U20ECCJ21

MICROPROCESSOR AND MICROCONTROLLER

UNIT I
8086- Architecture, Instruction set, Addressing Modes. Introduction to 8087-
Architecture. Programs for 16 bit Arithmetic, Sorting, Searching and String
operations-Macro assembler Programming for 8086.
MICROPROCESSOR

Microprocessor is a type of miniature electronic device

that contains the arithmetic, logic, and control circuitry
necessary to perform the functions of a digital computer's
central processing unit.

A single integrated circuit chip containing millions of very

small components including transistors, resistors, and
diodes that work together.
8086 IC
 Feature of 8086 Microprocessor
1. Single +5V power supply
2. Clock speed range of 5-10MHz
3. Capable of executing about 0.33 MIPS (Millions
instructions per second)
4. It is 16-bit processor having 16-bit ALU, 16-bit registers,
internal data bus, and 16-bit external data bus resulting
in faster processing.
5. It uses two stages of pipelining, i.e. Fetch Stage and
Execute Stage, which improves performance.
6. Fetch stage can prefetch up to 6 bytes of instructions
and stores them in the queue.
7. It has 256 interrupts.
Block diagram of 8086
 8086 Architecture
EU (Execution Unit) Execution unit gives instructions to BIU
stating from where to fetch the data and then decode and
execute those instructions. Its function is to control operations
on data using the instruction decoder & ALU. EU has no
direct connection with system buses as shown in the above
figure, it performs operations over data through BIU.

BIU (Bus Interface Unit) BIU takes care of all data and
addresses transfers on the buses for the EU like sending
addresses, fetching instructions from the memory, reading
data from the ports and the memory as well as writing data to
the ports and the memory. EU has no direction connection
with System Buses so this is possible with the BIU. EU and
BIU are connected with the Internal Bus.
 8086 Architecture
Functional parts of 8086 microprocessors.

ALU It handles all arithmetic and logical operations, like +, −, ×,

/, OR, AND, NOT operations.

Flag Register It is a 16-bit register that behaves like a flip-flop,

i.e. it changes its status according to the result stored in the
accumulator. It has 9 flags and they are divided into 2 groups −
Conditional Flags and Control Flags.

Instruction queue − BIU contains the instruction queue. BIU

gets upto 6 bytes of next instructions and stores them in the
instruction queue. When EU executes instructions and is ready
for its next instruction, then it simply reads the instruction from
this instruction queue resulting in increased execution speed.
 8086 Architecture
Segment register − BIU has 4 segment buses, i.e. CS, DS, SS&
ES. It holds the addresses of instructions and data in memory,
which are used by the processor to access memory locations. It
also contains 1 pointer register IP, which holds the address of the
next instruction to executed by the EU.
CS − It stands for Code Segment. It is used for addressing a
memory location in the code segment of the memory, where the
executable program is stored.
DS − It stands for Data Segment. It consists of data used by the
program and is accessed in the data segment by an offset address
or the content of other register that holds the offset address.
SS − It stands for Stack Segment. It handles memory to store data
and addresses during execution.
ES − It stands for Extra Segment. ES is additional data segment,
which is used by the string to hold the extra destination data.
Software Model of the 8086 Microprocessors

10
 8086 Registers
General Purpose Index
AH AL
BP
AX

SP
BH BL
BX
SI

CH CL
DI
CX

DH DL
DX Segment

CS

Status and Control SS

Flags DS

IP ES
11
 General Purpose Registers

AX - the Accumulator
BX - the Base Register
CX - the Count Register
DX - the Data Register

Normally used for storing temporary results

Each of the registers is 16 bits wide (AX, BX, CX, DX)
Can be accessed as either 16 or 8 bits AX, AH, AL

12
 General Purpose Registers
•AX
–Accumulator Register
–Preferred register to use in arithmetic, logic and data
transfer instructions because it generates the shortest
Machine Language Code
–Must be used in multiplication and division operations
–Must also be used in I/O operations

•BX
–Base Register
–Also serves as an address register

13
 General Purpose Registers
•CX
–Count register
–Used as a loop counter
–Used in shift and rotate operations

•DX
–Data register
–Used in multiplication and division
–Also used in I/O operations

14
 Pointer and Index Registers

•All 16 bits wide, L/H bytes are not accessible

•Used as memory pointers

Example: MOV AH, [SI]
Move the byte stored in memory location whose address is contained in
register SI to register AH

