Complete 8086 instruction set
Quick reference:
Operand types:
REG: AX, BX, CX, DX, AH, AL, BL, BH, CH, CL, DH, DL, DI, SI, BP, SP.
SREG: DS, ES, SS, and only as second operand: CS.
memory: [BX], [BX+SI+7], variable, etc...(see Memory Access).
immediate: 5, -24, 3Fh, 10001101b, etc...
Notes:
These marks are used to show the state of the flags:
1 - instruction sets this flag to 1.
0 - instruction sets this flag to 0.
r - flag value depends on result of the instruction.
? - flag value is undefined (maybe 1 or 0).
Some instructions generate exactly the same machine code, so disassembler may have a problem decoding to your original code. This is especially important for Conditional Jump instructions (see "Program Flow Control" in Tutorials for more information).
Instructions in alphabetical order:
C Z S O P A popped JA label Short Jump if first operand is Above second operand (as set by CMP instruction). Unsigned.
Algorithm:
if (CF = 0) and (ZF = 0) then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 250 CMP AL, 5 JA label1 PRINT 'AL is not above 5' JMP exit label1: PRINT 'AL is above 5' exit: RET C Z S O P A unchanged JAE label Short Jump if first operand is Above or Equal to second operand (as set by CMP instruction). Unsigned.
Algorithm:
if CF = 0 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 5 CMP AL, 5 JAE label1 PRINT 'AL is not above or equal to 5' JMP exit label1: PRINT 'AL is above or equal to 5' exit: RET C Z S O P A unchanged JB label Short Jump if first operand is Below second operand (as set by CMP instruction). Unsigned.
Algorithm:
if CF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 1 CMP AL, 5 JB label1 PRINT 'AL is not below 5' JMP exit label1: PRINT 'AL is below 5' exit: RET C Z S O P A unchanged JBE label Short Jump if first operand is Below or Equal to second operand (as set by CMP instruction). Unsigned.
Algorithm:
if CF = 1 or ZF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 5 CMP AL, 5 JBE label1 PRINT 'AL is not below or equal to 5' JMP exit label1: PRINT 'AL is below or equal to 5' exit: RET C Z S O P A unchanged JC label Short Jump if Carry flag is set to 1.
Algorithm:
if CF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 255 ADD AL, 1 JC label1 PRINT 'no carry.' JMP exit label1: PRINT 'has carry.' exit: RET C Z S O P A unchanged JCXZ label Short Jump if CX register is 0.
Algorithm:
if CX = 0 then jump
Example: include 'emu8086.inc' ORG 100h MOV CX, 0 JCXZ label1 PRINT 'CX is not zero.' JMP exit label1: PRINT 'CX is zero.' exit: RET C Z S O P A unchanged JE label Short Jump if first operand is Equal to second operand (as set by CMP instruction). Signed/Unsigned.
Algorithm:
if ZF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 5 CMP AL, 5 JE label1 PRINT 'AL is not equal to 5.' JMP exit label1: PRINT 'AL is equal to 5.' exit: RET C Z S O P A unchanged JG label Short Jump if first operand is Greater then second operand (as set by CMP instruction). Signed.
Algorithm:
if (ZF = 0) and (SF = OF) then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 5 CMP AL, -5 JG label1 PRINT 'AL is not greater -5.' JMP exit label1: PRINT 'AL is greater -5.' exit: RET C Z S O P A unchanged JGE label Short Jump if first operand is Greater or Equal to second operand (as set by CMP instruction). Signed.
Algorithm:
if SF = OF then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, -5 JGE label1 PRINT 'AL < -5' JMP exit label1: PRINT 'AL >= -5' exit: RET C Z S O P A unchanged JL label Short Jump if first operand is Less then second operand (as set by CMP instruction). Signed.
Algorithm:
if SF <> OF then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, -2 CMP AL, 5 JL label1 PRINT 'AL >= 5.' JMP exit label1: PRINT 'AL < 5.' exit: RET C Z S O P A unchanged JLE label Short Jump if first operand is Less or Equal to second operand (as set by CMP instruction). Signed.
Algorithm:
if SF <> OF or ZF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, -2 CMP AL, 5 JLE label1 PRINT 'AL > 5.' JMP exit label1: PRINT 'AL <= 5.' exit: RET C Z S O P A unchanged JMP label
4-byte address
Unconditional Jump. Transfers control to another part of the program. 4-byte address may be entered in this form: 1234h:5678h, first value is a segment second value is an offset.
