Electrical Engineering Department
Engineering College
Prince Sattam bin Abdul Aziz University
Text Book:
- Triebel and Singh, "The 8088 and 8086 Microprocessors",
Prentice Hall, Last Edition.
Course Grading:
Midterm # 1
Midterm # 2
Reports & Projects
Lab Performance
Final Exam
:
:
:
:
:
(20%)
(20%)
(10%)
(10%)
(40%)
Course Plan
Microprocessor architecture
 Instruction sets
Assembly language programming and debugging
Input and Output Interfacing
Interrupt controller interfacing
Project. Micro-controllers
Introduction
 Microprocessors
touch nearly every aspect of
our lives. Just a few of the products which use
microprocessors are:
 Cameras
 Calculators
 Automobiles
 Electronic Toys
 Electronic Credit Card Machines
 Microwave Ovens
What is a microprocessor?
Microprocessors are small electronic devices which
manipulate and control digital data with great speed and
accuracy.
Typically, they are about 3 to 4 inches long and about 1
inch wide.
Figure . Microprocessor
Computer Basics
1. INPUT: Provides information from the outside
world, acting as the eyes and ears of the computer
system.
2. CONTROL: Directs the overall functioning of the
computer. All information must pass through the
control during its processing.
3. MEMORY: Supplies temporary storage for
information to be processed and permanent storage
for program instructions.
4. A.L.U.: The Arithmetic Logic Unit is the actual
calculating mechanism, where operations are
performed on the information that is input.
5. OUTPUT: Delivers the processed information to the
outside world.
Figure . Fundamental Microcomputer
Basic Microprocessor Operations
Objectives:
 How memory locations are addressed
 How data is stored
 5 basic internal registers
Introduction
 Computer buses:
 Address bus (carries location details),
 Control bus (carries timing and enable/disable signals),
 Data bus (carries instructions and information to be
processed).
 CPU receives the signals and operates upon them
 How the microprocessor uses these signals to perform its
required tasks?
Operational Process
 Memory contains many locations for
data or instructions.
 Each location has a unique address.
 We access a location by :
 sending the location's address to the
memory section and enabling READ
(get from) or WRITE (send to).
 The microprocessor then gets the data stored at that address or it
moves data into that location.
Operational Process
 Memory capacity: measured by the number of bytes it
can hold.
 Recall that: control section a word to memory, it must
provide the memory with the address where the word is
to go. Ex. Emailing Address
 In a computer, this address is sent by transmitting an
additional one or two words to the memory section.
Internal Registers
 Where to find the data?
 What to do with the results?
 Internal Registers:

Status (Flag) Register

General Purpose Registers

Address Registers

Program Counter

Stack Pointer
Status (Flag) Registers
 Used to store a binary word
representing the status of ALU
 Each bit (or flag) of the status
register represents a specific
condition.
Bit #7 and #6 (U): Unused
Bit #5 (C): Carry Flag - Set when there is a carry of the MSB
Bit #4 (O): Overflow Flag - Set if the result is out of range
Bit #3 (Z): Zero Flag - Set if the result = 0
Bit #2 (N): Negative Flag - Set if the result is negative
Bit #1 (I): Interrupt Flag - Set if Interrupt is enabled
Bit #0 (P): Parity Flag - Set if the result has even parity (if there are an even number of 1's in the
result)
General Purpose (GP) Registers
 Required for processors to operate as fast as they do.
 Accumulator is a general purpose register which the ALU often
uses as the default location for an operand.
General Purpose (GP) Registers
 GP registers store one data word
 Each 8-bit Mic. have 8-bit GP registers
 Typically, each Pair register is named with a letter, for instance,
"register A", "B", or "C".
 Individual one-word registers named
 "register AL" (low word of register pair A)
 or "register AH" (high word of register pair A).
Address Registers
 Twice the length of the microprocessor's word size.
 Connected to the address bus and access the location of
data in memory.
 Address is stored in an address register
 Used by the control unit whenever data is moved to or from
the address.
Program Counter (PG)
 Contains the address of the next instruction to be
executed.
 PG begins at the memory address (e.g., 00010001) and
then increments to the next address (i.e., 00010010)
when the instruction in the first location has been
executed.
 The process repeats until the program re-directs the
program counter or terminates.
Stack Pointer
 Automatically adjusts to the next available (empty) location
in the stack, which is a block of memory that stores data.
 One format of storage is FILO (First In, Last Out)
 The stack pointer indicates which data is to be accessed
for correct execution of the program.
Computer Instructions
An instruction consists of a mnemonic (which the
human operator understands) and its binary code (which
the computer actually uses).
Examples of mnemonics:
 MOV (for "move"), ADD (for "add"), SUB (for
"subtract"), CMP (for "compare"), and JMP (for "jump").
Architectures of 8080A and 8086
Microprocessors
 Objectives:
 Describe the major components of the 8080A microprocessor.
 Describe the major components of the 8086 microprocessor.
 Discuss the differences between the 8080A and the 8086
microprocessors
8080A MICROPROCESSORS
 The 8080A is an 8-bit
microprocessor.
 Means that:
 its data bus and ALU
are 8-bits.
 Address Registers 16 bits.
Data Bus
Ports
Address
bus
Ports
8080A MICROPROCESSORS
 Accumulator :
8 bits,
 Program counter :
16 bits,