•IP is not under direct control of the programmer

15
 Flag Register

Overflow Carry
Direction Parity

Interrupt enable Auxiliary Carry

Trap Zero
6 are status flags
Sign
3 are control flag
16
 8086 Programmer’s Model
ES Extra Segment
CS Code Segment
BIU registers
(20 bit adder) SS Stack Segment
DS Data Segment
IP Instruction Pointer

EU registers AX AH AL Accumulator
BX BH BL Base Register
CX CH CL Count Register
DX DH DL Data Register
SP Stack Pointer
BP Base Pointer
SI Source Index Register
DI Destination Index Register
FLAGS

17
 The Stack

•The stack is used for temporary storage of information

such as data or addresses.

•When a CALL is executed, the 8086 automatically

PUSHes the current value of CS and IP onto the stack.

Other registers can also be pushed

Before return from the subroutine, POP instructions can

be used to pop values back from the stack into the
corresponding registers.

18
The Stack

19
 Physical Address Generation in 8086
 The 20-bit physical address is generated by adding 16-bit contents of a
segment register with an 16-bit offset value (also called Effective Address)
which is stored in a corresponding default register (either in IP, BX, SI, DI,
BP or SP. Different segments have different default register for offset, for
example IP is default offset register for Code Segment)
 BIU always appends 4 zeros automatically to the 16-bit address of a segment
register (to make it 20-bit) because it knows the starting address of a
segment always ends with 4 zeros

Points to a memory Offset Value (16 bits)

location within a
segment

CS DS ES SS Segment Register (16 bits) 0 0 00

IP BX DI BP Upper 16bit of starting

address of a segment 20-bits 16-bits
DI SP
Actual address for
SI memory Adder

Default Registers Assigned to store

offset values for different segments Physical Address (20 Bits)
Memory Address Generation

Offset Value (16 bits)

Segment Register (16 bits) 00 00

Adder

Physical Address (20 Bits)

21
 Physical Address Calculation

Offset is derived from the combination of

pointer registers, index registers the
Instruction Pointer, and immediate values Segment address 0000
(called displacement)
+ Offset

Memory address

Examples

CS 3 4 8 A 0 SS 5 0 0 0 0
IP + 4 2 1 4 SP + F F E 0
Instruction 3 8 A B 4 Stac 5 F F E 0
(code) k
addressDS 1 2 3 4 0 addr
ess
DI + 0 0 2 2
Data 1 2 3 6 2
addr
ess
Example of Physical Address
Generation for Code Segment Memory
Start of Code Segment
1 00000H
(348A0H) Data
Segment
IP = 4214H 3

4
Code Byte at 38AB4H
Code
Segment
Extra
Segment
7 1MB
8 Address
9
Range
CS 348A0H 10
11
IP + 4214 H 12
Physical Address 38AB4 H 13
14
15

Stack
Segment FFFFFH
Example of Physical Address Generation
for Data Segment
0H

05C00H
DS: 05C0
05C50H
SI 0050 DS:EA

Memory
05C0 0
Segment Register

Offset + 0050

Physical Address 05C50H 0FFFFFH

Data is fetched with respect to the DS register which contains starting

or base address

The effective address (EA) or offset is in SI (default register for DS)

The EA depends on the addressing mode

Example of Physical Address Generation
for Stack Segment
0H

0A00 0A000H
SS:
0A100H
SP 0100 SS:SP

Memory
0A00 0
Segment Register

Offset + 0100

Physical Address 0A100H 0FFFFFH

The offset is given by the SP register.

The stack is always referenced with respect to the stack segment register.
The stack grows toward decreasing memory locations.
The SP points to the last or top item on the stack.
 8086
ADDRESSING MODES
&
Instruction set
8086 Microprocessor
Introduction

Program
A set of instructions written to solve
a problem.

Instruction
Directions which a microprocessor
follows to execute a task or part of a
task.

Computer language

High Level Low Level

Machine Language Assembly Language

 Binary bits  English Alphabets

 ‘Mnemonics’
 Assembler
Mnemonics  Machine
Language 27
8086 - ADDRESSING MODES
8086 Microprocessor
Addressing Modes

Every instruction of a program has to operate on a data.

The different ways in which a source operand is denoted
in an instruction are known as addressing modes.

