Microprocessor vs. Microcontroller - Understand the Key Differences | Piest Systems

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Piest Systems is a pioneering institution dedicated to advancing knowledge in Embedded
Systems and Automotive Technologies. With a focus on providing high-quality training
programs, Piest Systems equips engineers, freshers, and working professionals with
essential skills in areas such as microcontroller programming, IoT integration, and
advanced communication protocols. Our courses are designed to meet industry
standards, ensuring participants are well-prepared for real-world challenges. Committed
to excellence, Piest Systems is ISO 9001:2015 certified and has been recognized with a
nomination for the India 5000 Best MSME Awards, underscoring our dedication to quality
education and professional development in the technology sector.
About the Piest Systems

EMBEDDED SYSTEMS
Embedded Systems - Overview
A system is an organized arrangement where all its components work together according
to established rules. It can be defined as a method of performing, organizing, or executing
one or more tasks based on a predefined plan. For instance, a watch functions as a time-
displaying system, with its parts operating under specific rules to indicate time. If any
component fails, the watch ceases to function. Therefore, it can be concluded that all
subcomponents within a system are interdependent, relying on one another to ensure
overall functionality.
System
As the name implies, "embedded" refers to something that is attached to another entity.
An embedded system can be understood as a computer hardware system with software
integrated into it. This type of system can function independently or serve as a
component within a larger system. Essentially, an embedded system is based on a
microcontroller or microprocessor and is designed to perform a specific task. For
instance, a fire alarm is an embedded system that detects smoke.
An embedded system comprises three main components:
Hardware
Application Software
Real-Time Operating System (RTOS): The RTOS manages the application software and
provides the framework for scheduling processes, controlling latencies, and ensuring
efficient execution of tasks. It defines how the system operates and establishes rules
for the execution of application programs. Smaller embedded systems may not utilize
an RTOS.
Embedded System

EMBEDDED SYSTEMS
In summary, an embedded system is a microcontroller-based, software-driven, reliable,
real-time control system.
Single-Functionality : An embedded system typically performs a specialized function
and executes it repeatedly. For example, a pager is dedicated solely to its primary
function of messaging.
Tightly Constrained : While all computing systems face design constraints, those for
embedded systems are often particularly strict. Design metrics, which measure
features such as cost, size, power consumption, and performance, must be optimized.
The system should be compact enough to fit on a single chip, fast enough to process
data in real-time, and energy-efficient to prolong battery life.
Reactive and Real-Time : Many embedded systems are designed to continuously
respond to changes in their environment and deliver results in real-time without
delays. For instance, a car's cruise control system constantly monitors speed and
brake sensors, calculating acceleration or deceleration within a strict timeframe.
Delayed computations in this context can compromise vehicle control.
Microprocessor-Based : Embedded systems rely on microprocessors or
microcontrollers for their operation.
Memory : They typically contain memory, as the software is often embedded in Read-
Only Memory (ROM). Secondary memory is generally unnecessary.
Connected : Embedded systems feature connected peripherals to interface with
input and output devices.
HW-SW Systems : They utilize software to enhance functionality and flexibility while
employing hardware to ensure performance and security.
Characteristics of an Embedded System

EMBEDDED SYSTEMS
ASIP & ASIC
PROCESSOR CORE
ANALOG I/O
DIGITAL I/O
MEMORY

EMBEDDED SYSTEMS
Advantage
Easily Customizable
Low Power Consumption
Low Cost
Enhanced Performance
Disadvantage
High development effort
Larger time to market
Basic Structure of an Embedded Systems
Sensor A-D
Converter
Processor &
ASIC
D-A
Converter Actuator
Memory

EMBEDDED SYSTEMS
Sensor : A sensor detects a physical quantity and converts it into an electrical signal,
which can be read by an observer or processed by an electronic device, such as an
Analog-to-Digital (A2D) converter. It also stores the measured value in memory.
A-D Converter : The Analog-to-Digital converter transforms the analog signal from
the sensor into a digital signal that can be processed.
Processor & ASICs : The processor analyzes the digital data, calculates the output,
and stores the result in memory.
D-A Converter : A Digital-to-Analog converter converts the digital output from the
processor into an analog signal.
Actuator : The actuator compares the analog output from the D-A converter to the
expected value, then stores and applies the approved result.

