Microprocessor 8086 instructions
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The document describes the instruction set of the 8086 microprocessor. It discusses 6 types of instructions supported: 1) data transfer instructions, 2) arithmetic instructions, 3) logical instructions, 4) string manipulation instructions, 5) process control instructions, and 6) control transfer instructions. Details are provided on the various instructions under each type, including their mnemonics and functions.
![1. Data Transfer Instructions
Instruction Set
5
8086 Microprocessor
Mnemonics: MOV, XCHG, PUSH, POP, IN, OUT …
IN A, [DX]
IN AL, [DX]
IN AX, [DX]
PORTaddr = (DX)
(AL) (PORT)
PORTaddr = (DX)
(AX) (PORT)
IN A, addr8
IN AL, addr8
IN AX, addr8
(AL) (addr8)
(AX) (addr8)
OUT [DX], A
OUT [DX], AL
OUT [DX], AX
PORTaddr = (DX)
(PORT) (AL)
PORTaddr = (DX)
(PORT) (AX)
OUT addr8, A
OUT addr8, AL
OUT addr8, AX
(addr8) (AL)
(addr8) (AX)](https://image.slidesharecdn.com/zrnll7i1qdxstnfzumie-signature-ad224fd12772c8ba4d6ec3d0faf67b8d1a311a34ed511756c0edc8df8f05e6ff-poli-151221104932/85/Microprocessor-8086-instructions-5-320.jpg)
![Assemble Directives
46
8086 Microprocessor
DB
DW
SEGMENT
ENDS
ASSUME
ORG
END
EVEN
EQU
PROC
ENDP
FAR
NEAR
SHORT
MACRO
ENDM
PROC Indicates the beginning of a procedure
ENDP End of procedure
FAR Intersegment call
NEAR Intrasegment call
General form
procname PROC[NEAR/ FAR]
…
…
…
RET
procname ENDP
Program statements of the
procedure
Last statement of the
procedure
User defined name of
the procedure](https://image.slidesharecdn.com/zrnll7i1qdxstnfzumie-signature-ad224fd12772c8ba4d6ec3d0faf67b8d1a311a34ed511756c0edc8df8f05e6ff-poli-151221104932/85/Microprocessor-8086-instructions-46-320.jpg)
![Assemble Directives
49
8086 Microprocessor
DB
DW
SEGMENT
ENDS
ASSUME
ORG
END
EVEN
EQU
PROC
ENDP
FAR
NEAR
SHORT
MACRO
ENDM
MACRO Indicate the beginning of a macro
ENDM End of a macro
General form:
macroname MACRO[Arg1, Arg2 ...]
…
…
…
macroname ENDM
Program
statements in
the macro
User defined name of
the macro](https://image.slidesharecdn.com/zrnll7i1qdxstnfzumie-signature-ad224fd12772c8ba4d6ec3d0faf67b8d1a311a34ed511756c0edc8df8f05e6ff-poli-151221104932/85/Microprocessor-8086-instructions-49-320.jpg)
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Microprocessor 8086 instructions
- 1. 1. Data Transfer Instructions 2. Arithmetic Instructions 3. Logical Instructions 4. String manipulation Instructions 5. Process Control Instructions 6. Control Transfer Instructions Instruction Set 1 8086 Microprocessor 8086 supports 6 types of instructions:
- 2. 1. Data Transfer Instructions Instruction Set 2 8086 Microprocessor Instructions that are used to transfer data/ address in to registers, memory locations and I/O ports. Generally involve two operands: Source operand and Destination operand of the same size. Source: Register or a memory location or an immediate data Destination : Register or a memory location. The size should be a either a byte or a word. A 8-bit data can only be moved to 8-bit register/ memory and a 16-bit data can be moved to 16-bit register/ memory.
