Lecture Notes - Microprocessor - Unit 1 - Microprocessor Architecture and its operation

Microprocessor and Micro Controller
Unit I
Microprocessor Architecture and its Operation
Prepared By
Dr. S.Murugan, Associate Professor
Department of Computer Science,
AlagappaGovernment Arts College, Karaikudi.
(Affiliated by AlagappaUniversity)
Mailid: muruganjit@gmail.com
Reference Book:
Microprocessor Architecture – Programming and Applications with 8085 – R. S. Gaonkar

Introduction - Microprocessor Architecture and
its Operation

Microprocessor
➢ The microprocessor is a programmable digital device,
designed with registers, flip-flops and timing element.
➢ It is a central processing unit (CPU) on a single
integrated circuit (IC) chip that performs arithmetic
and logic operations, data transfer, and control
operations.
➢ It acts as the brain of a computer or embedded system.

Microprocessor architecture
➢ Microprocessor architecture refers to the internal
structure and organization of components in a
microprocessor, including its registers, buses,
instruction set, and control unit, which collectively
determine how it processes data.
➢ The function of microprocessor can be classified into
three general categories;
(i) Microprocessor-initiated operations
(ii) internal operations
(iii) peripheral operations.

➢ To perform the above functions, the microprocessor
requires a group of logic circuits and a set of signals
called control signal.
➢ A control signal is an electrical signal generated by
the control unit of a microprocessor or computer
system to coordinate and control the operation of other
components, such as memory, input/output devices,
and the processor itself.

➢ The Central Processing Unit (CPU) and the Micro
Processor Unit (MPU) is related but not same. A CPU
can be implemented as a combination of more than
one chip.
➢ Whereas, the MPU refers a single chip processor. The
microprocessor and Micro Processor Unit often are
used synonymously.

Microprocessor initiated operations and Bus
Organization

Microprocessor initiated operations
➢ Microprocessor-initiated operations are tasks performed
by the microprocessor to communicate with memory and
peripherals, such as memory read, memory write, I/O read,
and I/O write operations.
➢ The MPU performs primarily four operations :
1. Memory Read : Reads data or instructions from memory.
2. Memory Write : Write data or instructions into memory.
3. I/O Read : Accepts data from input devices.
4. I/O Write : Sends data to output devices.

Microprocessor initiated operations
➢ To communicate with a peripheral or a memory
location, the MPU needs to perform the following
steps:
1. Identify the peripheral or the memory location (with
its address)
2. Transfer binary information (data and instruction)
3. Provide timing or synchronization signals.
The 8085 MPU performs these functions using three
sets of communication lines called buses: the address
bus, the data bus, and the control bus.

8085 Bus Organization
➢ The 8085 bus organization refers to the system of
buses used by the 8085 microprocessor to
communicate with memory, input/output devices,
and other components as shown in Figure 1.1.
➢ The 8085 microprocessor has three primary buses:
Address Bus, Data Bus, and Control Bus, each
serving a specific purpose in the microprocessor's
operation.

8085 Bus Organization
Fig. 1.1 The 8085 Bus Structure

Address Bus
➢ The address bus is a group of 16 lines generally
identified as A0 to A15.
➢ It is unidirectional (bits flow in one direction) from the
microprocessor to the memory or peripheral devices.
➢ The MPU uses the address bus to specify the memory
location or I/O device to be accessed.
➢ In the 8085 microprocessors, the address is 16 bits,
allowing access to 216=65,536 (64 KB) memory
locations.

Data Bus
➢ The data bus is a group of 8 lines generally identified
as D0 to D7.
➢ It is bi-directional (bits flow in both direction)
between the microprocessor and the memory or
peripheral devices.
➢ The data bus is used to transfer data between the
processor, memory, and I/O devices.
➢ The eight data lines enable the MPU to manipulate 8-
bit data ranging from 00 to FF (28 =256).

Data Bus
➢ The smallest number that can appear on the data bus
0000 0000 (00).
➢ The largest number that can appear on the data bus
1111 1111 (FF).
➢ so that the 8085 is known as an 8-bit microprocessor

Difference between Data Bus and Address Bus
S. No.Feature Data Bus Address Bus
1. Direction Bidirectional Unidirectional
2.
Purpose
Transfers data or
instructions
Carries memory/I/O
addresses
3. Size
(8085)
8 bits 16 bits
4 Functional
ity
Exchanges data
between components
Identifies memory or
I/O locations

Control Bus
➢ The control bus is comprised of various single lines
that carry synchronization signals.
➢ It is used to provide the timing or synchronization
signals.
➢ The control bus lines are not a group of lines like
address bus or data bus, the individual lines that
provide a pulse to indicate an MPU operation.
➢ The MPU generates control signals for every
operation (such as memory read or memory write
operations).

Control Bus
➢ The control bus carries control signals to coordinate
and manage communication between the processor,
memory, and peripherals. Important control signals
include:
o RD (Read): Indicates data is being read.
o WR (Write): Indicates data is being written.
o ALE (Address Latch Enable): Distinguishes
address and data on the same lines.
o IO/M: Differentiates memory and I/O operations.
The control bus ensures proper synchronization
during data transfer.

