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By: Dr. Vikas Mahor
Department of Electronics Engineering
Introduction to Embedded System

What is an Embedded System?
 Embedded : means hidden inside so one can’t see it .
 System : means multiple components interfaced together
for
Doing specific task.
 Embedded System : is a special-purpose computer
system designed to perform certain dedicated functions.
 Functionalities : are done by dedicated HW and SW
with limited resources.
 On average, a person interacts with 100s of embedded
systems on daily basis.

Embedded Systems - Examples
• Any PC Mouse,
Keyboard, or USB
Device.
• Microcontroller:
8-bit.

• Any Disk Drive has
an embedded
Microcontroller
• Any Printer has an
embedded
Microcontroller

• Product: Creative Labs
Zen Vision:MVideo &
MP3 Player.
• Microcontroller: TI
TMS320 DSP.
• Canon EOS 30D Digital
Camera.
• DIGIC II Image
Processor.

• NASA's Twin Mars
Rovers.
• Microprocessor:
Radiation Hardened
20MHz PowerPC From
IBM
• Commercial Real-time
OS.
• Software and OS was
developed during multi-
year flight to Mars and
downloaded using a
radio link.

• Agilent Oscilloscope.
• Microprocessor: X86.
• OS: Windows XP.
• Product: Atronic Slot
Machine.
• Microprocessor: X86.
• OS: Windows CE.

• Sphero BB-8
• ARM Cortex-M4 core 32bit From ST

Sphero BB-8 From inside

• BMW 745i
• Windows CE OS.
• 53 8-bit µP.
• 11 32-bit µP.
• 7 16-bit µP.
• Multiple Networks.

• Sony Aiborobotic
dog.
• Microprocessor:
64-bits MIPS
RISC.

Computer Hardware
Microprocessor
A Large Memory:
(Primary & Secondary)
(Ram ,Rom ,Cache)
Input Units:
(Mouse,
Keyboard ,Scanner ,et
c.)
Output Units:
(Monitor ,Printer ,etc.)
I/O Units:
(FAX ,Ethernet,etc.)
Storage Units:
(Hard disk.)

Embedded System Hardware
Microcontroller which contain :
Processor, Timers, Interrupt controller, I/O Devices, Memories, Ports, etc.
All on Single Chip Or System On Chip (SOC).

Microprocessor Microcontroller
Higher Clock speed Slower clock speed
CPU is stand-alone, RAM,
ROM, I/O, timer are separate
CPU,RAM, ROM, I/O and timer
are all on a single chip
Designer can decide on the amount
of ROM, RAM and I/O ports
Fix amount of on-chip ROM,
RAM, I/O ports
Expansive Cheap
General-purpose Single-purpose
High Access time for memory Low Access time for memory
Very High power Low power

CPU
Architectures
1) Princeton Architecture (Von Neumann Architecture) :
Between 1945 & 1951 John von Neumann set down the structure,
layout, interaction, cooperation, realization , implementation,
functionality and activity for the whole computer as a system. The Von
Neumann Architecture is characterized by: -
 A memory, arithmetical-logical unit (ALU), control unit, input and
output device…. etc.
 All parts of a computer are connected together by Bus.
 Memory and Devices are controlled by CPU .
 Data can pass through bus in half duplex mode to and from CPU.
 Memory is split to small cells with the same size. Their ordinal numbers
are
called address numbers.
 Each time CPU fetches a program instruction it may have to perform one or
more read/write operation “instruction” from/to data memory space. It must
wait until these subsequent “instruction“ are complete before it can fetch

CPU
Architectures
Princeton Architecture (Von Neumann Architecture) :

CPU
Architectures
2) Harvard Architecture:
The Harvard Mark II was finished at Harvard University in 1947 . It
wasn’t so modern as the computer from von Neumann team. But it
introduced a slightly different architecture. Memory for data was
separated from the memory for instruction. This concept is known as
the HarvardArchitecture :
 There is no need to make the two memories share characteristics. In particular,
the word width, timing, implementation technology, and memory
address structure can differ.
 The CPU can read an instruction and perform a data memory access at the same
time..
 This speeds up execution time but increases the cost of more hardware
complexity.
 If, for instance, every instruction run in the CPU requires an access to memory, the
computer gains nothing for increased CPU speed—a problem referred to as being
"memory bound".