- 3. 1. Data Transfer Instructions Instruction Set 3 8086 Microprocessor Mnemonics: MOV, XCHG, PUSH, POP, IN, OUT … MOV reg2/ mem, reg1/ mem MOV reg2, reg1 MOV mem, reg1 MOV reg2, mem (reg2) (reg1) (mem) (reg1) (reg2) (mem) MOV reg/ mem, data MOV reg, data MOV mem, data (reg) data (mem) data XCHG reg2/ mem, reg1 XCHG reg2, reg1 XCHG mem, reg1 (reg2) (reg1) (mem) (reg1)
- 4. 1. Data Transfer Instructions Instruction Set 4 8086 Microprocessor Mnemonics: MOV, XCHG, PUSH, POP, IN, OUT … PUSH reg16/ mem PUSH reg16 PUSH mem (SP) (SP) – 2 MA S = (SS) x 1610 + SP (MA S ; MA S + 1) (reg16) (SP) (SP) – 2 MA S = (SS) x 1610 + SP (MA S ; MA S + 1) (mem) POP reg16/ mem POP reg16 POP mem MA S = (SS) x 1610 + SP (reg16) (MA S ; MA S + 1) (SP) (SP) + 2 MA S = (SS) x 1610 + SP (mem) (MA S ; MA S + 1) (SP) (SP) + 2
- 5. 1. Data Transfer Instructions Instruction Set 5 8086 Microprocessor Mnemonics: MOV, XCHG, PUSH, POP, IN, OUT … IN A, [DX] IN AL, [DX] IN AX, [DX] PORTaddr = (DX) (AL) (PORT) PORTaddr = (DX) (AX) (PORT) IN A, addr8 IN AL, addr8 IN AX, addr8 (AL) (addr8) (AX) (addr8) OUT [DX], A OUT [DX], AL OUT [DX], AX PORTaddr = (DX) (PORT) (AL) PORTaddr = (DX) (PORT) (AX) OUT addr8, A OUT addr8, AL OUT addr8, AX (addr8) (AL) (addr8) (AX)
- 6. 2. Arithmetic Instructions Instruction Set 6 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… ADD reg2/ mem, reg1/mem ADC reg2, reg1 ADC reg2, mem ADC mem, reg1 (reg2) (reg1) + (reg2) (reg2) (reg2) + (mem) (mem) (mem)+(reg1) ADD reg/mem, data ADD reg, data ADD mem, data (reg) (reg)+ data (mem) (mem)+data ADD A, data ADD AL, data8 ADD AX, data16 (AL) (AL) + data8 (AX) (AX) +data16
- 7. 2. Arithmetic Instructions Instruction Set 7 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… ADC reg2/ mem, reg1/mem ADC reg2, reg1 ADC reg2, mem ADC mem, reg1 (reg2) (reg1) + (reg2)+CF (reg2) (reg2) + (mem)+CF (mem) (mem)+(reg1)+CF ADC reg/mem, data ADC reg, data ADC mem, data (reg) (reg)+ data+CF (mem) (mem)+data+CF ADDC A, data ADD AL, data8 ADD AX, data16 (AL) (AL) + data8+CF (AX) (AX) +data16+CF
- 8. 2. Arithmetic Instructions Instruction Set 8 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… SUB reg2/ mem, reg1/mem SUB reg2, reg1 SUB reg2, mem SUB mem, reg1 (reg2) (reg1) - (reg2) (reg2) (reg2) - (mem) (mem) (mem) - (reg1) SUB reg/mem, data SUB reg, data SUB mem, data (reg) (reg) - data (mem) (mem) - data SUB A, data SUB AL, data8 SUB AX, data16 (AL) (AL) - data8 (AX) (AX) - data16
- 9. 2. Arithmetic Instructions Instruction Set 9 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… SBB reg2/ mem, reg1/mem SBB reg2, reg1 SBB reg2, mem SBB mem, reg1 (reg2) (reg1) - (reg2) - CF (reg2) (reg2) - (mem)- CF (mem) (mem) - (reg1) –CF SBB reg/mem, data SBB reg, data SBB mem, data (reg) (reg) – data - CF (mem) (mem) - data - CF SBB A, data SBB AL, data8 SBB AX, data16 (AL) (AL) - data8 - CF (AX) (AX) - data16 - CF
- 10. 2. Arithmetic Instructions Instruction Set 10 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… INC reg/ mem INC reg8 INC reg16 INC mem (reg8) (reg8) + 1 (reg16) (reg16) + 1 (mem) (mem) + 1 DEC reg/ mem DEC reg8 DEC reg16 DEC mem (reg8) (reg8) - 1 (reg16) (reg16) - 1 (mem) (mem) - 1