1. Register Addressing
Group I : Addressing modes for
2. Immediate Addressing register and immediate data

3. Direct Addressing

4. Register Indirect Addressing

5. Based Addressing
Group II : Addressing modes for
6. Indexed Addressing memory data
7. Based Index Addressing

8. String Addressing

9. Direct I/O port Addressing

Group III : Addressing modes for
10. Indirect I/O port Addressing I/O ports

11. Relative Addressing Group IV : Relative Addressing mode

12. Implied Addressing Group V : Implied Addressing mode

29
8086 Microprocessor Group I : Addressing modes for
Addressing Modes register and immediate data

1. Register Addressing The instruction will specify the name of the

register which holds the data to be operated by
2. Immediate Addressing the instruction.
3. Direct Addressing Example:
4. Register Indirect Addressing
MOV CL, DH
5. Based Addressing
The content of 8-bit register DH is moved to
6. Indexed Addressing another 8-bit register CL

7. Based Index Addressing (CL)  (DH)

8. String Addressing

9. Direct I/O port Addressing

10. Indirect I/O port Addressing

11. Relative Addressing

12. Implied Addressing

30
8086 Microprocessor Group I : Addressing modes for
Addressing Modes register and immediate data

1. Register Addressing
In immediate addressing mode, an 8-bit or 16-bit
2. Immediate Addressing data is specified as part of the instruction
3. Direct Addressing
Example:
4. Register Indirect Addressing
MOV DL, 08H
5. Based Addressing
The 8-bit data (08H) given in the instruction is
6. Indexed Addressing moved to DL

7. Based Index Addressing (DL)  08H

8. String Addressing
MOV AX, 0A9FH
9. Direct I/O port Addressing
The 16-bit data (0A9FH) given in the instruction is
10. Indirect I/O port Addressing
moved to AX register
11. Relative Addressing
(AX)  0A9FH
12. Implied Addressing

31
8086 Microprocessor Group II : Addressing modes
Addressing Modes for memory data

1. Register Addressing

2. Immediate Addressing
Here, the effective address of the memory
3. Direct Addressing
location at which the data operand is stored is
4. Register Indirect Addressing given in the instruction.

5. Based Addressing The effective address is just a 16-bit number

written directly in the instruction.
6. Indexed Addressing
Example:
7. Based Index Addressing
MOV BX, [1354H]
8. String Addressing MOV BL, [0400H]
9. Direct I/O port Addressing
The square brackets around the 1354H denotes
the contents of the memory location. When
10. Indirect I/O port Addressing
executed, this instruction will copy the contents of
11. Relative Addressing the memory location into BX register.

12. Implied Addressing This addressing mode is called direct because the
displacement of the operand from the segment
base is specified directly in the instruction.

32
8086 Microprocessor Group II : Addressing modes
Addressing Modes for memory data

1. Register Addressing In Register indirect addressing, name of the

register which holds the effective address (EA)
2. Immediate Addressing will be specified in the instruction.

3. Direct Addressing Registers used to hold EA are any of the following

registers:
4. Register Indirect Addressing
BX, BP, DI and SI.
5. Based Addressing
Content of the DS register is used for base
6. Indexed Addressing
address calculation.
7. Based Index Addressing
Example:
Note : Register/ memory
8. String Addressing enclosed in brackets refer
MOV CX, [BX]
to content of register/
9. Direct I/O port Addressing memory
Operations:
10. Indirect I/O port Addressing
EA = (BX)
11. Relative Addressing BA = (DS) x 1610
MA = BA + EA
12. Implied Addressing
(CX)  (MA) or,

(CL)  (MA)
(CH)  (MA +1)
33
8086 Microprocessor Group II : Addressing modes
Addressing Modes for memory data

1. Register Addressing In Based Addressing, BX or BP is used to hold the

base value for effective address and a signed 8-bit
2. Immediate Addressing or unsigned 16-bit displacement will be specified
in the instruction.
3. Direct Addressing
In case of 8-bit displacement, it is sign extended
4. Register Indirect Addressing to 16-bit before adding to the base value.