CPU
Architectures
Harvard Architecture:

Harvard Von Neumann
Used in DSPs and other processors
found in latest embedded systems and
Mobile communication systems, audio,
speech, image processing systems
Used in conventional processo rs
found in PCs and Servers, and
embedded systems with only
control functions.
Control unit for two buses is more
complicated and more expensive
One bus is simpler for the
control unit design
The code is executed in parallel The code is executed serially
and takes more clock cycles
Avg computation speed is high Avg computation speed is low

CPU
Architectures
Which is the best ?
For Processors :
Von Neumann is used in Processors because, unlike MCUs, processors don’t have
internal memory or peripherals and the connection to memory is through external
bus and Von Neumann is suitable because:
 Cost: less buses means less cost.
 Space: we don’t need to waste large space of motherboard.
 Processors mainly deal with only one memory, RAM which holds the
data and instructions, so only one bus will be suitable and the slow
access will be substituted by the high speed of the processor and
using the cash memory.
For Microcontroller :
Harvard architecture is used in MCU because:
 Microcontroller contains everything on the chip. RAM, flash, and
peripherals and due to the small size using multiple
buses is not an issue.
 Microcontroller speed is not high so multiple buses will help with
the limited speed of MCU.

CPU Structure
The basic elements of the CPU are:
• ALU
 Arithmetic & Logic Unit
 Responsible for performing logic and arithmetic
calculations.
• Floating-Point Unit (FPU)
 performs arithmetic operations on floating point
numbers.
• Registers
 Registers are used to store data beside the ALU
 Registers are used to transfer data to/from
memory
 Registers carry the inputs of ALU, as well as,
receiving the output of the ALU.
• Internal CPU Bus
 It is a special bus.
 It is responsible for transferring data between
registers, ALU, and system memory
• Control Unit
 It is responsible for organizing the actions of the CPU
 It can be thought of as the heart of the CPU

CPU Structure
Arithmetic logic unit :
• ALU is a digital circuit that performs :
 Arithmetic operations :
o Add, Sub,….etc.
 Logical operations :
o And, Or, Not,…
etc.
• Operates and stores results in general
registers
• Stores operation status in flag/status
registers
 Carry occurrence, overflow occurrence

CPU Structure
FPU ( Floating-Point Unit):
• The FPU performs arithmetic operations on floating point numbers.
• An FPU is complicated to design, although the IEEE 754 standard
helps to answer some of the specific questions about implementation
• 8086 : First computer to implement IEEE FP
• Three types of the Floating-Point Data :
 The half-precision floating-point format (16-bit data)
 The single-precision floating-point format (32-bit data)
 The double-precision floating-point format (64-bit data)

CPU Structure
IEEE Floating Point Standard 754 (FPS)
1. Half precision :
 16-bits
– 10-bit mantissa
– 5-bit exponent
– 1-bit sign
2. Single precision :
 32-bits
– 23-bit mantissa
– 8-bit exponent
– 1-bit sign
3. Double precision :
 64-bits
– 52-bit mantissa
– 11-bit exponent
– 1-bit sign
31 30 23 22 0
S Exponent Mantissa (bits 0-22)
63 62 52 51 0
15 14 10 9 0

Pipeline :
• Continuous and parallel streaming of instruction to the CPU.
• A method of achieving higher execution speed at same clock
speed.

Instruction set architecture (ISA)
 The computer ISA defines all of the programmer-visible
components and operations of the computer
 memory organization

address space -- how may locations can be addressed?

addressability -- how many bits per location?
 register set

how many? what size? how are they used?
 instruction set

opcodes

data types

addressing modes
 ISA provides all information needed for someone that
wants to write a program in machine language (or translate
from a high-level language to machine language).

CISC & RISC
CISC RISC
Complex Instruction Set Computer Reduced Instruction set Computer
More no of instructions Less no of instructions
Programming is easy Programming is difficult
8085,8086,Pentium PIC,AVR, ARM
Any instructions may refer memory Only LOAD/STORE refer memory
Not pipelined or less pipelined Highly pipelined
Small code sizes large code sizes
Instructions generally take more than 1
clock to execute.
Instructions execute in one clock
cycle.
Complex in Design Simple in Design

Memory Unit:
• Memory is a part of the Any Computer System used for data storage.
• Types of Memory :
 Volatile Memory .
 Non Volatile Memory .

