pop Word off Stack 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. Usage: POP dest Modifies flags: none Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:13:20 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/popa-popad?rev=1677885330&do=diff POPA - POPAD (80188+ only) POPA/POPAD - Pop All Registers onto Stack (80188+ only) 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. anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:15:30 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/popf?rev=1677884899&do=diff POPF POPF/POPD - Pop Flags off Stack Pops word/doubleword from stack into the Flags Register and then increments SP by 2 (for POPF) or 4 (for POPFD). Usage: POPF POPFD ; (386+ only) Modifies flags: CF PF AF ZF SF TF IF DF OF IOPL NT RF VM anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:08:19 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/push?rev=1677885537&do=diff PUSH PUSH - Push Word onto Stack 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). Usage: PUSH src PUSH immed ; (80188+ only) Modifies flags: none anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:18:57 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/pusha-pushad?rev=1769971592&do=diff PUSHA - PUSHAD (80188+ only) PUSHA/PUSHAD - Push All Registers onto Stack (80188+ only) Pushes all general purpose registers onto the stack in the following order: * (E)AX * (E)CX * (E)DX * (E)BX * (E)SP (see notes) * (E)BP * (E)SI anonymous@undisclosed.example.com (Anonymous) Sun, 01 Feb 2026 18:46:32 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/pushf?rev=1677884947&do=diff PUSHF PUSHF/PUSHFD - Push Flags onto Stack Transfers the Flags Register onto the stack. PUSHF saves a 16 bit value while PUSHFD saves a 32 bit value. Usage: PUSHF PUSHFD ; (386+ only) Modifies flags: None Clocks anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:09:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/rcl?rev=1677925886&do=diff RCL RCL - Rotate Through Carry Left 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. Usage: RCL dest,count Modifies flags: anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:31:26 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/rct?rev=1677886031&do=diff RCR RCR - Rotate Through Carry Right Rotates the bits in the destination to the left “count” times with all data pushed out the right side re-entering on the left. The Carry Flag holds the last bit rotated out. Usage: RCR dest,count Modifies flags: anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 23:27:11 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/rep?rev=1677244596&do=diff REP REP - Repeat String Operation Repeats execution of string instructions while CX != 0. After each string operation, CX is decremented and the Zero Flag is tested. Usage: REP MOVSB 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: anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/repe-repz?rev=1677244596&do=diff REPE-REPZ REPE/REPZ - Repeat Equal / Repeat Zero 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. anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/repne-repnz?rev=1677244596&do=diff REPNE-REPNZ REPNE/REPNZ - Repeat Not Equal / Repeat Not Zero 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. anonymous@undisclosed.example.com (Anonymous) Fri, 24 Feb 2023 13:16:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/ret?rev=1677925675&do=diff RET-RETF-RETN RET/RETF - Return From Procedure 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. anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:27:55 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/rol?rev=1677925904&do=diff ROL ROL - Rotate Left 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. Usage: ROL dest,count anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:31:44 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/ror?rev=1677925864&do=diff ROR ROR - Rotate Right 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. Usage: ROR dest,count anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:31:04 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sahf?rev=1677925984&do=diff SAHF SAHF - Store AH Register into Flags Transfers bits 0-7 of AH into the Flags Register. This includes AF, CF, PF, SF and ZF. Usage: SAHF ; Modifies flags: AF CF PF SF ZF Clocks Size Operands anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:33:04 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sal?rev=1731420067&do=diff SAL SAL - Shift Arithmetic Left Shifts the destination left by “count” bits with zeroes shifted in on right. The Carry Flag contains the last bit shifted out. Usage: SAL dest,count SHL dest,count Modifies flags: CF OF PF SF ZF (AF undefined) anonymous@undisclosed.example.com (Anonymous) Tue, 12 Nov 2024 14:01:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sar?rev=1677926259&do=diff SAR SAR - Shift Arithmetic Right 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. Usage: SAR dest,count Modifies flags: CF OF PF SF ZF (AF undefined) anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:37:39 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sbb?rev=1677926389&do=diff SBB SBB - Subtract with Borrow Subtracts the source from the destination, and subtracts 1 extra if the Carry Flag is set. Results are returned in “dest”. Usage: SBB Dest,Src Modifies flags: AF CF OF SF PF ZF 286+ only 386+ only anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:39:49 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/scas?rev=1677926770&do=diff SCAS SCAS - Scan String (Byte, Word or Doubleword) 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. anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:46:10 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/see-footer?rev=1709498717&do=diff * see Instructions list, Instruction Timing, 8086 Architecture, CPU anonymous@undisclosed.example.com (Anonymous) Sun, 03 Mar 2024 20:45:17 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setb-setnea?rev=1677927137&do=diff SETB/SETNAE (386+ only) SETB/SETNAE - Set if Below / Set if Not Above or Equal (unsigned, 386+ only) Sets the