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UNIT-1 INTRODUCTION TO 8086 ECE DEPARTMENT
MICROPROCESSORS AND MICROCONTROLLERS Page 1
UNIT-I
INTRODUCTION TO 8086
Contents at a glance:
 Architecture of 8086 microprocessor
 Register organization
 8086 flag register and its functions
 Addressing modes of 8086
 Pin diagram of 8086
 Minimum mode & Maximum mode system operation
 Timing diagrams
INTRODUCTION TO MICROPROCESSOR:
OVERVIEW OF A SIMPLE MICRO COMPUTER:
The major parts are the central processing unit or CPU, memory, and the input and output circuitry or I/O.
Connecting these parts together are three sets of parallel lines called buses. The three buses are the address bus, the
data bus, and the control bus.
Block diagram of simple computer or microcomputer.
i) MEMORY: The memory section usually consists of a mixture of RAM and ROM. It may also have magnetic floppy
disks, magnetic hard disks, or laser optical disks. Memory has two purposes. The first purpose is to store the binary
codes for the sequence of instructions you want the computer to carry out. When you write a computer program,
what you are really doing is just writing a sequential list of instructions for the computer. The second purpose of the
memory is to store the binary-coded data with which the computer is going to be working.
ii) INPUT/OUTPUT: The input/output or I/O section allows the computer to take in data from the outside world or
send data to the outside world. These allow the user and the computer to communicate with each other. The actual
physical devices used to interface the computer buses to external systems are often called ports.
iii) CPU: The central processing unit or CPU controls the operation of the computer. It fetches binary-coded
instruction of the computer. It fetches binary-coded instructions from memory, decodes the instructions into a series
of simple actions, and carries out these actions. The CPU contains an arithmetic logic unit, or ALU. Which can perform
add, subtract, OR, AND, invert, or exclusive-OR operations on binary words when instructed to do so. The CPU also
contains an address counter which is used to hold the address of the next instruction or data to be fetched from
memory, general-purpose registers which are used for temporary storage of binary data, and circuitry which generates
the control bus signals.

UNIT-1 INTRODUCTION TO 8086 ECE DEPARTMENT
MICROPROCESSORS AND MICROCONTROLLERS Page 2
iv) ADDRESS BUS: The address bus consists of 16, 20, 24, or more parallel signal lines. On these lines the CPU sends
out the address of the memory location that is to be written to or read from. The number of address lines determines
the number of memory locations that the CPU can address. If the CPU has N address lines then it can directly address
2
N
memory locations.
v) DATA BUS: The data bus consists of 8, 16, 32 or more parallel signal lines. As indicated by the double-ended arrows
on the data bus line, the data bus lines are bi-directional. This means that the CPU can read data in on these lines