Introduction to embedded systems powerpoint

The Future
 Embedded System
 Future of 21st Century
 Success in computing platforms
 Cellular phones
 PDAs
 iPOD
 iPhone
 iPAD
 Gizmos to displacement of PC and laptops
 Shaping up landscape of mobile app and mobile web
 Enabling Technologies
 Network
 Computing Platform
 Evolution of both hardware and software layers

History of Embedded Systems
• 1970
– Computers for commercial and admin apps
– Microprocessor – miniaturization – Moore’s Law
• 1980
– Computer networks – bridge IT + Telecommunication
– Mouse, Windows and GUI
• 1990
– Internet and WWW – access to digital technologies
• 2000
– Second revolution for embedded systems
• Economic Challenges
– Increase fuel economy and reduce emissions in automobile by adjusting
motor state
– Airbags and assisted braking systems – improve comfort and security of
passengers
– Improve security, performance, attractiveness and market share

Introduction to Embedded System
• System
– Way of working, organizing, performing one or many tasks as per rules or
plan
– Arrangement – units assemble and work together as per program or plan
• Examples of system
– Time display system – watch
– Automatic cloth washing system – washing m/c
• Embedded Systems are
– Omnipresent (homes, office, shopping malls, hospitals, cars, aircraft…)
– Computing Device – does a specific focused job

What is Embedded System?
 Embedded System
 any device that includes a computer but is not itself a general purpose
computer
 h/w and s/w - part of some larger systems and expected to function without
human intervention
 respond, monitor, control external environment using sensors and actuators
 embedding a computer - but not for general purpose
 Applied Computer System
 Includes analog interface to the external world

Embedded System - Definitions
• An embedded system is an application that contains at least one programmable
computer (typically in the form of a microcontroller, a microprocessor or digital
signal processor chip)
– is used by individuals who are, in the main, unaware that the system is
computer-based
» From Embedded C Programming perspective by Michael.J.Pont
• “An embedded system is a system that has software embedded into computer-
hardware, which makes a system dedicated for an application (s) or specific part
of an application or product or part of a larger system.”
– s/w usually embeds into a ROM or flash
– Independent system or part of a large system
» by Raj Kamal

Embedded System - Definitions
• “An embedded system is one that has a dedicated purpose software embedded in a
computer hardware.”
» By Raj Kamal
• Any device that includes programmable computer but not self intend to be a general
purpose computer
» Wayne Wolf
• Electronic system contains microcontroller or microprocessor but not general purpose
computers
• computer is hidden or embedded in the system
» Todd D. Morton
• Combination of Software and Hardware in which the software controls the entire
hardware for a dedicated application
» Raj Kamal
• A general-purpose definition of embedded systems is that they are devices used to
control, monitor or assist the operation of equipment, machinery or plant. “Embedded”
reflects the fact that they are an integral part of the system. In many cases, their
“embeddedness” may be such that their presence is far from obvious to the casual
observer.
>> Institute of Electrical Engineers (IEE)

Embedded System Vs Desktop System
• Desktop / Laptop
– General purpose computer
– Used for playing games, word processing, accounting, SDT etc.,
• Embedded System
– Single Purpose and
– fixed embedded software for specific job
• Typical Examples
– A/C, VCD/DVD Player, Printer, Fax m/c, Mobile phone etc
– Customized embedded hw + fixed embedded sw (firmware) + specific
processor
• to meet the specific requirement

Examples
 PDA
 Digital camera
 Cell phone
 Simple Control: front panel of microwave owen – less functionality
 Camera - Canon EOS has 3 microprocessors - 32b RISC CPU runs auto focus
 Analog TV - tuning and channel selection - less functionality
 Digital TV
 decompression, descrambling etc., more functionality
 complex signaling functions

Examples
 Automobile ES
 high end automobile may have 100 microprocessors
4b up checks tension of the seat belt
uc run dashboard devices - display services
16/32b up controls engine - most complex function
 Example Automobile system
 ABS (Anti-Lock Braking System)
 4 sensors senses the speed of wheels
 4 brakes controlled by hydraulic pump
 Embedded ABS
 receives inputs from sensors
 actuates hydraulic pump
 Similar control system implemented through microcontroller in AU

Characteristics of Embedded System
 sophisticated functionality - differ by appliances
 RT operation (not always necessary)
 low manufacturing cost
 application dependent processor and not GPP
 Restricted memory
 low power
 critical in battery operated devices
 excessive power consumption increases system cost even in wall powered
devices

