An Introduction to the 80x86 Microprocessor Family

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Chapter 2
EE314Microprocessor Systems

• An Introduction to the 80x86 Microprocessor Family

Objectives Real-mode and protected-mode
operation The register set of 80x86 family The
addressing capabilities and data types that may
be used
Based on "An Introduction to the Intel Family of
Microprocessors" by James L. Antonakos
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2.2 Real mode and Protected mode operation

• Addressable memory

• 8086 20 address lines gt 1MB (Mega Byte)
• Pentium 32 address lines gt 4096MB

For compatibility, all the 80x86 family members
start running in Real Mode, emulating the 8086
features (i.e. 1MB RAM) Beginning with 80286, the
Protected Mode is also available, allowing
direct control of all address lines (all
addressable memory), multitasking support,
virtual memory addressing, memory management and
protection (against violation from other task),
control over internal data and instruction cache.
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2.3 The Software Model of 80x86 Family
15 . . . 8,7 . . . 0
15 . . . 8,7 . . . 0
31 . . . . . . 16,15 . . . 8,7 . . . 0
Accumulator Base Count Data Base Pointer Source
Index Destination Index
Code Segment Data Segment Stack Segment Extra
Segment
Extended registers, only on 80386 and higher CPUs
FS GS
Instruction Pointer Stack Pointer Flags
32 bit registers, 80386 or higher only
8 bit registers
16 bit registers
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2.4 Processor Registers
15 . . . 8,7 . . . 0
A prefix (66H) allows using 32 bit registers in
the real mode db 66h EAX instead AX mov
ax,1140h less significant 16 bits db
058bh most significant 16 bits
Multiply, divide, accessing I/O... Counter in
loop operations Multiply, divide, pointer to
I/O... Source index in string operations... Desti
nation index in string operations
Accumulator Base Count Data Base Pointer Source
Index Destination Index
Segment a 64kbyte memory block beginning at a
multiple by 10H address.
Code Segment Data Segment Stack Segment Extra
Segment
Shift to left 4 bits
An effective address is generated as combination
between a segment register and another register
as in the example.
16 bit
FS GS
A000 5F00 A5F00
Add
Each segment register has a default usage (class
of instructions where apply).
16 bit
Pointer in program flow Pointer in Stack Control
and status flags
Instruction Pointer Stack Pointer Flags
Effective Address (20bits)
16 bit registers
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2.4 Processor RegistersFlag register
CF PF AF ZF SF TF IF DF OF IOPL NT
Carry Flag Parity Flag Auxiliary carry Flag Zero
Flag Sign Flag Trace Flag Interrupt enable
Flag Direction Flag Overflow Flag I/O Priority
Level Nested Task
Contains Carry out of MSB of result Indicates if
result has even parity Contains Carry out of bit
3 in AL Indicates if result equals zero
Indicates if result is negative Provides a
single step capability for debugging Enables/disab
les interrupts Controls pointer updating during
string operations Indicates that an overflow
occurred in result Priority level of current task
(two bits) Indicates if current task is nested
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2.5 Data OrganizationBits, Bytes, Words,
Double-words
Possible Values Binary Hexadecimal Decimal 0,1
0,1 0,1 0...1111 0...F 015 01111,1111 0FF
0255 0(16 1s) 0FFFF 065,535 0(32
1s) 0FFFFFFFF 0...4,294,967,295
Name Bit Nibble Byte Word Double Word
Size BInary digiT 4 bits 8 bits 16 bits 2
bytes 32 bits 4 bytes
Byte swapping if a word has to be stored into an
8 bit wide memory at address adr, its low byte is
stored at adr and its high byte at adr1. If a
word is read from an 8 bit memory at address adr,
the low byte is loaded from adr and the high byte
from adr1. Rule low significance ltgt low
address
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2.5 Data OrganizationAssembler directives DB,
DW, DUP and EQU.
Define Byte reserves memory for a byte and assign
to it the specified value.
... 0003 0D 0004 30 0005 C8 0006 3A 0007
CE ...
Decimal, binary, octal or hexadecimal numbers can
be used.
Example 0000 .DATA 0000 03 NUM1 DB 3 0001
04 NUM2 DB 100B 0002 00 NUM3 DB ? 0003 0D
30 C8 3A CE NUMS DB 15O,48,200,3AH,0CEH 0008 48
69 24 MSG DB Hi 000E 0006 WX DW 6 0010
03E8 WY DW 1000 0012 1234 ABCD
WZ DW 1234H,0ABCDH 0016 0000 TEMP DW ? 0018
000A 00 SRS DB 10 DUP(0) 0022 0007 0000
TIME DW 7 DUP(?) 000D TOP EQU 13 157C
MORE EQU 5500
A list of values can be used.
A character string generates the associate
ASCII bytes
Similarly, Define Word reserves memory space for
a word and assign to it the specified value.
Byte swapping 0012 34 0013 12 0014 CD 0015
AB ...
A numerical value begins with a decimal digit, or
a non-significant 0 is added
Duplicate repeats n times the value between ( ).
Equate directive assign a value to a constant
without memory space reservation.
A label is assigned the address of the first byte
involved in its statement.
A ? reserves memory space without assigning
values.
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2.6 Instruction typesData transfer instructions
8086 instruction set IN Input byte or word from
port LAHF Load AH from flags LDS Load pointer
using data segment LEA Load effective
address LES Load pointer using extra
segment MOV Move to/from register/memory OUT Outpu
t byte or word to 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
Additional 80386 instructions LFS Load pointer
using FS LGS Load pointer using GS LSS Load
pointer using SS MOVSX Move with sign
extended MOVZX Move with zero extended POPAD
Pop all double (32 bit) registers POPD Pop
double register POPFD Pop double flag register
PUSHAD Push all double registers PUSHD Push
double register PUSHFD Push double flag register
Additional 80486 instruction BSWAP Byte swap
Additional 80286 instructions INS Input string
from port OUTS Output string to port POPA Pop all
registers PUSHA Push all registers
Additional Pentium instruction MOV Move to/from
control register
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2.6 Instruction typesArithmetic instructions
8086 instruction set 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 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 Negat
e byte or word SBB Subtract byte or word and
carry (borrow) SUB Subtract byte or word
Additional 80386 instructions CDQ Convert
double-word to quad-word CWDE Convert word to
double-word
Additional 80486 instructions CMPXCHG
Compare and exchange XADD Exchange
and add
Additional Pentium instruction CMPXCHG8B
Compare and exchange 8 bytes
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2.6 Instruction typesBit manipulation
instructions
8086 instruction set 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
Additional 80386 instructions BSF Bit scan
forward BSR Bit scan reverse BT Bit test BTC Bit
test and complement BTR Bit test and
reset BTS Bit test and set SETcc Set byte on
condition SHLD Shift left double
precision SHRD Shift right double precision
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2.6 Instruction typesString instructions
8086 instruction set CMPS Compare byte or word
string LODS Load byte or word
string MOVS Move byte or word
string MOVSB(MOVSW) Move byte string (word
string) REP Repeat REPE (REPZ) Repeat while
equal (zero) REPNE (REPNZ) Repeat while not
equal (not zero) SCAS Scan byte or word
string STOS Store byte or word string