5. Based Addressing When BX holds the base value of EA, 20-bit

physical address is calculated from BX and DS.
6. Indexed Addressing
When BP holds the base value of EA, BP and SS is
7. Based Index Addressing
used.
8. String Addressing
Example:
9. Direct I/O port Addressing
MOV AX, [BX + 08H]
10. Indirect I/O port Addressing
Operations:
11. Relative Addressing
0008H  08H (Sign extended)
12. Implied Addressing EA = (BX) + 0008H
BA = (DS) x 1610
MA = BA + EA

(AX)  (MA) or,

(AL)  (MA)
34
(AH)  (MA + 1)
8086 Microprocessor Group II : Addressing modes
Addressing Modes for memory data

1. Register Addressing SI or DI register is used to hold an index value for

memory data and a signed 8-bit or unsigned 16-
2. Immediate Addressing bit displacement will be specified in the
instruction.
3. Direct Addressing
Displacement is added to the index value in SI or
4. Register Indirect Addressing DI register to obtain the EA.

5. Based Addressing In case of 8-bit displacement, it is sign extended

to 16-bit before adding to the base value.
6. Indexed Addressing

7. Based Index Addressing

Example:
8. String Addressing
MOV CX, [SI + 0A2H]
9. Direct I/O port Addressing
Operations:
10. Indirect I/O port Addressing
FFA2H  A2H (Sign extended)
11. Relative Addressing
EA = (SI) + FFA2H
12. Implied Addressing BA = (DS) x 1610
MA = BA + EA

(CX)  (MA) or,

(CL)  (MA)
(CH)  (MA + 1)
35
8086 Microprocessor Group II : Addressing modes
Addressing Modes for memory data

1. Register Addressing In Based Index Addressing, the effective address

is computed from the sum of a base register (BX
2. Immediate Addressing or BP), an index register (SI or DI) and a
displacement.
3. Direct Addressing
Example:
4. Register Indirect Addressing
MOV DX, [BX + SI + 0AH]
5. Based Addressing
Operations:
6. Indexed Addressing
000AH  0AH (Sign extended)
7. Based Index Addressing

8. String Addressing EA = (BX) + (SI) + 000AH

BA = (DS) x 1610
9. Direct I/O port Addressing MA = BA + EA

10. Indirect I/O port Addressing (DX)  (MA) or,

11. Relative Addressing (DL)  (MA)

(DH)  (MA + 1)
12. Implied Addressing

36
8086 Microprocessor Group II : Addressing modes
Addressing Modes for memory data

1. Register Addressing Employed in string operations to operate on string

data.
2. Immediate Addressing
The effective address (EA) of source data is stored
3. Direct Addressing in SI register and the EA of destination is stored in
DI register.
4. Register Indirect Addressing
Segment register for calculating base address of
5. Based Addressing source data is DS and that of the destination data
is ES
6. Indexed Addressing

7. Based Index Addressing

Example: MOVS BYTE
8. String Addressing
Operations:
9. Direct I/O port Addressing
Calculation of source memory location:
10. Indirect I/O port Addressing EA = (SI) BA = (DS) x 1610 MA = BA + EA

11. Relative Addressing Calculation of destination memory location:

EAE = (DI) BAE = (ES) x 1610 MAE = BAE + EAE
12. Implied Addressing

Note : Effective address of (MAE)  (MA)

the Extra segment register
If DF = 1, then (SI)  (SI) – 1 and (DI) = (DI) - 1
If DF = 0, then (SI)  (SI) +1 and (DI) = (DI)37+ 1
8086 Microprocessor Group III : Addressing
Addressing Modes modes for I/O ports

1. Register Addressing These addressing modes are used to access data

from standard I/O mapped devices or ports.
2. Immediate Addressing
In direct port addressing mode, an 8-bit port
3. Direct Addressing address is directly specified in the instruction.

4. Register Indirect Addressing Example: IN AL, [09H]

5. Based Addressing Operations: PORTaddr = 09H

(AL)  (PORT)
6. Indexed Addressing
Content of port with address 09H is
7. Based Index Addressing
moved to AL register
8. String Addressing
In indirect port addressing mode, the instruction
9. Direct I/O port Addressing will specify the name of the register which holds
the port address. In 8086, the 16-bit port address
10. Indirect I/O port Addressing is stored in the DX register.

11. Relative Addressing Example: OUT [DX], AX

12. Implied Addressing Operations: PORTaddr = (DX)

(PORT)  (AX)

Content of AX is moved to port

whose address is specified by DX
register. 38
8086 Microprocessor Group IV : Relative
Addressing Modes Addressing mode

1. Register Addressing

2. Immediate Addressing

3. Direct Addressing In this addressing mode, the effective address of

a program instruction is specified relative to
4. Register Indirect Addressing Instruction Pointer (IP) by an 8-bit signed
displacement.
5. Based Addressing
Example: JZ 0AH
6. Indexed Addressing
Operations:
7. Based Index Addressing

8. String Addressing 000AH  0AH (sign extend)

9. Direct I/O port Addressing If ZF = 1, then

10. Indirect I/O port Addressing EA = (IP) + 000AH

BA = (CS) x 1610
11. Relative Addressing MA = BA + EA

12. Implied Addressing If ZF = 1, then the program control jumps to

new address calculated above.