Algorithm:
always jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 5 JMP label1 ; jump over 2 lines! PRINT 'Not Jumped!' MOV AL, 0 label1: PRINT 'Got Here!' RET C Z S O P A unchanged JNA label Short Jump if first operand is Not Above second operand (as set by CMP instruction). Unsigned.
Algorithm:
if CF = 1 or ZF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, 5 JNA label1 PRINT 'AL is above 5.' JMP exit label1: PRINT 'AL is not above 5.' exit: RET C Z S O P A unchanged JNAE label Short Jump if first operand is Not Above and Not Equal to second operand (as set by CMP instruction). Unsigned.
Algorithm:
if CF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, 5 JNAE label1 PRINT 'AL >= 5.' JMP exit label1: PRINT 'AL < 5.' exit: RET C Z S O P A unchanged JNB label Short Jump if first operand is Not Below second operand (as set by CMP instruction). Unsigned.
Algorithm:
if CF = 0 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 7 CMP AL, 5 JNB label1 PRINT 'AL < 5.' JMP exit label1: PRINT 'AL >= 5.' exit: RET C Z S O P A unchanged JNBE label Short Jump if first operand is Not Below and Not Equal to second operand (as set by CMP instruction). Unsigned.
Algorithm:
if (CF = 0) and (ZF = 0) then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 7 CMP AL, 5 JNBE label1 PRINT 'AL <= 5.' JMP exit label1: PRINT 'AL > 5.' exit: RET C Z S O P A unchanged JNC label Short Jump if Carry flag is set to 0.
Algorithm:
if CF = 0 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 2 ADD AL, 3 JNC label1 PRINT 'has carry.' JMP exit label1: PRINT 'no carry.' exit: RET C Z S O P A unchanged JNE label Short Jump if first operand is Not Equal to second operand (as set by CMP instruction). Signed/Unsigned.
Algorithm:
if ZF = 0 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, 3 JNE label1 PRINT 'AL = 3.' JMP exit label1: PRINT 'Al <> 3.' exit: RET C Z S O P A unchanged JNG label Short Jump if first operand is Not Greater then second operand (as set by CMP instruction). Signed.
Algorithm:
if (ZF = 1) and (SF <> OF) then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, 3 JNG label1 PRINT 'AL > 3.' JMP exit label1: PRINT 'Al <= 3.' exit: RET C Z S O P A unchanged JNGE label Short Jump if first operand is Not Greater and Not Equal to second operand (as set by CMP instruction). Signed.
Algorithm:
if SF <> OF then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, 3 JNGE label1 PRINT 'AL >= 3.' JMP exit label1: PRINT 'Al < 3.' exit: RET C Z S O P A unchanged JNL label Short Jump if first operand is Not Less then second operand (as set by CMP instruction). Signed.
Algorithm:
if SF = OF then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, -3 JNL label1 PRINT 'AL < -3.' JMP exit label1: PRINT 'Al >= -3.' exit: RET C Z S O P A unchanged JNLE label Short Jump if first operand is Not Less and Not Equal to second operand (as set by CMP instruction). Signed.
Algorithm:
if (SF = OF) and (ZF = 0) then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, -3 JNLE label1 PRINT 'AL <= -3.' JMP exit label1: PRINT 'Al > -3.' exit: RET C Z S O P A unchanged JNO label Short Jump if Not Overflow.
Algorithm:
if OF = 0 then jump
Example: ; -5 - 2 = -7 (inside -128..127) ; the result of SUB is correct, ; so OF = 0: include 'emu8086.inc' ORG 100h MOV AL, -5 SUB AL, 2 ; AL = 0F9h (-7) JNO label1 PRINT 'overflow!' JMP exit label1: PRINT 'no overflow.' exit: RET C Z S O P A unchanged JNP label Short Jump if No Parity (odd). Only 8 low bits of result are checked. Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Algorithm:
if PF = 0 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 00000111b ; AL = 7 OR AL, 0 ; just set flags. JNP label1 PRINT 'parity even.' JMP exit label1: PRINT 'parity odd.' exit: RET C Z S O P A unchanged JNS label Short Jump if Not Signed (if positive). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Algorithm:
if SF = 0 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 00000111b ; AL = 7 OR AL, 0 ; just set flags. JNS label1 PRINT 'signed.' JMP exit label1: PRINT 'not signed.' exit: RET C Z S O P A unchanged JNZ label Short Jump if Not Zero (not equal). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Algorithm:
if ZF = 0 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 00000111b ; AL = 7 OR AL, 0 ; just set flags. JNZ label1 PRINT 'zero.' JMP exit label1: PRINT 'not zero.' exit: RET C Z S O P A unchanged JO label Short Jump if Overflow.