byte in the operand to 1 if the Carry Flag is set otherwise sets the operand to 0. Usage: SETB dest SETNAE dest Modifies flags: none anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:52:17 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setbe-setna?rev=1677927265&do=diff SETBE/SETNA (386+ only) SETBE/SETNA - Set if Below or Equal / Set if Not Above (unsigned, 386+ only) Sets the byte in the operand to 1 if the Carry Flag or the Zero Flag is set, otherwise sets the operand to 0. Usage: SETBE dest SETNA dest anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:54:25 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setc?rev=1677927399&do=diff SETC (386+ only) SETC - Set if Carry (386+ only) Sets the byte in the operand to 1 if the Carry Flag is set, otherwise sets the operand to 0. Usage: SETC dest Modifies flags: none Clocks Size Operands anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:56:39 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sete-setz?rev=1677927462&do=diff SETE-SETZ (386+ only) SETE/SETZ - Set if Equal / Set if Zero (386+ only) Sets the byte in the operand to 1 if the Zero Flag is set, otherwise sets the operand to 0. Usage: SETE dest SETZ dest Modifies flags: none Clocks anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:57:42 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setea-setnb?rev=1677927156&do=diff SETAE/SETNB (386+ only) SETAE/SETNB - Set if Above or Equal / Set if Not Below (unsigned, 386+ only) Sets the byte in the operand to 1 if the Carry Flag is clear otherwise sets the operand to 0. Usage: SETAE dest SETNB dest Modifies flags: anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 10:52:36 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setg-setnle?rev=1677927655&do=diff SETG/SETNLE (386+ only) SETG/SETNLE - Set if Greater / Set if Not Less or Equal (signed, 386+ only) 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. Usage: SETG dest SETNLE dest anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:00:55 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setge-setnl?rev=1677927732&do=diff SETGE/SETNL (386+ only) SETGE/SETNL - Set if Greater or Equal / Set if Not Less (signed, 386+ only) Sets the byte in the operand to 1 if the Sign Flag equals the Overflow Flag, otherwise sets the operand to 0. Usage: SETGE dest SETNL dest Modifies flags: anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:02:12 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setl-setnge?rev=1677927868&do=diff SETL/SETNGE (386+ only) SETL/SETNGE - Set if Less / Set if Not Greater or Equal (signed, 386+ only) 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. Usage: SETL dest SETNGE dest anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:04:28 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setle-setng?rev=1677928151&do=diff SETLE/SETNG (386+ only) SETLE/SETNG - Set if Less or Equal / Set if Not greater or Equal (signed, 386+ only) 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. anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:09:11 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setnc?rev=1677928266&do=diff SETNC (386+ only) SETNC - Set if Not Carry (386+ only) Sets the byte in the operand to 1 if the Carry Flag is clear, otherwise sets the operand to 0. Usage: SETNC dest Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:11:06 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setne-setnz?rev=1677928378&do=diff SETNE-SETNZ (386+ only) SETNE/SETNZ - Set if Not Equal / Set if Not Zero (386+ only) Sets the byte in the operand to 1 if the Zero Flag is clear, otherwise sets the operand to 0. Usage: SETNE dest SETNZ dest Modifies flags: none anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:12:58 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setno?rev=1677929045&do=diff SETNO (386+ only) SETNO - Set if Not Overflow (386+ only) Sets the byte in the operand to 1 if the Overflow Flag is clear, otherwise sets the operand to 0. Usage: SETNO dest Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:24:05 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setnp-setpo?rev=1677929107&do=diff SETNP-SETPO (386+ only) SETNP/SETPO - Set if No Parity / Set if Parity Odd (386+ only) Sets the byte in the operand to 1 if the Overflow Flag is clear, otherwise sets the operand to 0. Usage: SETNP dest SETPO dest Modifies flags: none anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:25:07 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setns?rev=1677929173&do=diff SETNS (386+ only) SETNS - Set if Not Signed (386+ only) Sets the byte in the operand to 1 if the Sign Flag is clear, otherwise sets the operand to 0. Usage: SETNS dest Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:26:13 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/seto?rev=1677929228&do=diff SETO (386+ only) SETO - Set if Overflow (386+ only) Sets the byte in the operand to 1 if the Overflow Flag is set, otherwise sets the operand to 0. Usage: SETO dest Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:27:08 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/setp-setpe?rev=1677929303&do=diff SETP-SETPE (386+ only) SETP/SETPE - Set if Parity / Set if Parity Even (386+ only) Sets the byte in the operand to 1 if the Parity Flag is set, otherwise sets the operand to 0. Usage: SETP dest SETPE dest Modifies flags: none Clocks anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:28:23 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sets?rev=1677929342&do=diff SETS (386+ only) SETS - Set if Signed (386+ only) Sets the byte in the operand to 1 if the Sign Flag is set, otherwise sets the operand to 0. Usage: SETS dest Modifies flags: none Clocks Size Operands anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:29:02 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sgdt?rev=1677931487&do=diff SGDT (286+ privileged) SGDT - Store Global Descriptor Table (286+ privileged) Stores the Global Descriptor Table (GDT) Register into the specified operand. Usage: SGDT dest Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 12:04:47 