8086 module 1 & 2 work

INTEL 8086
MICROPROCESSOR
Suresh.P
HOD / ECE
Royal College of Engineering and Technology
Chiramanangad PO, Akkikkavu

MODULE
1 & 2
Complete idea about INTEL 8086
Microprocessor

Topics to be covered
1. Software Architecture of the INTEL 8086.
2. Hardware Architecture of INTEL 8086.
3. 8086 Programming and program development.
RCET Microprocessor & Microcontroller 3

Software architecture of the INTEL
8086
 Memory segmentation and addressing
 Block diagram of 8086
 Address space & Data organization
 Data Types
 Registers
 Stack
 I/O space

Hardware Architecture of INTEL 8086
 Pin Diagram and Pin Details
 min/max mode
 Coprocessor and Multiprocessor configuration
 Hardware organization of address space
 Control signals
 I/O interfaces

8086 programming and program
development.
 Assembly Language Programming.
 Instruction Set.
 Assembler Directives.
 Programming Exercises.

Software Architecture
of
INTEL 8086

Software architecture of the INTEL
8086
 Memory segmentation and addressing
 Block diagram of 8086
 Address space & Data organization
 Data Types
 Registers
 Stack
 I/O space

Memory segmentation and addressing
• Von – Newman architecture & Harvard architecture
• Program Memory & Data Memory
• Need for Segmentation
– To implement Harvard architecture
– Easy to debug
– Same Interfacing ICs can be used
– To avoid overlap of stack with normal memory
– Compatible with 8085

Segmented Memory

Memory Address Generation
• The BIU has a dedicated adder for determining
physical memory addresses.
Offset Value (16 bits)
Segment Register (16 bits) 0 0 0 0
Adder
Physical Address (20 Bits)

Segment : Offset Address
• Logical Address is specified as segment:offset
• Physical address is obtained by shifting the segment
address 4 bits to the left and adding the offset address.
• Thus the physical address of the logical address
A4FB:4872 is:
A4FB0
+ 4872
A9822

Segments, Segment Registers & Offset
Registers
• Segment Size = 64KB
• Maximum number of segments possible = 14
• Logical Address – 16 bits
• Physical Address – 20 bits
• 2 Logical Addresses for each Segments.
– Base Address (16 bits)
– Offset Address (16 bits)
• Segment registers are used to store the Base address of
the segment.

Segments, Segment Registers & Offset
Registers
• 4 Segments in 8086
– Code Segment (CS)
– Data Segment (DS)
– Stack Segment (SS)
– Extra Segment (ES)
SEGMENT SEGMENT
REGISTER
OFFSET REGISTER
Code Segment CSR Instruction Pointer
(IP)
Data Segment DSR Source Index (SI)
Extra Segment ESR Destination Index
(DI)
Stack Segment SSR Stack Pointer (SP) /
Base Pointer (BP)

Block diagram of 8086

Pipelined architecture of the 8086
microprocessors

Execution and bus interface units

Software Model of the 8086 Microprocessors

Address space & Data organization
Memory address space
Storing a word in memory
What is the word in (b) in Hex?

Aligned and misaligned data word

Aligned and misaligned double words of data

Storing double word in memory

Data Types
Unsigned word integer
0 – 65,535
Unsigned byte
integer
0 - 255

Data Types
Signed
integers
-128 - +127
-32,768 - +32,767

Data Types
Binary Coded
Decimal (BCD)
Unpacked BCD
Packed BCD

American Standard Code for Information Interchange
(ASCII)

Dedicated, Reserved, and General use
Memory

8086 Registers
Index
BP
SP
SI
DI
Segment
CS
SS
DS
ES
General Purpose
AH
BH
CH
AL
BL
CL
DH DL
Status and Control
Flags
IP
AX
BX
CX
DX

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

• 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

• 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

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

Flag Register
Carry
Parity
Auxiliary Carry
Zero
Overflow
Direction
Interrupt enable
Trap
Sign
6 are status flags
3 are control flag

8086 Programmer’s Model
ES
CS
SS
DS
IP
AH
BH
CH
DH
AL
BL
CL
DL
SP
BP
SI
DI
FLAGS
AX
BX
CX
DX
Extra Segment
Code Segment
Stack Segment
Data Segment
Instruction Pointer
Accumulator
Base Register
Count Register
Data Register
Stack Pointer
Base Pointer
Source Index Register
Destination Index Register
BIU registers
(20 bit adder)
EU registers

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.