Algorithm:
if OF = 1 then jump
Example: ; -5 - 127 = -132 (not in -128..127) ; the result of SUB is wrong (124), ; so OF = 1 is set: include 'emu8086.inc' org 100h MOV AL, -5 SUB AL, 127 ; AL = 7Ch (124) JO label1 PRINT 'no overflow.' JMP exit label1: PRINT 'overflow!' exit: RET C Z S O P A unchanged JP label Short Jump if Parity (even). Only 8 low bits of result are checked. Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Algorithm:
if PF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 00000101b ; AL = 5 OR AL, 0 ; just set flags. JP label1 PRINT 'parity odd.' JMP exit label1: PRINT 'parity even.' exit: RET C Z S O P A unchanged JPE label Short Jump if Parity Even. Only 8 low bits of result are checked. Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Algorithm:
if PF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 00000101b ; AL = 5 OR AL, 0 ; just set flags. JPE label1 PRINT 'parity odd.' JMP exit label1: PRINT 'parity even.' exit: RET C Z S O P A unchanged JPO label Short Jump if Parity Odd. Only 8 low bits of result are checked. Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Algorithm:
if PF = 0 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 00000111b ; AL = 7 OR AL, 0 ; just set flags. JPO label1 PRINT 'parity even.' JMP exit label1: PRINT 'parity odd.' exit: RET C Z S O P A unchanged JS label Short Jump if Signed (if negative). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Algorithm:
if SF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 10000000b ; AL = -128 OR AL, 0 ; just set flags. JS label1 PRINT 'not signed.' JMP exit label1: PRINT 'signed.' exit: RET C Z S O P A unchanged JZ label Short Jump if Zero (equal). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Algorithm:
if ZF = 1 then jump
Example: include 'emu8086.inc' ORG 100h MOV AL, 5 CMP AL, 5 JZ label1 PRINT 'AL is not equal to 5.' JMP exit label1: PRINT 'AL is equal to 5.' exit: RET C Z S O P A unchanged LAHF No operands Load AH from 8 low bits of Flags register.
Algorithm:
AH = flags register
AH bit: 7 6 5 4 3 2 1 0 [SF] [ZF] [0] [AF] [0] [PF] [1] [CF] bits 1, 3, 5 are reserved.
C Z S O P A unchanged LDS REG, memory Load memory double word into word register and DS.
Algorithm:
Example: STC ; set carry (CF=1). MOV AL, 1Ch ; AL = 00011100b RCL AL, 1 ; AL = 00111001b, CF=0. RET C O r r OF=0 if first operand keeps original sign. RCR memory, immediate
REG, immediate
memory, CL
REG, CL Rotate operand1 right through Carry Flag. The number of rotates is set by operand2.
Algorithm:
shift all bits right, the bit that goes off is set to CF and previous value of CF is inserted to the left-most position.
Example: STC ; set carry (CF=1). MOV AL, 1Ch ; AL = 00011100b RCR AL, 1 ; AL = 10001110b, CF=0. RET C O r r OF=0 if first operand keeps original sign. REP chain instruction
Repeat following MOVSB, MOVSW, LODSB, LODSW, STOSB, STOSW instructions CX times.
Algorithm:
check_cx:
if CX <> 0 then
Example: MOV AL, 1Ch ; AL = 00011100b ROL AL, 1 ; AL = 00111000b, CF=0. RET C O r r OF=0 if first operand keeps original sign. ROR memory, immediate
REG, immediate
memory, CL
REG, CL Rotate operand1 right. The number of rotates is set by operand2.
Algorithm:
shift all bits right, the bit that goes off is set to CF and the same bit is inserted to the left-most position.