 Manufacturing cost
 Non-Recurring Engineering cost (NRE) – cost for design and development
 cost of production and marketing each unit
 production cost should be taken care when targeting mass market
 Ex: AU Versus low cost cell phone
 Technology choice depends on no of units plan to produce

 RT operation
 finish operations by deadlines
 HRTS - missing deadline is catastrophic
 automated missile launch system
 SRTS - missing deadline degrades performance
 playing video - missed decoded frame
 many systems are multi rate - inputs from external world comes at different rates

 Application dependent requirements
 Fault Tolerance and Reliability
continue operation despite hw or sw faults
Ex: aircraft and medical monitoring sys
 Safe
avoid physical or economic damage to person or property

 More Features – Dedicated Systems
 Pre-defined functionalities – h/s accordingly designed
 Programmability rarely used during life time of system
not programmed on regular basis
OTP and execute infinitely
do specific task
RT, fault-tolerant and safe

• Single Functional - cannot be programmed to do different things
– pagers and mobile phones
• Limited Resources - fixed RAM, ROM
– No secondary storage CD-ROM, FDD
• Work against deadlines - Real Time systems
• Missing deadline cause catastrophe
• Power constrained - Battery powered products
• Highly reliable - No 3 finger salute – cannot afford to reset
• Extreme environment conditions - Temperature and humidity
• Cost sensitive to CE - Millions of units sold
• Diversified processors and OS unlike desktop (intel + MS - Wintel)
– complex to chose right platform

Constraints in Embedded Systems
Tightly constrained than traditional software systems
• Cost
– Cannot have high end or fast processor
– Cannot have more memory – processor footprint should be less
• Size
– Processor footprint should be less
• Ex: gun stabilization control for Arjuna Tank in Defence
• Cooling requirements + Processor should take less space
• Performance
– Ex: Digital camera snaps, Mobile phone address book contact list etc.,
• Power
– Battery power products – Mobile phones
– Optimized power saving algorithms and operating modes – reduce power dissipation
– SW Program size + # of instructions – affect processor’s energy consumption
• Available System Memory and Processor Speed
• Limited power dissipation when running system continuously
• Reactive and Real Time – Adaptive cruise control and radar missile detection systems

More Examples
 NASA Mars Rover uses an Intel 80C85 8-bit microprocessor

More Examples
 Palm Vx Handheld uses Motorolla Dragonball EZ 32-b microprocessor

More Examples
 Philips sonicare plus toothbrush – Zilog Z8 8b microprocessor

More Examples
 Vendo V-MAX 720 vending machine uses the Motorola M68HC11 8b
microprocessor
 electronic and mechanical parts should go in hand
 delivering a good wrt cash - transformed - web enabled cashless delivery
stock monitored remotely
transactions through credit or smart card
security monitor from remote

More Examples
 Sony’s Aibo Robotic Dog uses ERS-110 an MIPS 64b RISC processor
 coordinate the motions
 needs to do sensing
 control the manipulators
 need to communicate
Ex: football competition b/w robo

More Examples
 Rio MP3 Player uses 32b RISC processor
 compressed form of audio is mp3
 sophisticated up to be used for audio processing

More Examples
 Garmin Streetpiolot GPS receiver uses a 16b processor
 any transport system can get its global location
 automated navigation system make use GPS
 communication with satellite and output about vehicle position and map
display

More Examples
 Miele dishwashers uses 8b Motorola 68HC05 processors and can be
reprogrammed with a laptop to adjust temperatures and cycle times

More Examples
 Hunter 44550 programmable thermostat uses a 4b processor

Types of Embedded System
 similar to general computing
 PDA, video games, STP box, ATM
Since the functionalities is subset of PC functionalities
i/0 based
no sensing of ext environment and no control of actuators
more like general purpose
respond to users input
 Control systems
 sensing and actuating - is a specific job
 feed back control of RT systems
vehicle engines - fuel injection control
flight control
nuclear reactors

Types of Embedded System
 signal processing
 core job is processing of signals
radar
sonar
DVD players
 communication and networking
 cellular phones,
 internet appliances
 web enabled vending m/c