Control Bus - Example
➢ For Example the following instruction, the data 78 is
transferred into Register B.
2000 06 MVI B,78H
➢ Here 2000 is a memory location, 06 is a hex code for
immediate data transfer to Register B.
Fig. 1.2 Memory Read Operation

Control Bus - Example
➢ The following sequence of steps to be followed to read
an instruction from a memory location as shown in Fig
1.2.
1. 16 -bit address (2000) placed on the address bus.
2. The address is decoded by external logic circuit and
the memory location is identified.
3. MPU sends the memory read control signal (pulse).
4. The pulse activates the memory chip.
5. The contents of the memory location (8-bit data – 06)
placed on the data bus and brought inside the MPU.

Internal Data Operations and the 8085 Registers

Internal Data Operations
➢ Internal data operation in the 8085 microprocessor
refers to operations that manipulate data within the
microprocessor, using its internal registers and the
accumulator.
➢ These operations include arithmetic, logical, and data
transfer instructions that involve temporary storage
and processing without external memory access. For
example, adding two numbers, performing a logical
AND operation, or moving data between registers.
The accumulator and general-purpose registers are
primarily involved in these operations.

Internal Data Operations
➢ The internal architecture of the 8085 microprocessor
determines how and what operations can be performed
with the data. These operations are
➢ Store 8-bit data
➢ Perform arithmetic and logical operations.
➢ Test for conditions (Carry Flag).
➢ Sequence the execution of instructions
(Program Counter)
➢ Store data temporarily during execution in the
defined R/W memory locations called the stack.

8085 Registers
➢ To perform the above operations, the microprocessor
requires registers, an arithmetic/logic unit (ALU) ,
control logic and internal buses.
➢ The programming model of the 8085 displaying the
internal registers and accumulator as shown in the
figure 1.3.
Fig. 1.3 The 8085 Programmable Registers

8085 Registers
➢ The 8085 microprocessor has several programmable
registers that perform specific functions in data
handling and processing.
➢ Here's a concise explanation of each component:
➢ Accumulator (A): Stores results of arithmetic,
logical operations, and intermediate data.
➢ General Purpose Registers (B, C, D, E, H, L):
Used for temporary storage of data during
operations.
➢ Flag Register: Contains status flags (Z, S, P, CY,
AC) indicating conditions after operations.

8085 Registers
➢ Program Counter (PC): Holds the address of the
next instruction to be executed.
➢ Stack Pointer (SP): Points to the top of the stack,
used for subroutine calls and returns.
➢ Instruction Register (IR): Holds the current
instruction being decoded and executed.
➢ Temporary Register: Holds intermediate data
during execution, typically used for internal
operations.

Microprocessor function - Example program
➢ The following example program (addition of two
numbers) demonstrates the function of the
microprocessor.
➢ The hex codes of the program are stored in memory
locations from 2000 to 2005 as shown in Fig. 1.2.

Microprocessor function with Example program
Memory
Location
Hex
Code
Mnemonics Comments
2000 06 MVI B, 78H ; Transfer the value 78 into Register B.
2001 78
2002 3E MVI A, F2H ; Transfer the value F2 to Accumulator.
2003 F2
2004 80 ADD B ; The content of Register B is added with
Accumulator and the results are stored in
Accumulator.
2005 76 HLT ; Terminate the Program

➢ When executes the above instructions, the
microprocessor places the address 2000 into address
bus and increments the address in the PC (Program
Counter) to 2001 for the next operation. It brings the
code 06, interprets the code, places the address 2001
on the address bus, and then gets byte 78H and
increments the address in PC to 2002.
➢ The First two instruction is used to transfer the data
into register B and Register A.

➢ The third instruction ADD is used to perform the
addition operation and the result is stored into
accumulator. In this case 78 + F2 = 16AH, the
accumulator holds only the value 6A, the value 1
indicates the carry flag.
➢ The Fourth instruction terminates the program.

Peripheral or Externally Initiated Operation
➢ External devices can initiate the following operations :
Reset, Interrupt, Ready and Hold.
➢ Reset : When the reset pin is activated by external key
(reset key), all internal operations are suspended and
the program counter is cleared. Now, the program
execution can begin at the zero memory address.
➢ Interrupt : The microprocessor can be interrupted
from the normal execution of instructions and asked to
execute some other instructions called a service
routine. The microprocessor resumes its operation
after completing the service routine.

Peripheral or Externally Initiated Operation
➢ Ready : If the signal of this ready pin is low, the
microprocessor enters into a wait state.If it is high, the
microprocessor ready to send or receive data.
➢ Hold : When the HOLD pin is activated by an
external signal, the microprocessor relinquishes
control of buses and allows the external peripherals to
use them. For example, the HOLD signal is used in
Direct Memory Access (DMA) data transfer.

Difference between Microprocessor-initiated
operation and Peripheral-Initiated Operation
Feature Microprocessor-Initiated Peripheral-Initiated
Initiator Microprocessor External device (peripheral)
Examples
Memory Read, Memory
Write, I/O Read
Interrupts, Direct Memory
Access (DMA)
Control
Controlled by
microprocessor signals
Triggered by external signals
Priority Sequentially executed Can interrupt current operations
Execution
Part of the microprocessor
program flow
Requires special handling like
ISR

Lecture Notes - Microprocessor - Unit 1 - Microprocessor Architecture and its operation

Recommended

More Related Content

What's hot (19)

Similar to Lecture Notes - Microprocessor - Unit 1 - Microprocessor Architecture and its operation (20)

More from Murugan146644 (20)

Recently uploaded (20)

Lecture Notes - Microprocessor - Unit 1 - Microprocessor Architecture and its operation