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/shl?rev=1731420097&do=diff SHL SHL - Shift Logical Left Shifts the destination left by “count” bits with zeroes shifted in on right. The Carry Flag contains the last bit shifted out. Usage: SAL dest,count SHL dest,count Modifies flags: CF OF PF SF ZF (AF undefined) anonymous@undisclosed.example.com (Anonymous) Tue, 12 Nov 2024 14:01:37 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/shld-shrd?rev=1771854534&do=diff SHLD-SHRD SHLD/SHRD - Double Precision Shift (386+ only) 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. anonymous@undisclosed.example.com (Anonymous) Mon, 23 Feb 2026 13:48:54 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/shr?rev=1677928551&do=diff SHR SHR - Shift Logical Right Shifts the destination right by “count” bits with zeroes shifted in on the left. The Carry Flag contains the last bit shifted out. Usage: SHR dest,count Modifies flags: CF OF PF SF ZF (AF undefined) anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:15:51 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sidt?rev=1677931474&do=diff SIDT (286+ privileged) SIDT - Store Interrupt Descriptor Table (286+ privileged) Stores the Interrupt Descriptor Table (IDT) Register into the specified operand. Usage: SIDT dest Modifies flags: none Clocks anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 12:04:34 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sldt?rev=1677931607&do=diff SLDT (286+ privileged) SLDT - Store Local Descriptor Table (286+ privileged) Stores the Local Descriptor Table (LDT) Register into the specified operand. Usage: SLDT dest Modifies flags: none Clocks Size anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 12:06:47 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/smsw?rev=1677931926&do=diff SMSW (286+ privileged) SMSW - Store Machine Status Word (286+ privileged) Store Machine Status Word (MSW) into “dest”. Usage: SMSW dest ; Modifies flags: none Clocks Size Operands 808x 286 anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 12:12:06 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/start?rev=1677867021&do=diff Instructions List * AAA * AAD * AAM * AAS * ADC * ADD * AND * ARPL (286+ protected mode) * BOUND - (80188+) * BSF - (386+ only) * BSR - (386+ only) * BSWAP - (486+ only) * BT - (386+ only) * BTC - (386+ only) * BTR - (386+ only) * BTS - (386+ only) * CALL * CBW * CDQ - (386+ only) * CLTS - (286+ privileged) * CLx * CLx / STx * CMC * CMP - CMPS - CMPSB - CMPSD - CMPSW - CMPSCHG * CWD * CWDE - (386+ only) * DAA * DAS * DEC * DIV * ENTER - (80188+) * ESC * HLT * … anonymous@undisclosed.example.com (Anonymous) Fri, 03 Mar 2023 18:10:21 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/stos?rev=1677928824&do=diff STOS - STOSB - STOSW - STOSD STOS - Store String (Byte, Word or Double) Stores value in accumulator to location at ES:(E)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. anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:20:24 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/str?rev=1677931889&do=diff STR (286+ privileged) STR - Store Task Register (286+ privileged) Stores the current Task Register to the specified operand. Usage: STR dest ; Modifies flags: none Clocks Size Operands 808x anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 12:11:29 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/stx?rev=1677354450&do=diff STx anonymous@undisclosed.example.com (Anonymous) Sat, 25 Feb 2023 19:47:30 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/sub?rev=1677930094&do=diff SUB SUB - Subtract The source is subtracted from the destination and the result is stored in the destination. Usage: SUB Dest,Src Modifies flags: AF CF OF SF PF ZF 286+ only 386+ only Clocks Size anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:41:34 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/test?rev=1677930417&do=diff TEST TEST - Test For Bit Pattern Performs a logical {AND} of the two operands updating the flags register without saving the result. Usage: TEST dest,src ; Modifies flags: CF OF PF SF ZF (AF undefined) Clocks anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 11:46:57 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/verr?rev=1677932144&do=diff VERR (286+ protected) VERR - Verify Read (286+ protected) 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. Usage: VERR src anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 12:15:44 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/verw?rev=1717511371&do=diff VERW (286+ protected) VERW - Verify Write (286+ protected) 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. Usage: VERW src anonymous@undisclosed.example.com (Anonymous) Tue, 04 Jun 2024 14:29:31 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/wait?rev=1677932331&do=diff WAIT-FWAIT WAIT/FWAIT - Event Wait 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. anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 12:18:51 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/xchg?rev=1677932582&do=diff XCHG XCHG - Exchange Exchanges contents of source and destination. Usage: XCHG dest,src ; Modifies flags: none Clocks Size Operands 808x 286 386 486 Bytes anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 12:23:02 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/xlat-xlatb?rev=1677932818&do=diff XLAT-XLATB XLAT/XLATB - Translate Replaces the byte in AL with byte from a user table addressed by BX. The original value of AL is the index into the translate table. Locates a byte entry in a table in memory, using the contents of the AL register as a table index, then copies the contents of the table entry back into the AL register. anonymous@undisclosed.example.com (Anonymous) Sat, 04 Mar 2023 12:26:58 +0000 https://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/instr/xor?rev=1677354658&do=diff XOR XOR- Exclusive Or Performs a bitwise exclusive OR of the operands and returns the result in the destination. Usage: XOR dest,src Modifies flags: CF PF AF ZF SF OF AF undefined Clocks Size anonymous@undisclosed.example.com (Anonymous) Sat, 25 Feb 2023 19:50:58 +0000