Nature of System Functions
 Functions expected from Embedded Systems – To do
 obey control laws - for sensing and actuation
 sequencing logic - task specific and not general
 signal processing - if there is external interface
may not be a core activity
but required to deal with sensing inputs
 app specific interfacing
what kind of sensors and actuators interconnected
h/s interfacing for i/o devices
 fault response
what happens if fault occurs
General philosophy is - graceful degradation
Catastrophic failure should not happen
Ex: battery low in mobile phone – message to user before shut down

Embedded System Architecture
 Memory - has the software to control the system
 AD conversion blocks - interface to sensors
 DA conversion blocks - interface to actuators
 integral and essential component of embedded control systems

Embedded System Architecture
 FPGA / ASIC
 special hw interfaces with CPU
 CPU off shores special functionalities
 human interface with CPU - LCD, LED
 diagnostic tools
 trace failures
 system does self checks to check all paths on regular basis using diagnostic
tools
 if not system may damage the users due to unexpected malfunctions
 power cooling systems
 proper package of whole systems wrt external environment
 good well system can fail due to improper packaging
 Ex: moisture controlling
 mechanical aspects of design - too critical

Implementing Embedded System
 HW
 PE - uc and up
 peripheral devices
i/o
interfacing sensors and actuators
interfacing protocols
 Memory
 Bus
 HW aspects looks similar to general purpose systems
 But embedded systems differ by peripherals
General purpose is about std i/o devices
in ES - i/o devices varies a large
 diff kinds of sensors - so PE should be defined wrt i/o devices

 cross assemblers and compilers
 host and target m/c
 Ex: compiler for PIC uc on simple PC
compile c program for PIC uc (target board)
not executed on PC in which it is compiled
 compilers for family of processors (variants)
since similar architecture but differ by registers or features
 emulators
 IS emulators
 emulates target processor on another m/c
 simulation environment
 timing analysis of code on host m/c

 PC - hw connector - target board
 monitor execution of code from PC
 debugging tools
 System SW
 Cross compilers and assemblers
 emulators and simulators
 debugging tools
 System SW aspects differ from that of general purpose system
 Top of the system sw is specialized OS with RT features if required
 App sw - flavors for different devices
 Ex: same os vxworks on laser printer and on other appliances
 app sw targeted for printing on top of OS
 app sw distinguish the functionality

History of HW Evolution
 Based on faster clock and degree of integration
 GP up and uc
get OTS products and develop system out of it
Development cost (NRE) is reduced by using GP up and uc
 DSP
signal processing is the basic task
cost is more than GP
 AS processors (ASSP / ASIC)
designing processor that exactly suit application need
development cost is more
application will be an additional cost
 SoC
multi cores + Co-Processor + peripherals
Ex: TI - RISC + TI DSP + entire communication integrated
more sophisticated functionalities

History of Processor Architecture Evolution
 Von-Neumann Architecture
 Primitive architecture
 Computer programs – small and simple but memory is costly
 Program and data stored in same memory
 Instruction and data access on same bus from memory
 Single bus b/w CPU and memory
 RAM and program memory share the same bus and same memory and so must
have same bit width
 Each instruction fetched from memory, decoded and executed
 On decoding, any operands required fetched from same memory
 Bottleneck: getting instructions interfere with accessing RAM
 Provide address on bus to fetch instruction as well as data
 Use bus to r/w data onto memory
 No diff b/w data and instruction
 Distinct cycles for getting address and data
 Stored program computers
 Instructions / programs stored in ROM
 No changes at run time

 Harvard Architecture
 Separate data paths (address and data buses) – access code (program) and data (data
operands) - Separate program and data bus – buses can be of different widths
 Next instruction can be fetched while decoding and executing current instruction =>
Instruction pipelining is easy
 Ex: program memory <- 12/14/16b bus -> cpu <-8b bus-> data
memory
 program memory different from data memory
 two distinct buses b/w CPU and memories
 Advantages
 fetch instruction from program memory - process data and store processed data
into data memory
 fetch next instruction while storing the previous result due to separate memories
and separate buses
 facilitates instruction pipelining
 fetch instruction and fetch/store data at the same time on different buses
 many uc built on harvard architecture

 Harvard Architecture Derivatives
 Modified harvard or super harvard architectures
 Multiple data paths for data access
 More suited for data intensive applications : DSP – require multiple data
operands for each instruction execution
 Fetch data operands in parallel using multiple data paths – significantly
improves performance