- 11. 2. Arithmetic Instructions Instruction Set 11 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… MUL reg/ mem MUL reg MUL mem For byte : (AX) (AL) x (reg8) For word : (DX)(AX) (AX) x (reg16) For byte : (AX) (AL) x (mem8) For word : (DX)(AX) (AX) x (mem16) IMUL reg/ mem IMUL reg IMUL mem For byte : (AX) (AL) x (reg8) For word : (DX)(AX) (AX) x (reg16) For byte : (AX) (AX) x (mem8) For word : (DX)(AX) (AX) x (mem16)
- 12. 2. Arithmetic Instructions Instruction Set 12 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… DIV reg/ mem DIV reg DIV mem For 16-bit :- 8-bit : (AL) (AX) :- (reg8) Quotient (AH) (AX) MOD(reg8) Remainder For 32-bit :- 16-bit : (AX) (DX)(AX) :- (reg16) Quotient (DX) (DX)(AX) MOD(reg16) Remainder For 16-bit :- 8-bit : (AL) (AX) :- (mem8) Quotient (AH) (AX) MOD(mem8) Remainder For 32-bit :- 16-bit : (AX) (DX)(AX) :- (mem16) Quotient (DX) (DX)(AX) MOD(mem16) Remainder
- 13. 2. Arithmetic Instructions Instruction Set 13 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… IDIV reg/ mem IDIV reg IDIV mem For 16-bit :- 8-bit : (AL) (AX) :- (reg8) Quotient (AH) (AX) MOD(reg8) Remainder For 32-bit :- 16-bit : (AX) (DX)(AX) :- (reg16) Quotient (DX) (DX)(AX) MOD(reg16) Remainder For 16-bit :- 8-bit : (AL) (AX) :- (mem8) Quotient (AH) (AX) MOD(mem8) Remainder For 32-bit :- 16-bit : (AX) (DX)(AX) :- (mem16) Quotient (DX) (DX)(AX) MOD(mem16) Remainder
- 14. 2. Arithmetic Instructions Instruction Set 14 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… CMP reg2/mem, reg1/ mem CMP reg2, reg1 CMP reg2, mem CMP mem, reg1 Modify flags (reg2) – (reg1) If (reg2) > (reg1) then CF=0, ZF=0, SF=0 If (reg2) < (reg1) then CF=1, ZF=0, SF=1 If (reg2) = (reg1) then CF=0, ZF=1, SF=0 Modify flags (reg2) – (mem) If (reg2) > (mem) then CF=0, ZF=0, SF=0 If (reg2) < (mem) then CF=1, ZF=0, SF=1 If (reg2) = (mem) then CF=0, ZF=1, SF=0 Modify flags (mem) – (reg1) If (mem) > (reg1) then CF=0, ZF=0, SF=0 If (mem) < (reg1) then CF=1, ZF=0, SF=1 If (mem) = (reg1) then CF=0, ZF=1, SF=0
- 15. 2. Arithmetic Instructions Instruction Set 15 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… CMP reg/mem, data CMP reg, data CMP mem, data Modify flags (reg) – (data) If (reg) > data then CF=0, ZF=0, SF=0 If (reg) < data then CF=1, ZF=0, SF=1 If (reg) = data then CF=0, ZF=1, SF=0 Modify flags (mem) – (mem) If (mem) > data then CF=0, ZF=0, SF=0 If (mem) < data then CF=1, ZF=0, SF=1 If (mem) = data then CF=0, ZF=1, SF=0
- 16. 2. Arithmetic Instructions Instruction Set 16 8086 Microprocessor Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP… CMP A, data CMP AL, data8 CMP AX, data16 Modify flags (AL) – data8 If (AL) > data8 then CF=0, ZF=0, SF=0 If (AL) < data8 then CF=1, ZF=0, SF=1 If (AL) = data8 then CF=0, ZF=1, SF=0 Modify flags (AX) – data16 If (AX) > data16 then CF=0, ZF=0, SF=0 If (mem) < data16 then CF=1, ZF=0, SF=1 If (mem) = data16 then CF=0, ZF=1, SF=0
- 17. 3. Logical Instructions Instruction Set 17 8086 Microprocessor Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …
- 18. 3. Logical Instructions Instruction Set 18 8086 Microprocessor Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …
- 19. 3. Logical Instructions Instruction Set 19 8086 Microprocessor Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …
- 20. 3. Logical Instructions Instruction Set 20 8086 Microprocessor Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …
- 21. 3. Logical Instructions Instruction Set 21 8086 Microprocessor Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …
- 22. 3. Logical Instructions Instruction Set 22 8086 Microprocessor Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …
- 23. 3. Logical Instructions Instruction Set 23 8086 Microprocessor Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …
- 24. 3. Logical Instructions Instruction Set 24 8086 Microprocessor Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …
- 25. 4. String Manipulation Instructions Instruction Set 25 8086 Microprocessor String : Sequence of bytes or words 8086 instruction set includes instruction for string movement, comparison, scan, load and store. REP instruction prefix : used to repeat execution of string instructions String instructions end with S or SB or SW. S represents string, SB string byte and SW string word. Offset or effective address of the source operand is stored in SI register and that of the destination operand is stored in DI register. Depending on the status of DF, SI and DI registers are automatically updated. DF = 0 SI and DI are incremented by 1 for byte and 2 for word. DF = 1 SI and DI are decremented by 1 for byte and 2 for word.
- 26. 4. String Manipulation Instructions Instruction Set 26 8086 Microprocessor Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS REP REPZ/ REPE (Repeat CMPS or SCAS until ZF = 0) REPNZ/ REPNE (Repeat CMPS or SCAS until ZF = 1) While CX 0 and ZF = 1, repeat execution of string instruction and (CX) (CX) – 1 While CX 0 and ZF = 0, repeat execution of string instruction and (CX) (CX) - 1
- 27. 4. String Manipulation Instructions Instruction Set 27 8086 Microprocessor Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS MOVS MOVSB MOVSW MA = (DS) x 1610 + (SI) MAE = (ES) x 1610 + (DI) (MAE) (MA) If DF = 0, then (DI) (DI) + 1; (SI) (SI) + 1 If DF = 1, then (DI) (DI) - 1; (SI) (SI) - 1 MA = (DS) x 1610 + (SI) MAE = (ES) x 1610 + (DI) (MAE ; MAE + 1) (MA; MA + 1) If DF = 0, then (DI) (DI) + 2; (SI) (SI) + 2 If DF = 1, then (DI) (DI) - 2; (SI) (SI) - 2
- 28. 4. String Manipulation Instructions Instruction Set 28 8086 Microprocessor Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS CMPS CMPSB CMPSW MA = (DS) x 1610 + (SI) MAE = (ES) x 1610 + (DI) Modify flags (MA) - (MAE) If (MA) > (MAE), then CF = 0; ZF = 0; SF = 0 If (MA) < (MAE), then CF = 1; ZF = 0; SF = 1 If (MA) = (MAE), then CF = 0; ZF = 1; SF = 0 For byte operation If DF = 0, then (DI) (DI) + 1; (SI) (SI) + 1 If DF = 1, then (DI) (DI) - 1; (SI) (SI) - 1 For word operation If DF = 0, then (DI) (DI) + 2; (SI) (SI) + 2 If DF = 1, then (DI) (DI) - 2; (SI) (SI) - 2 Compare two string byte or string word