The Stack

Example for PUSH

Example for POP

The I/O address space

Hardware Architecture
of
INTEL 8086

Hardware Architecture of INTEL 8086
 Pin Diagram and Pin Details
 min/max mode
 Coprocessor and Multiprocessor configuration
 Hardware organization of address space
 Control signals
 I/O interfaces

INTEL 8086 - Pin Diagram

INTEL 8086 - Pin Details
Ground
Clock
Duty cycle: 33%
Power Supply
5V  10%
Reset
Registers, seg
regs, flags
CS: FFFFH, IP:
0000H
If high for
minimum 4
clks

Address/Data Bus:
Contains address
bits A15-A0 when ALE
is 1 & data bits D15 –
D0 when ALE is 0.
Address Latch Enable:
When high,
multiplexed
address/data bus
contains address
information.

INTERRUPT
Non - maskable
interrupt
Interrupt request
Interrupt
acknowledge

Direct
Memory
Access
Hold
Hold
acknowledge

Address/Status Bus
Address bits A19 –
A16 & Status bits S6
– S3

Bus High Enable/S7
Enables most
significant data bits
D15 – D8 during read
or write operation.
S7: Always 1.
BHE#, A0:
0,0: Whole word
(16-bits)
0,1: High byte
to/from odd address
1,0: Low byte
to/from even address
1,1: No selection

Min/Max mode
Minimum Mode: +5V
Maximum Mode: 0V
Minimum Mode Pins
Maximum Mode
Pins

Minimum Mode- Pin Details
Data
Transmit/Receive
RCET Microprocessor & Microcontroller
50
Read Signal
Write Signal
Memory or I/0
Data Bus Enable

Maximum Mode - Pin Details
Status Signal
Inputs to 8288 to
generate eliminated
signals due to max
mode.
S2 S1 S0
000: INTA
001: read I/O port
010: write I/O port
011: halt
100: code access
101: read memory
110: write memory
111: none -passive

DMA
Request/Grant
Lock Output
Lock Output
Used to lock peripherals
off the system
Activated by using the
LOCK: prefix on any
instruction

Queue Status
Used by numeric
coprocessor (8087)
QS1 QS0
00: Queue is idle
01: First byte of opcode
10: Queue is empty
11: Subsequent byte of
opcode

Minimum Mode 8086 System

‘Read’ Cycle timing Diagram for
Minimum Mode

‘Write’ Cycle timing Diagram for
Minimum Mode

Maximum Mode 8086 System

• Here, either a numeric coprocessor of the type 8087 or another
processor is interfaced with 8086.
• The Memory, Address Bus, Data Buses are shared resources
between the two processors.
• The control signals for Maximum mode of operation are
generated by the Bus Controller chip 8788.
• The three status outputs S0*, S1*, S2* from the processor are
input to 8788.
• The outputs of the bus controller are the Control Signals, namely
DEN, DT/R*, IORC*, IOWTC*, MWTC*, MRDC*, ALE etc.

Memory Read timing in
Maximum Mode

Memory Write timing in
Maximum Mode

Memory Banking

Interface 8086 to 6116 Static RAM
64
A
____
BHE
ALE
8086
A(10-0)
D(7-0)
__
R/W
OE*
CS*
A(10-0)
__
R/W
OE*
CS*
D
D(7-0)
20
Latch
Addr
Decoder
A(11-1)
21
A0, BHE*
A(19-12)
A(11-1)
__
M/___
IO
WR
___
RD
Low byte
(Even Bank)
D(7-0)
D(15-8)
16
A0
RAMCS*
MEM*
BHE*
6116 (2K x8)
High byte
(Odd Bank)

8086 Interrupts

8086 Interrupts Procedure

8086 External Interrupts

8086 Interrupt Vector Table

Programming
with
INTEL 8086

8086 programming and program
development.
 Assembly Language Programming.
 Instruction Set.
 Assembler Directives.
 Programming Exercises.