 CISC – Complex Instruction Set Computer – Intel 8086, Pentium
 Earlier application were in machine or assembly code – no HL / MLL
 Computer hw supported large instructions – simplify programming – easier and
faster
 Instructions do complex operations
 Single instruction fetch multiple operands and execute multiple operations on the
operands
 Advantages
 Made programming easier – less instructions to do given task
 Favored for low memory – memory cost is reduced since less instructions to
store
 Dense instruction set to reduce memory requirements
 CISC – Basic philosophy
 Different instructions of different formats, lengths, addressing modes
 Require multiple clock cycles for execution
 More complex instructions be implemented as part of hw
 more elaborated accessing of data as part of instructions
 diff addressing modes of accessing data

 RISC – Reduced Instruction Set Computer
 CISC complex instructions take many osc cycles to execute
 Pipelined processor overall speed depends on the slowest operation being
performed
Relatively complex instructions even slow down the execution of
simpler instructions
complex instructions were a major performance bottle-neck
 Advent of compilers and HLL / MLL
 Compiler translates HLL code to low level assembly or machine code
 Compilers generally used a combination of simple instructions to achieve the
complex operations
 breaking the complex operations in to a combination of simple operations
was much efficient
took less processor cycles to execute, than doing the same operations
using a single complex CISC instruction
most of the complex instructions were not being used by compiler
generated programs

 Most of the addressing modes (offered by CISC) were also not being used by
compilers.
 This led to a shift in processor design philosophy
 Processor designers started focusing on
 reducing the size and
 complexity of instruction sets
since most complex instructions were not being used and
making a small and simple instruction set - which could be used by
compilers
 Advantages
 simpler instructions could speed up the pipe-line and thus provide a
performance improvement.
 simple instruction set implies less computer hardware and thus reduced cost.

 RISC basic design goals
 Less # of instructions – instruction designed for simple operations executed
in single cycle
 provide basic simple instructions, which could execute faster.
 Compilers could use these instructions to construct complex operations
 Each instruction is of fixed length
facilitates instruction pipelining - reading of next instruction byte will
not interfere current instruction being read
Design fetch cycles to fetch words of fixed length corresponds to
single instruction
 large # of general purpose register set
contain data or address (symmetry) - used for address and data
manipulation equally

 Load / Store Architecture of RISC
 ALU operations always involve registers and not memory locations
no memory access for data processing instructions
 load instructions to load data from memory to register
 store instructions to store processed data from register to memory
 RISC Architecture => referred to as Load/Store Architecture
 Implementing pipelining in CISC architecture is more complex than RISC arch
 Interesting trend in this era (early eighties)
 sharp increase in the speed of processors (whereas the memory speeds still
remained comparatively low)
This meant that memory accesses were becoming a bottle-neck.
This led to the design of processors with large number of internal
registers
used for temporary storage rather than depending on external and
slower memory and cache memories.

 DSP
 special purpose processors
 processing units and instruction set suit the Signal Processing Applications
 MAC (Multiply and Accumulate) and Shifter (Arithmetic and Logical shift) units are
added to the DSP cores
 Signal Processing Algorithms heavily depend on such operations
 Other common features in DSP architectures
 Circular Buffers, Bit Reversal Addressing, Hardware Loops, and DAG (Digital
Address Generators)
 Signal Processing Applications are data intensive
 the data I/O bandwidth of DSP processors is designed to be high
 lot of embedded systems run signal processing applications (cell phones, portable
media players etc)

 VLIW Architecture
 “Very Large Instruction Word” architecture consists of multiple ALUs in parallel
 designed to exploit the “Instruction Level Parallelism” in application.
 Programmers can break their code such that each ALU can be loaded in parallel.
 The operation to be done on each ALU (in a given cycle) forms the instruction
word (for that cycle).
 It is completely up to the programmer to take care of partitioning of the application
across different ALUs.
 Also, it is programmer’s burden (and compiler’s burden if the code is being
written in high level language) to make sure that there is not interdependency
between the instructions with are part of “instruction word”.
 The processor does not have any hardware to ascertain (and reschedule) the order of
instructions (this is called static scheduling).