Example: MOV AL, 1Ch ; AL = 00011100b ROR AL, 1 ; AL = 00001110b, CF=0. RET C O r r OF=0 if first operand keeps original sign. SAHF No operands Store AH register into low 8 bits of Flags register.
Algorithm:
flags register = AH
AH bit: 7 6 5 4 3 2 1 0 [SF] [ZF] [0] [AF] [0] [PF] [1] [CF] bits 1, 3, 5 are reserved.
C Z S O P A r r r r r r SAL memory, immediate
REG, immediate
memory, CL
REG, CL Shift Arithmetic operand1 Left. The number of shifts is set by operand2.
Algorithm:
ADDRESSING MODES
The 8051 instructions use eight addressing modes. These are:
1. Register
2. Direct
3. Indirect
4. Immediate
5. Relative
6. Absolute
7. Long
8. Indexed
1. Register Addressing
In this mode the data, which the instruction operates on, is in one of eight registers labeled R0 to R7 (Rn, in
general). These registers are to be found in one of four register banks, only one of which can be active at any
one time. The active bank may be selected by using bit 3 and bit 4 of the PSW (rs0 & rs1). On power-up or
reset, the default register bank is bank 0. The format of an instruction using register addressing:
For example, to logically OR the contents of accumulator A with that of register R3, the following instruction is
used:
ORL A, R3
and the op-code is 01001011B. The upper five bits, 01001, indicate the instruction, and the lower three bits, 011,
the register.
2. Direct Addressing
Instructions using direct addressing consists of two bytes: op-code and address.
Such instructions can access any on-chip variable or hardware register. Note that the most significant bit of the
direct address determines which area in the on-chip is to be accessed. An address between 00H and 7FH
accesses a location in the low-order on-chip RAM. Any address with bit 7 = 1 refers to one of the special
function registers. It is not necessary to remember the addresses of these special function registers. The
assembler usually understands and converts the mnemonic of a special function register, e.g. P2 for Port 2, into
the appropriate address. An example of a direct addressing instruction is
MOV P1, A
which transfer the content of the accumulator to Port 1. The direct address of Port 1 (90H) is determined by the
assembler and inserted as byte 2 of the instruction. The source of the data, the accumulator, is specified
implicitly in the op-code. The complete encoding of this instruction is
3. Indirect Addressing
In this mode of addressing the instruction performs an operation on the data whose address is contained in
register R0 or R1. Instructions using indirect addressing are single byte instructions. In 8051 assembly language
the symbol @ before R0 or R1 denotes indirect addressing. An example of an indirect addressing instruction is
SUBB A, @R0
This instruction performs the operation: (A) ¬ (A) - (C) - ((R0)).
Op code n
Op code Direct address
10001001 10010000
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4. Immediate Addressing
In an instruction that uses immediate addressing, the operand of the instruction is given as the byte that follows
the op-code. The operand may be a numeric constant, a symbolic variable, or an arithmetic expression using
constants, symbols, and operators. In assembly language we use the symbol # before an operand to denote
immediate addressing. An example of an instruction using immediate addressing is
ANL A, #77
which performs the operation: (A) ¬ (A) · #77.
5. Relative Addressing
Sometimes this is also called program counter relative addressing. This addressing mode is used only with
certain jump instructions. A relative address (or offset) is an 8-bit signed value, which is added to the program
counter to form the address of the next instruction executed. The range for such a jump instruction is -128 to
+127 locations. Although the range is rather limited, relative addressing does offers the advantage of providing
position-independent code (since absolute addresses are not used). For example, the instruction
JZ rel
performs the following operations:
(PC) ¬ (PC) + 2
IF (A) = 0
THEN (PC) ¬ (PC) + rel
ELSE continue
The branch destination is computed by adding the signed relative-displacement in the second instruction byte to
the PC, after incrementing the PC twice.
6. Absolute Addressing
There are only two instructions that use this addressing: ACALL (absolute call) and AJMP (absolute jump).
These instructions perform branching within the current 2K page of program memory. The branch address is
obtained by successively concatenating the five high-order bits of the program counter, bits 5 - 7 of the op-code,
and the second byte of the instruction. The diagram illustrate how this is done:
Note that the branch destination address is within the same 2K page of program memory because the highest
most five address bits are the same as those in the program counter before the branch is taken.