EMBEDDED SYSTEMS
Embedded System - Processors
The processor is the core of an embedded system, acting as the fundamental unit that
receives inputs, processes the data, and generates the output. For an embedded system
designer, understanding both microprocessors and microcontrollers is essential to
effectively design and optimize the system's performance.
A processor consists of two key components:
Program Flow Control Unit (CU)
Execution Unit (EU)
The CU contains a fetch unit responsible for retrieving instructions from memory. The
EU houses circuits that carry out instructions related to data transfer and data
conversion between different forms. It also includes the Arithmetic and Logical Unit
(ALU), as well as circuits that handle program control tasks like interrupts or jumps to
different instruction sets.
The processor operates in a cycle, fetching and executing instructions in the same
order they are retrieved from memory.
Processor in a System

EMBEDDED SYSTEMS
Processors can be categorized as follows:
General Purpose Processors (GPP):
Microprocessor
Microcontroller
Embedded Processor
Digital Signal Processor (DSP)
Media Processor
Application Specific System Processor (ASSP)
Application Specific Instruction Processors (ASIPs)
GPP Core(s) or ASIP Core(s) integrated into an Application Specific Integrated Circuit
(ASIC) or a Very Large Scale Integration (VLSI) circuit.
Types of Processors

EMBEDDED SYSTEMS
A microprocessor is a single VLSI chip having a CPU. In addition, it may also have other
units such as coaches, floating point processing arithmetic unit, and pipelining units that
help in faster processing of instructions. Earlier generation microprocessors’ fetch-and-
execute cycle was guided by a clock frequency of order of ~1 MHz. Processors now
operate at a clock frequency of 2GHz
Microprocessor
CPU
Genearl
Purpose
Microprocesoor
RAM ROM
I/O
PORT
TIMER
SERIAL
COM
PART
A Simple Block Diagram Of Microprocessor

EMBEDDED SYSTEMS
A microcontroller is a single-chip Very Large Scale Integration (VLSI) device, often referred
to as a microcomputer. While it has limited computational power, it offers enhanced
input/output capabilities and includes several on-chip functional units, making it highly
versatile for various embedded applications.
Microcontroller
CPU RAM ROM
I/O
PORT
TIMER
SERIAL
COM PORT
Microcontroller Chip

EMBEDDED SYSTEMS
Let us now take a look at the most notable differences between a microprocessor and a
microcontroller.
Microcontroller VS Microcontroller
Microprocessor Microcontroller
Microprocessors are designed for
multitasking, allowing them to perform
multiple tasks simultaneously. For
instance, on a computer, you can play
music while typing in a text editor.
RAM, ROM, I/O ports, and timers can be
added externally and their quantities
can vary depending on the system's
requirements.
Designers have the flexibility to
determine the required number of
memory units or I/O ports.
The addition of external memory and
I/O ports increases the complexity and
cost of a microprocessor-based
system.
External devices take up more space
and have higher power consumption.
Single-task oriented systems are
designed to perform one specific
function. For example, a washing
machine is built solely for washing
clothes.
RAM, ROM, I/O ports, and timers
cannot be added externally. These
components are embedded together
on a chip with fixed quantities
A fixed amount of memory and I/O
makes a microcontroller well-suited
for performing specific, limited tasks
efficiently.
Microcontrollers are more
lightweight and cost-effective
compared to microprocessors.
A microcontroller-based system is
more power-efficient and occupies
less space.

EMBEDDED SYSTEMS
Embedded System - Architecture
The 8051 microcontrollers operate with an 8-bit data bus, allowing them to support
external data memory and external program memory of up to 64K each. In total, the 8051
microcontrollers can address 128K of external memory. When data and code are stored in
separate memory blocks, the architecture is known as Harvard architecture. Conversely,
when both data and code are located in the same memory block, it is referred to as Von
Neumann architecture.
Von Neumann Architecture
The Von Neumann architecture, proposed by computer scientist John von Neumann,
features a single data path or bus for both instructions and data. Consequently, the CPU
can perform only one operation at a time; it either fetches an instruction from memory or
carries out a read/write operation on data. This means that instruction fetching and data
operations cannot occur simultaneously, as they share the same bus.
It features a single memory space that stores both data and program instructions,
allowing for sequential execution. This architecture facilitates a simple and efficient
design, but it can also lead to bottlenecks, known as the "Von Neumann bottleneck," due
to the shared bandwidth between data and instructions.