- 29. 4. String Manipulation Instructions Instruction Set 29 8086 Microprocessor Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS SCAS SCASB SCASW MAE = (ES) x 1610 + (DI) Modify flags (AL) - (MAE) If (AL) > (MAE), then CF = 0; ZF = 0; SF = 0 If (AL) < (MAE), then CF = 1; ZF = 0; SF = 1 If (AL) = (MAE), then CF = 0; ZF = 1; SF = 0 If DF = 0, then (DI) (DI) + 1 If DF = 1, then (DI) (DI) – 1 MAE = (ES) x 1610 + (DI) Modify flags (AL) - (MAE) If (AX) > (MAE ; MAE + 1), then CF = 0; ZF = 0; SF = 0 If (AX) < (MAE ; MAE + 1), then CF = 1; ZF = 0; SF = 1 If (AX) = (MAE ; MAE + 1), then CF = 0; ZF = 1; SF = 0 If DF = 0, then (DI) (DI) + 2 If DF = 1, then (DI) (DI) – 2 Scan (compare) a string byte or word with accumulator
- 30. 4. String Manipulation Instructions Instruction Set 30 8086 Microprocessor Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS LODS LODSB LODSW MA = (DS) x 1610 + (SI) (AL) (MA) If DF = 0, then (SI) (SI) + 1 If DF = 1, then (SI) (SI) – 1 MA = (DS) x 1610 + (SI) (AX) (MA ; MA + 1) If DF = 0, then (SI) (SI) + 2 If DF = 1, then (SI) (SI) – 2 Load string byte in to AL or string word in to AX
- 31. 4. String Manipulation Instructions Instruction Set 31 8086 Microprocessor Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS STOS STOSB STOSW MAE = (ES) x 1610 + (DI) (MAE) (AL) If DF = 0, then (DI) (DI) + 1 If DF = 1, then (DI) (DI) – 1 MAE = (ES) x 1610 + (DI) (MAE ; MAE + 1 ) (AX) If DF = 0, then (DI) (DI) + 2 If DF = 1, then (DI) (DI) – 2 Store byte from AL or word from AX in to string
- 32. Mnemonics Explanation STC Set CF 1 CLC Clear CF 0 CMC Complement carry CF CF/ STD Set direction flag DF 1 CLD Clear direction flag DF 0 STI Set interrupt enable flag IF 1 CLI Clear interrupt enable flag IF 0 NOP No operation HLT Halt after interrupt is set WAIT Wait for TEST pin active ESC opcode mem/ reg Used to pass instruction to a coprocessor which shares the address and data bus with the 8086 LOCK Lock bus during next instruction 5. Processor Control Instructions Instruction Set 32 8086 Microprocessor
- 33. 6. Control Transfer Instructions Instruction Set 33 8086 Microprocessor Transfer the control to a specific destination or target instruction Do not affect flags Mnemonics Explanation CALL reg/ mem/ disp16 Call subroutine RET Return from subroutine JMP reg/ mem/ disp8/ disp16 Unconditional jump 8086 Unconditional transfers
- 34. 6. Control Transfer Instructions Instruction Set 34 8086 Microprocessor 8086 signed conditional branch instructions 8086 unsigned conditional branch instructions Checks flags If conditions are true, the program control is transferred to the new memory location in the same segment by modifying the content of IP
- 35. 6. Control Transfer Instructions Instruction Set 35 8086 Microprocessor Name Alternate name JE disp8 Jump if equal JZ disp8 Jump if result is 0 JNE disp8 Jump if not equal JNZ disp8 Jump if not zero JG disp8 Jump if greater JNLE disp8 Jump if not less or equal JGE disp8 Jump if greater than or equal JNL disp8 Jump if not less JL disp8 Jump if less than JNGE disp8 Jump if not greater than or equal JLE disp8 Jump if less than or equal JNG disp8 Jump if not greater 8086 signed conditional branch instructions 8086 unsigned conditional branch instructions Name Alternate name JE disp8 Jump if equal JZ disp8 Jump if result is 0 JNE disp8 Jump if not equal JNZ disp8 Jump if not zero JA disp8 Jump if above JNBE disp8 Jump if not below or equal JAE disp8 Jump if above or equal JNB disp8 Jump if not below JB disp8 Jump if below JNAE disp8 Jump if not above or equal JBE disp8 Jump if below or equal JNA disp8 Jump if not above