A15A14 A13A12A11 x x x x x x x x x x x
A10 A9 A8 - - - - - A7 A6 A5 A4 A3 A2 A1 A0
A15A14 A13A12A11A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
Incremented PC:
Instruction op code Instruction 2nd byte
Branch address:
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7. Long Addressing
Only two instructions use this addressing mode. These instructions are LCALL addr16 and LJMP addr16.
Both of these are three byte instructions with the op-code being the first byte and the following two bytes are the
address high-byte and address low-byte respectively. These instructions enable the program to branch to
anywhere within the full 64 K-bytes of program memory address space.
8. Indexed Addressing
In this mode the 16-bit address in a base register is added to a positive offset to form an effective address for the
jump indirect instruction JMP @A+DPTR, and the two move code byte instructions MOVC A,@A+DPTR
and MOVC A,@A+PC. The base register in the jump instruction is the data pointer and the positive offset is
held in the accumulator. For the move instructions the base register can either be the data pointer or the program
counter, and again the positive offset is in the accumulator. The operations of these three instructions are as
follows:
JMP @A+DPTR (PC) ¬ (A) +(DPTR)
MOVC A,@A+DPTR (A) ¬ ((A) + (DPTR))
MOVC A,@A+PC (PC) ¬ (PC) + 1
(A) ¬ ((A) + (PC))
In 8086 the instruction queue is 6 byte long. This is because even the longest 8086 instruction is 6 byte long. Thus it is possible to prefetch even the longest instruction in the instruction set.
The CMPS instruction in the 8086/8088 is compare string. It iterates until CX is zero, or [DS:SI] is not equal to [ES:DI], incrementing (or decrementing if DF is set) SI and DI, and decrementing CX along the way.
In the 8086/8088, the overflow flag is set when the result of an arithmetic instruction exceeds the bounds of the signed representation of a number. This is not the same as the carry flag, which is used for the unsigned representation. Both flags get set as needed. You decide which one to pay attention to.
No. They have a different instruction set. However, the processors are sufficiently similar that an 8086 assembler could assemble an 8085 program, given appropriate constants and macros. Some things, however, such as RIM, SIM, RST, etc. do not have equivalents in the 8086.
There is one instruction set in the IA-32. Instruction set is the set of instruction that a processor can execute.
The major difference between the 8085 and the 8086/8088 is that the 8085 is an 8 bit computer, and the 8086/8088 is a 16 bit computer.
Instruction sets are just the opcodes in the CPU that tell it what to do and which software can use. There are hundreds to thousands of these instructions. These instructions vary per processor you use. Here are some of the common instruction sets:x86 - started with the Intel 8086 and mostly still available on PCsx64 - AMD's new instruction set to expand the x86 instruction set to use 64-bit instructions.IA-64 - The instruction set of Intel's Itanium processor, it is declining in popularity as Intel and the software manufacturers have shifted to the x64 instruction set.Z80 - This was an 8-bit instruction set used to run the CP/M operating system. The original TRS-80 used it.68000 - The Motorola 68000 was a 16-32 bit CPU.
Because that's how Intel designed it. They chose a 6 byte queue in the 8086 in order to optimize speed versus latency of the execution unit versus the bus interface unit. The decision for 6 bytes, as compared to 4 or 8 or some other number was a cost tradeoff and a recognition of the average mix of instruction execution cycle times in a typical processing thread.
there are 74 instruction sets in the 8085 up which consist of 246 bit pattern.
RISC - Reduced Instruction Set Computer CISC - Comples Instruction Set Computer
An instruction queue is used in the 8086 to speed up the average time it takes to process an instruction. Some instructions are faster than the bus, while some are slower. If the CPU had to wait for all of the instructions, there would be gaps of time where the CPU is doing nothing. The queue helps to eliminate that gap by prefetching instructions in the hope that they will be ready for use when the CPU gets to them.
Co processor(8087 for 8086,80287 for 80286 etc) is also known as Math processor.It is a dedicated processor for performing arithmetic operations.It has very strong instruction set for numerical operations,faster than 8086 by 4 times.Normally 8086 and other microprocessors will take a lot of time to perform numerical operations and so in multiprocessor mode 8087 will work together with 8086 to solve numerical pronblems. The programmer can write a program with 8086 instructions and 8087 instructions together and so the speed will be improved.