Characteristics of Embedded SW
 logically and temporally correct programs
 cant do correct at wrong time
 correct operation has no meaning
 deal with inherent physical concurrency
 GP m/c - multi users and processes running
 ES - physical world is concurrent - have to support concurrency
Reactive Systems
 has to be reliability and fault tolerance
 has to be app specific and single purpose

Multitasking and Concurrency
 deal with several i/o and multiple events occurring independently
 Many of ES - expected to be multitasking
 separating tasks simplifies programming complexity
 but requires s/w mechanism for multi-tasking - switching b/w different tasks
 concurrency => appearance of simultaneous execution of many tasks

Challenges in ES Design
 how much hw do we need?
 word size of CPU and size of memory
 how do we meet our deadlines (deadlines for a RT system)
 faster hw or cleverer sw
 faster cpu means extra cost
 cleverer sw requires faster cpu
 so, design logic on FPGA or ASIC a dedicated function using low cost cpu and
include it for compromising on cost
 dedicated logic on FPGA or ASIC to compromise of SW so as to meet deadline
 how do we minimize power
 turn off unnecessary logic
 reduce memory accesses

ES Design – A Global Picture
 multi objective
 dependability
not fail
should have fault tolerance or graceful degradation
 affordability
depending on the market targeted
 safety
 security
not cause bodily harms to users
 scalability
 timeliness
operation in time

ES Design – A Global Picture
 To meet above multi objectives of ES design we need multi-discipline
electronic hw
mechanical hw
control algorithms
sw
humans
society / institutions
sociological acceptance of product - accept by society

ES Design – Life Cycle
 ES Design Life cycle events
 LC => how do a ES gets developed
Requirements
Design
Manufacturing
Deployment
Logistics of maintaining the system
Retirement support

ES Design Goals
 performance
 overall speed, deadlines
 funtionality and user interface
 mfg cost
 power consumption
 phy size etc.,
 size and power also related to performance and should be taken care accordingly
 Ex: cannot design a digital camera of wt 10 kg

ES Design Goals
 Functional and Non Functional Requirements part of ES design
 Functional requirements
 o/p as a function of i/p - specification of ES as i/o
 Non Functional requirements
 time to compute o/p
 size
 weight
 power consumption
 Reliability etc.,
 functional and non functional requirements are critical for product acceptance

Design and Development Process of ES Life Cycle
 Requirements
 Specifications
 Architecture
 Components Design
 System Integration
 Testing is critical
GP system - patch download for a bug
ES system - use forever and no flexibility for patch update

ES Design Approach
 TD or bottom up as like SDLC
 TD
 start from most adt description work to most detailed
 BU
 work from small components to big system
 re-use of parts already developed
 real design uses both techniques
 stepwise refinement (both h/s development go in hand)
 at each level of ADT analyze design to determine characteristics of current
state of the design
 refine design to add detail
 in ES: since special purpose h/w is designed if deadline not met with SW
 so hw and sw design should go in hand

Microcontroller
 Device
 Integrates # of components of microprocessor system on to a single microchip
 Optimized to interact with ext world through on-board interfaces
 i.e. it is a little gadget that houses a microprocessor, ROM (Read Only Memory),
RAM (Random Access Memory), I/O (Input Output functions), and various other
specialized circuits all in one package.
 Microprocessor
 Optimised to coordinate flow of information b/w separate memory and
peripheral devices located outside itself
 System bus (AB / DB / CB) - up uses to select the peripheral for sx/rx data
 Microcontroller
 Processor and peripherals on single silicon
 Self-contained device – rarely bus structures extend outside package

Microprocessor Vs Microcontroller
Microprocessor
 Collection of on/off SWI on Silicon
for computations
 CPU is stand-alone, RAM, ROM, I/O,
timer are separate
 designer can decide on the amount of
ROM, RAM and I/O ports.
 Expandable
 Expensive
 High Speed (1000 MIPS)
 General purpose and Versatile
 Large Architecture (32b, 64b)
 Lots of IO and Peripherals externally
connected
Microcontroller
 Small and self-suffice SoC to control
devices
 CPU, RAM, ROM, I/O and timer are
all on a single chip
 fix amount of on-chip ROM, RAM,
I/O ports
 Not Expandable – no external bus
interface
 for applications in which cost, power
and space are critical
 Low speed, on the order of 10 KHz –
20 MHz
 single-purpose
 Small usually an 8b
 Limited IO, enough for intended app

Microcontroller – Fundamental Components
 Microcontroller incorporates onto the same microchip the following:
 The CPU core
 Memory (both ROM and RAM)
 Some parallel digital I/O
 Microcontrollers will also combine other devices such as:
 A Timer module to allow the microcontroller to perform tasks for certain
time periods.
 A serial I/O port to allow data to flow between the microcontroller and
other devices such as a PC or another microcontroller.
 An ADC to allow the microcontroller to accept analogue input data for
processing.