If ZF = 0, then next instruction of the

program is executed.
39
8086 Microprocessor Group IV : Implied
Addressing Modes Addressing mode

1. Register Addressing

2. Immediate Addressing

3. Direct Addressing

4. Register Indirect Addressing

5. Based Addressing

6. Indexed Addressing
Instructions using this mode have no operands.
The instruction itself will specify the data to be
7. Based Index Addressing
operated by the instruction.
8. String Addressing
Example: CLC
9. Direct I/O port Addressing
This clears the carry flag to zero.
10. Indirect I/O port Addressing

11. Relative Addressing

12. Implied Addressing

40
8086 - INSTRUCTION SET
8086 Microprocessor
Instruction Set

8086 supports 6 types of instructions.

1. Data Transfer Instructions

2. Arithmetic Instructions

3. Logical Instructions

4. String manipulation Instructions

5. Process Control Instructions

6. Control Transfer Instructions

42
8086 Microprocessor
Instruction Set

1. Data Transfer Instructions

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.

43
8086 Microprocessor
Instruction Set

1. Data Transfer Instructions

Mnemonics: MOV, XCHG, PUSH, POP, IN, OUT …

MOV reg2/ mem, reg1/ mem

MOV reg2, reg1 (reg2)  (reg1)

MOV mem, reg1 (mem)  (reg1)
MOV reg2, mem (reg2)  (mem)

MOV reg/ mem, data

MOV reg, data (reg)  data

MOV mem, data (mem)  data

XCHG reg2/ mem, reg1

XCHG reg2, reg1 (reg2)  (reg1)

XCHG mem, reg1 (mem)  (reg1)

44
8086 Microprocessor
Instruction Set

1. Data Transfer Instructions

Mnemonics: MOV, XCHG, PUSH, POP, IN, OUT …

PUSH reg16/ mem

PUSH reg16 (SP)  (SP) – 2

MA S = (SS) x 1610 + SP
(MA S ; MA S + 1)  (reg16)

PUSH mem (SP)  (SP) – 2

MA S = (SS) x 1610 + SP
(MA S ; MA S + 1)  (mem)

POP reg16/ mem

POP reg16 MA S = (SS) x 1610 + SP

(reg16)  (MA S ; MA S + 1)
(SP)  (SP) + 2

POP mem MA S = (SS) x 1610 + SP

(mem)  (MA S ; MA S + 1)
(SP)  (SP) + 2
45
8086 Microprocessor
Instruction Set

1. Data Transfer Instructions

Mnemonics: MOV, XCHG, PUSH, POP, IN, OUT …

IN A, [DX] OUT [DX], A

IN AL, [DX] PORTaddr = (DX) OUT [DX], AL PORTaddr = (DX)

(AL)  (PORT) (PORT)  (AL)

IN AX, [DX] PORTaddr = (DX) OUT [DX], AX PORTaddr = (DX)

(AX)  (PORT) (PORT)  (AX)

IN A, addr8 OUT addr8, A

IN AL, addr8 (AL)  (addr8) OUT addr8, AL (addr8)  (AL)

IN AX, addr8 (AX)  (addr8) OUT addr8, AX (addr8)  (AX)

46
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

ADD reg2/ mem, reg1/mem

ADC reg2, reg1 (reg2)  (reg1) + (reg2)

ADC reg2, mem (reg2)  (reg2) + (mem)
ADC mem, reg1 (mem)  (mem)+(reg1)