EMBEDDED SYSTEMS
Program
ROM
Variable
RAM
Stack
RAM
Data
Addr
ctrl
Memory
Interface
Unit
Processor
and Built in
Register
Instruction Decode
Figure: Von-Neumann Architecture

EMBEDDED SYSTEMS
Harvard Architecture
The Harvard architecture features distinct storage and signal buses for instructions and
data. In this architecture, data storage is entirely located within the CPU, preventing
access to instruction storage as if it were data. Computers utilizing this architecture
have separate memory areas for program instructions and data, enabling simultaneous
access to both.
Programs had to be loaded by an operator, as the processor was unable to boot itself. In
the Harvard architecture, it is unnecessary for the two types of memory to share
characteristics.

EMBEDDED SYSTEMS
Control Space
Program
ROM
Instruction
Decode
PC Stack
Processor & Register
Interface
Data
Addr
Ctrl
Data
Addr
Ctrl
Register
Space
Figure: Harvard Architecture

EMBEDDED SYSTEMS
Von-Neumann Architecture vs Harvard Architecture
The following points distinguish the Von Neumann Architecture from the Harvard
Architecture.
Von-Neumann Architecture Harvard Architecture
A single memory space is utilized to store
both code and data.
Processor needs to fetch code in a
separate clock cycle and data in another
clock cycle. So it requires two clock cycles.
Higher speed, thus less time consuming.
Simple in design.
Separate memories for code and data.
Single clock cycle is sufficient, as
separate buses are used to access code
and data.
Slower in speed, resulting in increased
time consumption.
Complex in design.

EMBEDDED SYSTEMS
CISC and RISC
CISC (Complex Instruction Set Computer) and RISC (Reduced Instruction Set Computer)
are two different architectures used in computer design, each with its own
characteristics and advantages.
CISC (Complex Instruction Set Computer)
Definition : CISC architecture is designed to execute a large number of instructions,
allowing for more complex operations within a single instruction.
Instruction Set : It has a rich instruction set, which can perform multiple tasks in a
single instruction, such as loading data from memory, performing arithmetic
operations, and storing results.
Examples : Common examples of CISC architectures include the x86 family of
processors.
Advantages :
Compact Code : Since each instruction can perform multiple operations, programs
tend to have smaller code sizes.
Complex Operations: It can handle complex tasks without requiring many
instructions.
Disadvantages :
Slower Execution: The complexity of the instructions can lead to slower
execution times due to longer decoding and execution cycles.
Higher Power Consumption: The more complex circuitry can consume more
power.

EMBEDDED SYSTEMS
RISC (Reduced Instruction Set Computer)
Definition : RISC architecture focuses on a smaller set of simpler instructions,
designed to be executed in a single clock cycle.
Instruction Set : It uses a limited number of instructions, typically of a fixed length,
emphasizing efficiency and speed.
Examples : Examples include ARM, MIPS, and PowerPC architectures.
Advantages :
Faster Execution: Simpler instructions can be executed more quickly, often in one
clock cycle, leading to better performance.
Lower Power Consumption: Less complex circuitry generally results in lower
power consumption.
Disadvantages :
Larger Code Size : Programs may require more instructions to perform the same
task, resulting in larger code sizes.
More Compiler Work : Requires advanced compilers to optimize the use of the
limited instruction set effectively.

EMBEDDED SYSTEMS
CISC and RISC
RISC
Larger set of instructions. Easy to program.
Simpler design of compiler, considering larger
set of instructions.
Many addressing modes causing complex
instruction formats
Instruction length is variable.
Higher clock cycles per second.
Emphasis is on hardware.
Control unit implements large instruction set
using micro-program unit.
Slower execution, as instructions are to be
read from memory and decoded by the
decoder unit.
Pipelining is not possible.
Smaller set of Instructions. Difficult to
program.
Complex design of compiler.
Few addressing modes, fix instruction format
Instruction length varies.
Low clock cycle per second.
Emphasis is on software.
Each instruction is to be executed by
hardware.
Faster execution, as each instruction is to be
executed by hardware.
Pipelining of instructions is possible,
considering single clock cycle.
The following points differentiate a CISC from a RISC –
CISC

EMBEDDED SYSTEMS
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Website : www.piestsystems.com

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