Basic Microcontroller Architecture
 Memory Unit
 Store data and program
 Addressing and memory locations
 Control line to r/w
 CPU
 ALU + CU + Shifter + Memory L/S opns
 Processor Registers
 Connection b/w memory and CPU
 Bus
 Wires in power of 2 – address, control and data bus
 address bus – wires = amount of memory
 data – word length – connect all blocks inside microcontroller
 MU + CPU + BUS – self contained unit + no external interface

 External I/O Interface
 Block with several memory locations
 One end to DB and other end to output lines on uc – pins on IC
 Input-output unit
 Ports are memory locations
 Types of ports : input, output or bidirectional ports.
 Working with Port
Select the port
Configure for i/o and r/w data
 Ports simply acts like memory locations

 Serial Communication
 Parallel data transfer lines affects economy
 3 line with protocol preferred
 Ex: Serial Protocol – Non Return to Zero
 Full Duplex communication
 Data transferred serially (bit by bit)
 Rx => Data read from received port location and stored in memory
 Sx => data from memory via bus to sending port location and to rx unit as
per protocol
 Timer Unit
 Info about time duration, protocol in serial communication
 free-run counter which is in fact a register whose numeric value increments
by one in even intervals – elapsed time calculation b/w time intervals

 Watchdog Timer
 flawless functioning of the microcontroller during its run-time
 What if uc stops working or works incorrectly due to interference?
 PC => reset but ES => no reset button since no human intervention
 Watchdog Block - in fact another free-run counter
SW program needs to write a zero in every time it executes correctly.
If SW "stuck", zero will not be written in
counter alone will reset the microcontroller upon achieving its
maximum value.
This will result in executing the program again, and correctly this
time around.
an important element of every program to be reliable without man's
supervision

 Analog to Digital Converter (ADC)
 Peripheral signals (voltage) differ from uc signals (binary)
 ADC block for conversion
 Assembling all the blocks into an electronic component where uc will access
the inner blocks through the outside pins

Interrupt
 Major diff b/w DTP SW and embedded sw is ‘interrupt’
 Low level perspective
 hw mechanism for notification to CPU about event occurrence
Internal events: overflow of timer
External events: arrival of char through serial interface
 High level perspective
 Mechanism for creating
multitasking applications
 Apparently performing
>1 task at a time using a single up
 Interrupt handling in embedded
system

Why 8051?
 Price less than $1.00 (US)
1 MIPS performance
256 bytes of on-chip RAM
 Profile - price, performance, available memory match needs
 8051 architecture - by Intel
 Philips, Infineon, Atmel and Dallas
 Instruction Set / Code compatible
 60% microcontroller market - 50% of the 8-bit microcontroller market
 Used in automotive systems to children’s toys
 low cost, huge range, easy availability and widespread use of the 8051 family
makes it
an excellent platform for developing embedded systems:
ideal platform for learning about embedded systems.

Intel MCS-51 family
 Standard 40-Pin DIP pacakage
 Excellent device for building embedded systems
 Minimum # of external components to operate

Choosing a Microcontroller
 Meeting computing needs of task at hand efficiently and effectively
 Speed – highest speed supported
 Packaging – for space, assembling and prototyping of end product
 Power consumption – crucial for battery powered products
 Amount of RAM and ROM on-chip, # of Timers and IO Pins
 How easy to upgrade to high performance or low power consumption versions
 Cost per unit
 Availability of SDT (Compilers, assemblers, debuggers) and expertise
 Wide availability and reliable sources (Source of Suppliers beside Originator)
 Intel, Atmel, Philips / Signetics, Infineon, Dallas Semi / Maxim

8051 – Block Diagram
 4K bytes On-Chip ROM + 128 bytes RAM + 2 Timers
 32 I/O Pins – 4 Ports each 8b wide
 1 Serial Port + 6 Interrupt Sources
 MCS-51 Family: 8052, 8031
 8052 – 256 bytes RAM + Timer (Timer2) + 8 interrupt sources
 8031 – ROM-less 8051