- 36. 6. Control Transfer Instructions Instruction Set 36 8086 Microprocessor Mnemonics Explanation JC disp8 Jump if CF = 1 JNC disp8 Jump if CF = 0 JP disp8 Jump if PF = 1 JNP disp8 Jump if PF = 0 JO disp8 Jump if OF = 1 JNO disp8 Jump if OF = 0 JS disp8 Jump if SF = 1 JNS disp8 Jump if SF = 0 JZ disp8 Jump if result is zero, i.e, Z = 1 JNZ disp8 Jump if result is not zero, i.e, Z = 1 8086 conditional branch instructions affecting individual flags
- 37. 8086 Instruction Set: Summary AND Logical AND of byte or word NOT Logical NOT of byte or word OR Logical OR of byte or word RCL Rotate left trough carry byte or word RCR Rotate right trough carry byte or word ROL Rotate left byte or word ROR Rotate right byte or word SAL Arithmetic shift left byte or word SAR Arithmetic shift right byte or word SHL Logical shift left byte or word SHR Logical shift right byte or word TEST Test byte or word XOR Logical exclusive-OR of byte or word CMPS Compare byte or word string LODS Load byte or word string IN Input byte or word from port OUT Output byte or word to MOV Move to/from register/memory MOVS Move byte or word string MOVSB Move string byte MOVSW Move string word
- 38. 8086 Instruction Set: Summary 38 DAA Decimal adjust for addition DAS Decimal adjust for subtraction DEC Decrement byte or word by one DIV Divide byte or word IDIV Integer divide byte or word IMUL Integer multiply byte or word INC Increment byte or word by one MUL Multiply byte or word (unsigned) NEG Negate byte or word SBB Subtract byte or word and carry (borrow) SUB Subtract byte or word REP Repeat REPE Repeat while equal REPZ Repeat while zero REPNE Repeat while not equal REPNZ Repeat while not zero SCAS Scan byte or word string STOS Store byte or word string
- 39. 8086 Instruction Set: Summary LAHF Load AH from flags LDS Load pointer using data segment LEA Load effective address LES Load pointer using extra segment port POP Pop word off stack POPF Pop flags off stack PUSH Push word onto stack PUSHF Push flags onto stack SAHF Store AH into flags XCHG Exchange byte or word XLAT Translate byte AAA ASCII adjust for addition AAD ASCII adjust for division AAM ASCII adjust for multiply AAS ASCII adjust for subtraction ADC Add byte or word plus carry ADD Add byte or word CBW Convert byte or word CMP Compare byte or word CWD Convert word to double-word
- 40. Assemble Directives 40 8086 Microprocessor Instructions to the Assembler regarding the program being executed. Control the generation of machine codes and organization of the program; but no machine codes are generated for assembler directives. Also called ‘pseudo instructions’ Used to : › specify the start and end of a program › attach value to variables › allocate storage locations to input/ output data › define start and end of segments, procedures, macros etc..
