IDIV - IRETD instructions

IDIV - Signed Integer Division

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
operands	286	386	486	Size Bytes
reg8	17	19	19	2
reg16	25	27	27	2
reg32		43	43	2
mem8	20	22	20	2-4
mem16	38	30	28	2-4
mem32		46	44	2-4

IMUL - Signed Multiply

Usage: IMUL src
           IMUL src,immed (286+)
           IMUL dest,src,immed8 (286+)
           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 variations of this instruction allow specification of source and destination registers as well as a third immediate factor.

	Clocks
operands	286	386	486	Size Bytes
reg8	13	9-14	13-18	2
reg16	21	9-22	13-26	2
reg32		9-38	12-42	2
mem8	16	12-17	13-18	2-4
mem16	24	12-25	13-26	2-4
mem32		12-41	13-42	2-4
reg16,reg16		9-22	13-26	3-5
reg32,reg32		9-38	13-42	3-5
reg16,mem16		12-25	13-26	3-5
reg16,immed	21	9-22	13-26	3
reg32,immed	21	9-38	13-42	3-6
reg16,reg16,immed	2	9-22	13-26	3-6
reg32,reg32,immed	21	9-38	13-42	3-6
reg16,mem16,immed	24	12-25	13-26	3-6
reg32,mem32,immed	24	12-41	13-42	3-6

IN - Input Byte or Word From Port

Usage: IN accum,port

Modifies Flags: None

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.

	Clocks
operands	286	386	486	Size Bytes
accum,immed8	5	12	14	2
accum,immed8 (PM)		6/26	8/28/27	2
accum,DX	5	13	14	1
accum,DX (PM)		7/27	8/28/27	1
386+ protected mode timings depend on privilege levels. first number is the timing if: CPL <= IOPL second number is the timing if: CPL > IOPL or in VM 86 mode (386) CPL >= IOPL (486) third number is the timing when: virtual mode on 486 processor 486 virtual mode always requires 27 cycles

INC - Increment

Usage: INC dest

Modifies Flags: AF OF PF SF ZF

Adds one to destination unsigned binary operand.

	Clocks
operands	286	386	486	Size Bytes
reg8	2	2	1	2
reg16	2	2	1	1
reg32	2	2	1	1
mem	7	6	3	2-4

INS - Input String from Port (80188+)

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
operands	286	386	486	Size Bytes
dest,port	15	7	1	1
dest,port (PM)	5	9/29	10/32/30	1
none	5	15	17	1
none (PM)	5	9/29	10/32/30	1
386+ protected mode timings depend on privilege levels. first number is the timing if: CPL <= IOPL second number is the timing if: CPL > IOPL third number is the timing if: virtual mode on 486 processor

INT - Interrupt

Usage: INT num

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
operands	286	386	486	Size Bytes
3 (constant)	23+m	33	26	2
3 (prot. mode, same priv.)	40+m	59	44	2
3 (prot. mode, more priv.)	78+m	99	71	2
3 (from VM86 to PL 0)		119	82	2
3 (prot. mode via task gate)	167+m	TS	37+TS	2
immed8	23+m	37	30	1
immed8 (prot. mode, same priv.)	40+m	59	44	1
immed8 (prot. mode, more priv.)	78+m	99	71	1
immed8 (from VM86 to PL 0)		119	86	1
immed8 (prot. mode, via task gate)	167+m	TS	37+TS	1

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
operands	286	386	486	Size Bytes
none: jump	24+m	35	28	1
none: no jump	3	3	3	1
none: (prot. mode, same priv.)		59	46	1
none: (prot. mode, more priv.)		99	73	1
none: (from VM86 to PL 0)		84	119	1
none: (prot. mode, via task gate)		TS	39+TS	1

INVD - Invalidate Cache (486+)

Usage: INVD

Modifies Flags: None

Flushes CPU internal cache. Issues special function bus cycle which indicates to flush external caches. Data in write-back external caches is lost.

	Clocks
operands	286	386	486	Size Bytes
none			4	2

INVLPG - Invalidate Translation Look-Aside Buffer Entry (486+)

Usage: INVLPG

Modifies Flags: None

Invalidates a single page table entry in the Translation Look-Aside Buffer. Intel warns that this instruction may be implemented differently on future processors.

	Clocks
operands	286	386	486	Size Bytes
none			12	2
timing is for TLB entry hit only.

IRET/IRETD - Interrupt Return

Usage: IRET
IRETD (386+)

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
operands	286	386	486	Size Bytes
(iret)none	17+m	22	15	1
(prot. mode)	31+m	38	15	1
(to less privilege)	55+m	82	36	1
(different task, NT=1)	169+m	TS	TS+32	1
(iretd)		22/38	15	1
(to less privilege)		82	36	1
(to VM86 mode)		60	15	1
iretd (different task, NT=1)		TS	TS+32	1
386 timings are listed as real-mode/protected mode

[ TOC | Previous | NeXt | Winston's page ]