Memory Unit:
Volatile memory :
RAM memory (Random Access Memory) :
• Refers to the ability to access any memory cell directly. RAM is much
faster than ROM . It used to write and read data values while program
running .
• Volatile : if you remove the power supply its contents are lost.
• Any variable used in a program is allocated into RAM.
• local variables, pointers, functions, recursive functions results
in using large amounts of RAM
• Types Of RAM :
 Dynamic RAM (DRAM)
 Static RAM (SRAM)

Memory Unit:
Static RAM Dynamic RAM

Static RAM (SRAM) Dynamic RAM (DRAM)
Made From flip-flops. Made From capacitors
High cost (per bit) Low cost (per bit)
High using power Low using power
Fast Slow
Used in cache Memory Used in main memory
Large In size Low in Size
Will retain state forever Automatically discharges after
sometime, need refreshing

Memory Unit:
Cache Memory
Small amount of memory that is faster than RAM
Slower than registers
Built using SRAM
Range from few KB to few MB
Use by CPU to store frequently used instructions & data
Spatial & temporal locality
Use multiple levels of cache
L1 Cache – Very fast, usually within CPU itself
L2 Cache – Slower than L1, but faster than RAM
Today there’s even L3 Cache

Memory Unit:
Cache Read
Operations

Memory Unit:
Caching in Multi-Core
Systems

Memory Unit:
Caching in Multi-Core Systems
(Cont.)

Memory Unit:
Core i7 Die & Major
Components

Memory Unit:
Non-Volatile memory :
• ROM(Read Only Memory):
 Permanent memory(Non-Volatile memory).
 Used as Program Memory in Micro-Controller.
 ROM generally slower than RAM.
 The size of program that can be written depends on
 Written upon programming the microcontroller.
 Can't be written/modified at run time.
• ROM Types:
 Masked ROM .
 OTP ROM .
 UV EPROM .
 EEPROM .
 Flash EEPROM .

Memory Unit:
1-Masked ROM (MPROM) :
-Programmed by the manufacturer.
-The term ‘masked’comes from the manufacturing
process.
-In case of a large-scale production, the price is
very low.

Memory Unit:
2-OTP (One Time Programmable):
- Also called programmable ROM(PROM).
- Enables programmer to download a program into it one time only.
- Used when the firmware is stable and the product is shipping in
bulk to customers.
- If an error is detected after downloading, the only thing you can do is to
download the correct program to another chip.

Memory Unit:
3- UV EPROM (UV Erasable Programmable ROM)
- It enables data to be erased under strong ultraviolet light
- After a few minutes it is possible to download a new pro
gram
- the package of this microcontroller has recognizable“”wi
ndow””on the upper side. It enables surface of the silicon
chip to be lit by an UV lamp, which has as a result that
complete program cleared and a new program download
enabled

Memory Unit:
4-EEPROM(Electrically Erasable Programmable ROM)
- Can be erased by exposing it to an electrical charge.
- The contents of this memory may be changed during run
time (similar to RAM),but remains permanently saved
even if the power supply is off (similar to ROM)
- EEPROM is often used to read and store values , created
during operation, which must be permanently saved.
- Acts as peripheral of microcontroller.
- Take more time in read/write access than RAM
- The max number to Write/Erase Cycles is usually100,000
but in Read is infinity

Memory Unit:
5-Flash EEPROM
- Invented in the 80s in the laboratories of Intel.
- Represented as the successor to the EEPROM.
- Flash is normally organized as sectors (256B - 16KB).
- Large blocks of memory erased at once, rather than one
word at a time like EEPROM , So FLASH is much faster th
an EEPROM . Take more time in read/write access than
RAM
- The max number to Write/Erase Cycles is usually10,000
but in Read is infinity

Memory Unit:
Type Volatile
?
Writeable
?
Erase size Max Erase
cycles
Cost per
bit
speed
SRAM Yes Yes Byte unlimited Expensive Fast
DRAM Yes Yes Byte unlimited Moderate Moderate
Masked ROM No NO -- -- Inexpensi
ve
Fast
PROM No Once -- -- Moderate Fast
EPROM No Yes Entire chip Limited(consult
datasheet(
Moderate Fast
EEPROM No Yes byte Limited(consult
datasheet(
Expensive Fast to read
slow to write
FLASH No Yes sector Limited(consult
datasheet)
Moderate Fast to read
slow to write

Microcontrollers Selection Criteria:

Microcontrollers Selection Criteria:
AVR(Atmel) 8051(Intel) PIC(Microchip) HC11(Motorola)
Architecture Harvard Von-Neumann Harvard Von Neumann
Instruction Type RISC CISC RISC CISC
Max speed 20MHz 24MHz 20MHz 8MHz
Cycle/Instruction 1 12 4 8
Instruction/second 20MIPS 2MIPS 5MIPS 1MIPS
N of Instructions 132 215 32 200
Max program size 256KB 32KB 64KB 32KB
Data bus Width 16-bit 8-bit 14-bit 8-bit

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