General Syntax

x86 Instruction Set Summary
(Data Transfer)
1. CBW ;Convert Byte to Word AL  AX
2. CWD ;Convert Word to Double in AX DX,AX
3. IN ;Input
4. LAHF ;Load AH from Flags
5. LDS ;Load pointer to DS
6. LEA ;Load EA to register
7. LES ;Load pointer to ES
8. LODS ;Load memory at SI into AX
9. MOV ;Move
10. MOVS ;Move memory at SI to DI
11. OUT ;Output
12. POP ;Pop
13. POPF ;Pop Flags
14. PUSH ;Push
15. PUSHF ;Push Flags
16. SAHF ;Store AH into Flags
17. STOS ;Store AX into memory at DI
18. XCHG ;Exchange
19. XLAT ;Translate byte to AL

(Arithmetic/Logical)
1. AAA ;ASCII Adjust for Add in AX
2. AAD ;ASCII Adjust for Divide in AX
3. AAM ;ASCII Adjust for Multiply in AX
4. AAS ;ASCII Adjust for Subtract in AX
5. ADC ;Add with Carry
6. ADD ;Add
7. AND ;Logical AND
8. CMC ;Complement Carry
9. CMP ;Compare
10. CMPS ;Compare memory at SI and DI
11. DAA ;Decimal Adjust for Add in AX
12. DAS ;Decimal Adjust for Subtract in AX
13. DEC ;Decrement
14. DIV ;Divide (unsigned) in AX(,DX)
15. IDIV ;Divide (signed) in AX(,DX)
16. MUL ;Multiply (unsigned) in AX(,DX)
17. IMUL ;Multiply (signed) in AX(,DX)
18. INC ;Increment

(Arithmetic/Logical Cont.)
19. NEG ;Negate
20. NOT ;Logical NOT
21. OR ;Logical inclusive OR
22. RCL ;Rotate through Carry Left
23. RCR ;Rotate through Carry Right
24. ROL ;Rotate Left
25. ROR ;Rotate Right
26. SAR ;Shift Arithmetic Right
27. SBB ;Subtract with Borrow
28. SCAS ;Scan memory at DI compared to AX
29. SHL/SAL ;Shift logical/Arithmetic Left
30. SHR ;Shift logical Right
31. SUB ;Subtract
32. TEST ;AND function to flags
33. XLAT ;Translate byte to AL
34. XOR ;Logical Exclusive OR

(Control/Branch)
1. CALL ;Call
2. CLC ;Clear Carry
3. CLD ;Clear Direction
4. CLI ;Clear Interrupt
5. ESC ;Escape (to external device)
6. HLT ;Halt
7. INT ;Interrupt
8. INTO ;Interrupt on Overflow
9. IRET ;Interrupt Return
10. JB/JNAE ;Jump on Below/Not Above or Equal
11. JBE/JNA ;Jump on Below or Equal/Not Above
12. JCXZ ;Jump on CX Zero
13. JE/JZ ;Jump on Equal/Zero
14. JL/JNGE ;Jump on Less/Not Greater or Equal
15. JLE/JNG ;Jump on Less or Equal/Not Greater
16. JMP ;Unconditional Jump

(Control/Branch Cont.)
17. JNB/JAE ;Jump on Not Below/Above or Equal
18. JNBE/JA ;Jump on Not Below or Equal/Above
19. JNE/JNZ ;Jump on Not Equal/Not Zero
20. JNL/JGE ;Jump on Not Less/Greater or Equal
21. JNLE/JG ;Jump on Not Less or Equal/Greater
22. JNO ;Jump on Not Overflow
23. JNP/JPO ;Jump on Not Parity/Parity Odd
24. JNS ;Jump on Not Sign
25. JO ;Jump on Overflow
26. JP/JPE ;Jump on Parity/Parity Even
27. JS ;Jump on Sign
28. LOCK ;Bus Lock prefix
29. LOOP ;Loop CX times
30. LOOPNZ/LOOPNE ;Loop while Not Zero/Not Equal
31. LOOPZ/LOOPE ;Loop while Zero/Equal
32. NOP ;No Operation (= XCHG AX,AX)

(Control/Branch Cont.)
33. REP/REPNE/REPNZ ;Repeat/Repeat Not Equal/Not Zero
34. REPE/REPZ ;Repeat Equal/Zero
35. RET ;Return from call
36. SEG ;Segment register
37. STC ;Set Carry
38. STD ;Set Direction
39. STI ;Set Interrupt
40. TEST ;AND function to flags
41. WAIT ;Wait

8086 Instruction set Summary

8086 Assembler Directives
1. end label end of program, label is entry point
2. proc far|near begin a procedure; far, near keywords specify
if the procedure is in different code segment
(far), or same code segment (near)
3. endp end of procedure
4. page set a page format for the listing file
5. title title of the listing file
6. .code mark start of code segment

8086 Assembler Directives
7. .data mark start of data segment
8. .stack set size of stack segment
9. db define byte
10. dw define word (2 bytes)
11. dd define double word (4 bytes)
12. dq define quadword (8 bytes)
13. dt define tenbytes
14. equ equate, assign numeric expression to a name

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