ADD reg/mem, data

ADD reg, data (reg)  (reg)+ data

ADD mem, data (mem)  (mem)+data

ADD A, data

ADD AL, data8 (AL)  (AL) + data8

ADD AX, data16 (AX)  (AX) +data16

47
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

ADC reg2/ mem, reg1/mem

ADC reg2, reg1 (reg2)  (reg1) + (reg2)+CF

ADC reg2, mem (reg2)  (reg2) + (mem)+CF
ADC mem, reg1 (mem)  (mem)+(reg1)+CF

ADC reg/mem, data

ADC reg, data (reg)  (reg)+ data+CF

ADC mem, data (mem)  (mem)+data+CF

ADDC A, data

ADD AL, data8 (AL)  (AL) + data8+CF

ADD AX, data16 (AX)  (AX) +data16+CF

48
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

SUB reg2/ mem, reg1/mem

SUB reg2, reg1 (reg2)  (reg1) - (reg2)

SUB reg2, mem (reg2)  (reg2) - (mem)
SUB mem, reg1 (mem)  (mem) - (reg1)

SUB reg/mem, data

SUB reg, data (reg)  (reg) - data

SUB mem, data (mem)  (mem) - data

SUB A, data

SUB AL, data8 (AL)  (AL) - data8

SUB AX, data16 (AX)  (AX) - data16

49
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

SBB reg2/ mem, reg1/mem

SBB reg2, reg1 (reg2)  (reg1) - (reg2) - CF

SBB reg2, mem (reg2)  (reg2) - (mem)- CF
SBB mem, reg1 (mem)  (mem) - (reg1) –CF

SBB reg/mem, data

SBB reg, data (reg)  (reg) – data - CF

SBB mem, data (mem)  (mem) - data - CF

SBB A, data

SBB AL, data8 (AL)  (AL) - data8 - CF

SBB AX, data16 (AX)  (AX) - data16 - CF

50
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

INC reg/ mem

INC reg8 (reg8)  (reg8) + 1

INC reg16 (reg16)  (reg16) + 1

INC mem (mem)  (mem) + 1

DEC reg/ mem

DEC reg8 (reg8)  (reg8) - 1

DEC reg16 (reg16)  (reg16) - 1

DEC mem (mem)  (mem) - 1

51
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

MUL reg/ mem

MUL reg For byte : (AX)  (AL) x (reg8)

For word : (DX)(AX)  (AX) x (reg16)

MUL mem For byte : (AX)  (AL) x (mem8)

For word : (DX)(AX)  (AX) x (mem16)

IMUL reg/ mem

IMUL reg For byte : (AX)  (AL) x (reg8)

For word : (DX)(AX)  (AX) x (reg16)

IMUL mem For byte : (AX)  (AX) x (mem8)

For word : (DX)(AX)  (AX) x (mem16)

52
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

DIV reg/ mem

DIV reg 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

DIV mem 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

53
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

IDIV reg/ mem

IDIV reg 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

IDIV mem 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

54
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

CMP reg2/mem, reg1/ mem

CMP reg2, 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

CMP reg2, mem 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

CMP mem, reg1 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

55
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

CMP reg/mem, data

CMP reg, 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

CMP mem, data 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

56
8086 Microprocessor
Instruction Set

2. Arithmetic Instructions
Mnemonics: ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP…

CMP A, data

CMP AL, data8 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

CMP AX, data16 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

57
8086 Microprocessor
Instruction Set

3. Logical Instructions
Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …

58
8086 Microprocessor
Instruction Set

3. Logical Instructions
Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …

59
8086 Microprocessor
Instruction Set

3. Logical Instructions
Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …

60
8086 Microprocessor
Instruction Set

3. Logical Instructions
Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …

61
8086 Microprocessor
Instruction Set

3. Logical Instructions
Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …

62
8086 Microprocessor
Instruction Set

3. Logical Instructions
Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …

63
8086 Microprocessor
Instruction Set

3. Logical Instructions
Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …

64
8086 Microprocessor
Instruction Set

3. Logical Instructions
Mnemonics: AND, OR, XOR, TEST, SHR, SHL, RCR, RCL …

65
8086 Microprocessor
Instruction Set

4. String Manipulation Instructions

 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.