- 41. Assemble Directives 41 8086 Microprocessor Define Byte Define a byte type (8-bit) variable Reserves specific amount of memory locations to each variable Range : 00H – FFH for unsigned value; 00H – 7FH for positive value and 80H – FFH for negative value General form : variable DB value/ values Example: LIST DB 7FH, 42H, 35H Three consecutive memory locations are reserved for the variable LIST and each data specified in the instruction are stored as initial value in the reserved memory location DB DW SEGMENT ENDS ASSUME ORG END EVEN EQU PROC FAR NEAR ENDP SHORT MACRO ENDM
- 42. Assemble Directives 42 8086 Microprocessor Define Word Define a word type (16-bit) variable Reserves two consecutive memory locations to each variable Range : 0000H – FFFFH for unsigned value; 0000H – 7FFFH for positive value and 8000H – FFFFH for negative value General form : variable DW value/ values Example: ALIST DW 6512H, 0F251H, 0CDE2H Six consecutive memory locations are reserved for the variable ALIST and each 16-bit data specified in the instruction is stored in two consecutive memory location. DB DW SEGMENT ENDS ASSUME ORG END EVEN EQU PROC FAR NEAR ENDP SHORT MACRO ENDM
- 43. Assemble Directives 43 8086 Microprocessor SEGMENT : Used to indicate the beginning of a code/ data/ stack segment ENDS : Used to indicate the end of a code/ data/ stack segment General form: Segnam SEGMENT … … … … … … Segnam ENDS Program code or Data Defining Statements User defined name of the segment DB DW SEGMENT ENDS ASSUME ORG END EVEN EQU PROC FAR NEAR ENDP SHORT MACRO ENDM
- 44. Assemble Directives 44 8086 Microprocessor DB DW SEGMENT ENDS ASSUME ORG END EVEN EQU PROC FAR NEAR ENDP SHORT MACRO ENDM Informs the assembler the name of the program/ data segment that should be used for a specific segment. General form: Segment Register ASSUME segreg : segnam, .. , segreg : segnam User defined name of the segment ASSUME CS: ACODE, DS:ADATA Tells the compiler that the instructions of the program are stored in the segment ACODE and data are stored in the segment ADATA Example:
- 45. Assemble Directives 45 8086 Microprocessor DB DW SEGMENT ENDS ASSUME ORG END EVEN EQU PROC FAR NEAR ENDP SHORT MACRO ENDM ORG (Origin) is used to assign the starting address (Effective address) for a program/ data segment END is used to terminate a program; statements after END will be ignored EVEN : Informs the assembler to store program/ data segment starting from an even address EQU (Equate) is used to attach a value to a variable ORG 1000H Informs the assembler that the statements following ORG 1000H should be stored in memory starting with effective address 1000H LOOP EQU 10FEH Value of variable LOOP is 10FEH _SDATA SEGMENT ORG 1200H A DB 4CH EVEN B DW 1052H _SDATA ENDS In this data segment, effective address of memory location assigned to A will be 1200H and that of B will be 1202H and 1203H. Examples:
- 46. Assemble Directives 46 8086 Microprocessor DB DW SEGMENT ENDS ASSUME ORG END EVEN EQU PROC ENDP FAR NEAR SHORT MACRO ENDM PROC Indicates the beginning of a procedure ENDP End of procedure FAR Intersegment call NEAR Intrasegment call General form procname PROC[NEAR/ FAR] … … … RET procname ENDP Program statements of the procedure Last statement of the procedure User defined name of the procedure
- 47. Assemble Directives 47 8086 Microprocessor DB DW SEGMENT ENDS ASSUME ORG END EVEN EQU PROC ENDP FAR NEAR SHORT MACRO ENDM ADD64 PROC NEAR … … … RET ADD64 ENDP The subroutine/ procedure named ADD64 is declared as NEAR and so the assembler will code the CALL and RET instructions involved in this procedure as near call and return CONVERT PROC FAR … … … RET CONVERT ENDP The subroutine/ procedure named CONVERT is declared as FAR and so the assembler will code the CALL and RET instructions involved in this procedure as far call and return Examples:
- 48. Assemble Directives 48 8086 Microprocessor DB DW SEGMENT ENDS ASSUME ORG END EVEN EQU PROC ENDP FAR NEAR SHORT MACRO ENDM Reserves one memory location for 8-bit signed displacement in jump instructions JMP SHORT AHEAD The directive will reserve one memory location for 8-bit displacement named AHEAD Example:
- 49. Assemble Directives 49 8086 Microprocessor DB DW SEGMENT ENDS ASSUME ORG END EVEN EQU PROC ENDP FAR NEAR SHORT MACRO ENDM MACRO Indicate the beginning of a macro ENDM End of a macro General form: macroname MACRO[Arg1, Arg2 ...] … … … macroname ENDM Program statements in the macro User defined name of the macro