Flag register :
5 bits.
8080A Mic. (Internal Registers)
 Flag Register:
 The 8080A's flag register is 8 bits wide and gives the
status of 5 different conditions.
1- Carry Flag (CY) - Set by carry out of bit 7 (MSB)
2- Zero Flag (Z) - Set if result equals zero
3- Sign (S) - Set for positive numbers
4- Parity (P) - Set if even parity (even number of ones)
5- Auxiliary Carry (AC) - Set if carry out of bit 3 (used in BCD
arithmetic)
8080A MICROPROCESSORS
 General Purpose (GP) Registers:
 Six 8-bit GP registers.
 These registers can be paired to form three 16-bit registers.
 The register pairs are B&C, D&E, and H&L.
 Address Register:
 Contains the address of the memory location or I/O device to be
enabled.
 This register is 16 bits wide.
 This means that the 8080A can access up to 64 KB (2^16) of
memory.
8080A MICROPROCESSORS
 Program Counter:
 contains the address of the next instruction to be executed.
 same width (16 bits) as the address register
 Stack Pointer:
 The stack can be located any place in memory. Therefore,
the stack pointer must be able to locate any place in memory.
Because the memory is 64 KB, the stack pointer is 16 bits
wide.
8080A MICROPROCESSORS
 8080A INTERNAL BUS SYSTEM:
 Data Bus:
 8 bits wide.
 transmits information
(data or instructions) to
and receives information
from any specified device.
 Address Bus :
16-bit
 select one memory location or I/O device.
 Control Bus :
 synchronizes and
enables the devices and operations
Figure . Block Diagram of the 8086
8086 Microprocessor
 The lowest 16 bits of this port
act as both the data bus port
and the address bus port.

The highest 4 bits are
dedicated to the address bus.
 The I/O port has sequential pin
numbers.
Figure. The 8086 I/O Port
8086 Microprocessor
Figure . Block Diagram of the 8086
8086 Microprocessor
 ALU:
 Unlike the 8080A, the ALU in the 8086 can work directly with any
register or memory location.
 Means that: nearly all arithmetic and logic instructions (except
division) can be performed without first loading the accumulator with
one of the operands, as is required in the 8080A.
 8080A INTERNAL BUS SYSTEM:
 The 8086 uses one bus for both the data and address buses.
8086 Microprocessor:Flag Registers:
 16 flag registers available in the 8086. Nine flags are used: six status flags and
three control flags.
 Status Flags
1- Carry Flag (CF): Set when there is a carry out of the high order bit (8 or 16
bit) of the result.
2- Parity Flag (PF): Set if result contains an even number of 1's.
3- Auxiliary Carry Flag (AF): Set when there is a carry out of the low nibble.
4- Zero Flag (ZF): Set if the result equals zero.
5- Sign Flag (SF): Set if the result is a negative number.
6- Overflow Flag (OF): Set if the size of the result exceeds the size of the ALU.
8086 Microprocessor:Flag Registers:
 Control Flags:
 Trap Flag (TF)
 Interrupt Flag (IF)
 Direction Flag (DF)
8086 Microprocessor: General Purpose (GP) Registers:
 The 8086 contains four 16-bit GP registers named AX (accumulator),
BX, CX, and DX.
 Each of these registers can be split into its High (H) and Low (L) byte
to form eight 8-bit registers named AL, AH, BL, BH, and so on.
Figure. General Purpose Registers in the
8086
8086 Microprocessor: General Purpose (GP) Registers:
The 8086 also contains pointer, segment, and index
registers.
The Instruction Pointer :
 Points to the next instruction to
be executed.
 This register is similar to the
8080A's program counter.

8086 has a 20-bit address bus
Segment Registers is required.
Figure . Pointer and Segment Registers
in the 8086
8086 Microprocessor: General Purpose (GP) Registers:
 Code Segment register :
in combination with the instruction pointer allows the entire memory to be
addressed.
 Index registers :
used for various types of addressing.
Because the 8086 has a 20-bit address bus, it can access up to 1 MB (220) of
memory.
SUMMARY
 The major parts of a typical microprocessor are:




Control
ALU
Internal registers
I/O Ports
 The 8080A is
 an 8-bit microprocessor




an 8-bit flag Register,
an 8-bit ALU,
a16-bit address bus,
an 8-bit data bus.
 The 8086 is




a 16-bit microprocessor
a 16-bit flag register
a 16-bit ALU.
Its 20-bit address bus shares 16 bits with the data bus.
SUMMARY
 Internal registers of the 8080A include:
 ALU, accumulator, flag register, GP registers, address register,
program counter, and stack pointer.
Internal registers of the 8086 include:
ALU, flag register, GP registers, instruction pointer, code
segment register, and index registers.
 The flag register of the 8080A uses 5 of its 8 bits:
 Carry flag, zero flag, sign flag, parity flag, and auxiliary
carry flag.
SUMMARY
 The flag register of the 8086 uses 9 of its 16 bits:
 6 are status flags (parity flag, auxiliary carry flag, zero
flag, sign flag, and overflow flag)
3 control flags (trap flag, interrupt flag, and direction
flag).
 Both the 8080A and the 8086 microprocessors have 3
buses: data bus, address bus, and control bus.
 The 8080A ALU always works with the accumulator.