66
8086 Microprocessor
Instruction Set

4. String Manipulation Instructions

Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS

REP

REPZ/ REPE While CX  0 and ZF = 1, repeat execution of

string instruction and
(Repeat CMPS or SCAS until (CX)  (CX) – 1
ZF = 0)

REPNZ/ REPNE While CX  0 and ZF = 0, repeat execution of

string instruction and
(Repeat CMPS or SCAS until (CX)  (CX) - 1
ZF = 1)

67
8086 Microprocessor
Instruction Set

4. String Manipulation Instructions

Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS

MOVS

MOVSB 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

MOVSW 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

68
8086 Microprocessor
Instruction Set

4. String Manipulation Instructions

Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS

Compare two string byte or string word

CMPS

CMPSB 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
CMPSW 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

69
8086 Microprocessor
Instruction Set

4. String Manipulation Instructions

Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS
Scan (compare) a string byte or word with accumulator
SCAS

SCASB 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

SCASW 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

70
If DF = 1, then (DI)  (DI) – 2
8086 Microprocessor
Instruction Set

4. String Manipulation Instructions

Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS

Load string byte in to AL or string word in to AX

LODS

LODSB MA = (DS) x 1610 + (SI)

(AL)  (MA)

If DF = 0, then (SI)  (SI) + 1

If DF = 1, then (SI)  (SI) – 1

LODSW MA = (DS) x 1610 + (SI)

(AX)  (MA ; MA + 1)

If DF = 0, then (SI)  (SI) + 2

If DF = 1, then (SI)  (SI) – 2

71
8086 Microprocessor
Instruction Set

4. String Manipulation Instructions

Mnemonics: REP, MOVS, CMPS, SCAS, LODS, STOS

Store byte from AL or word from AX in to string

STOS

STOSB MAE = (ES) x 1610 + (DI)

(MAE)  (AL)

If DF = 0, then (DI)  (DI) + 1

If DF = 1, then (DI)  (DI) – 1

STOSW MAE = (ES) x 1610 + (DI)

(MAE ; MAE + 1 )  (AX)

If DF = 0, then (DI)  (DI) + 2

If DF = 1, then (DI)  (DI) – 2

72
8086 Microprocessor
Instruction Set

5. Processor Control Instructions

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 73

8086 Microprocessor
Instruction Set

6. Control Transfer Instructions

Transfer the control to a specific destination or target instruction

Do not affect flags

 8086 Unconditional transfers

Mnemonics Explanation
CALL reg/ mem/ disp16 Call subroutine

RET Return from subroutine

JMP reg/ mem/ disp8/ disp16 Unconditional jump

74
8086 Microprocessor
Instruction Set

6. Control Transfer Instructions

 8086 signed conditional  8086 unsigned conditional

branch instructions 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

75
8086 Microprocessor
Instruction Set

6. Control Transfer Instructions

 8086 signed conditional  8086 unsigned conditional

branch instructions branch instructions

Name Alternate name Name Alternate name

JE disp8 JZ disp8 JE disp8 JZ disp8
Jump if equal Jump if result is 0 Jump if equal Jump if result is 0

JNE disp8 JNZ disp8 JNE disp8 JNZ disp8

Jump if not equal Jump if not zero Jump if not equal Jump if not zero
JG disp8 JNLE disp8 JA disp8 JNBE disp8
Jump if greater Jump if not less or Jump if above Jump if not below
equal or equal
JGE disp8 JNL disp8 JAE disp8 JNB disp8
Jump if greater Jump if not less Jump if above or Jump if not below
than or equal equal
JL disp8 JNGE disp8 JB disp8 JNAE disp8
Jump if less than Jump if not Jump if below Jump if not above
greater than or or equal
equal
JLE disp8 JNG disp8 JBE disp8 JNA disp8
Jump if less than Jump if not Jump if below or Jump if not above
or equal greater equal 76
8086 Microprocessor
Instruction Set

6. Control Transfer Instructions

 8086 conditional branch instructions affecting individual flags

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

77
 8087 ARCHITECTURE

8087 Architecture is divided into two groups,

Control Unit (CU) and Numeric Extension Unit (NEU).

 The control unit handles all the communication between the processor and the memory such as
it receives and decodes instructions, reads and writes memory operands, maintains parallel
queue, etc. All the coprocessor instructions are ESC instructions, i.e., they start with ‘F’, the
coprocessor only executes the ESC instructions while other instructions are executed by the
microprocessor.

 The numeric Extension Unit handles all the numeric processor instructions like arithmetic,
logical, transcendental, and data transfer instructions. It has 8 register stack, which holds the
operands for instructions and their results.
 8086 PROGRAMS
Addition of two 16 bit data

Subtraction of two 16 bit data

Multiplication of two 16 bit data

Division of two 32 bit data by 16 bit data

Finding the sum of N numbers in an Array

Finding Largest in an Array

Sorting an Array of N Numbers in Ascending order in an Array

Finding Factorial of 8 bit Data

Conversion of BCD to Binary Data

Generation of Fibonacci Series