Pin Description
 1-8 – Port 1 – bi-directional – individual control of pins as i/o
 9 – Reset Pin
 Logic 0 – normal run mode of chip
 Logic 1 - >= 2 machine cycles – reset chip
 10-17 – port 3 – bi-directional input port
 Dual role of individual pins
 P3.0 – RXD – receive serial data
 P3.1 – TXD – transmit serial data
 P3.2 and P3.3 – process external interrupts
 P3.4 and P3.5 – Alternative functions of T0 and T1
 P3.6 and P3.7 – r/w signals for external memory
 18-19 – external crystal, ceramic resonator or oscillator module for clock source to the
chip
 20 – Ground Vss
 21-28 – Port 2 – bi-directional input port
 Dual role - MSB address byte of 16b address to external memory
 29 – PSEN – control access to external code memory
 30 – ALE –
 When working with external memory
 Disabled to reduce EMI generated by the product
 Also used as PROG – program pulse input during flash programming
 31 – EA
 Connected to Vcc to execute code from internal memory (on chip flash)
 Connected to ground to execute code from external memory
 32-39 – Port 0 – bi-directional input port
 Does not have internal pull-up resistors
 Dual role – gives LSB address byte of 16 address to external memory
 40 – Vcc – 5V pin

Memory Issues relating to 8051
 Types of memory
 Computer tapes –access time varies for r/w wrt location on tape
 RAM – volatile r/w memories
 Same time for accessing any random memory element
 ROM – random access but non volatile
 DRAM
 r/w memory
 Capacitor along with active elements to store data
 Circuit to refresh capacitor frequently for retention
 Volatile
 SRAM
 r/w memory
 Use FF (active elements) to store information
 No refreshing
 Circuit is Costly than DRAM of same size
 Access time is 1/3 rd of DRAM

 Mask ROM
 RO from s/w developer perspective
 Manufacture able to write at the time of chip creation according to mask given by
company
 Factory programmed ROM
 Not cheap and not an option of low volume
 Mistakes are expensive
 Providing code for first mask is like character building process
 Slower access times than DRAM
 8051 members with on chip, mask programmed ROM are available
 PROM
 WORM (write once read only memory) or OTP
 PROM programmer – blow tiny fuses in the memory device
 Fuses blown cannot be repaired but devices are cheap
 Modern 8051 variants include OTP ROM

 UV EPROM
 Programmed electrically
 Has quartz window to erase memory by exposing the device to UV light
 Erasure takes several minutes
 Quartz window covered with UV opaque label after erasure
 Can withstand 1000’s of program / erase cycles
 Useful for prototyping but expensive to use in production
 More Flexible than PROM and rather primitive compared to EEPROM
 8051 members with on board UVEPROM are available
 EEPROM and Flash ROM
 More user friendly form of ROM
 Can be both Programmed and erased electrically
 EEPROM erasure is byte-by-byte basis – used to store password or persistent user data
 FLASH ROM requires block sized erase operation before programming
 Size of block in order of several KB
 Used for storage of program code
 Many 8051 members have onboard EEPROM and Flash both

Memory Organization and hex
 All data items in memory => binary codes in bits form
 Memory locations with address => simplify storage and retrieval of data items
 Byte oriented memory => each memory location has a byte with unique address
 Memory addresses in hex notation
 Hex – base-16 number system – compact way of representing large binary
numbers
 Table shows list of # with hex, ordinary and binary representations

8051 Memory Architecture
• 8051 – 128 Bytes of RAM (00H- 7FH)
• RAM memory space allocation
– 32 bytes (00H – 1FH) – register banks and stack
– 16 bytes (20H – 2FH) – bit addressable r/w
memory
– 80 bytes (30H – 7FH) – Scratch pad
• Data and parameters of 8051 programs
• Data Memory
– Store data variables and stack while program runs
– implemented using some form of RAM
– byte-oriented memory organization
– within the DATA area is a 16-byte BDATA area
which can also be accessed using bit addresses
• used to store bit-sized variables
• has machine instructions which allow bit
variables to be manipulated very efficiently
• instructions can be easily utilized from C
7FH
30H
2FH
20H
1FH
17H
10H
0FH
07H
08H
18H
00H
Register Bank
0
(Stack)
Register Bank
1
Register Bank
2
Register Bank
3
Bit-Addressable
RAM
Scratch pad RAM

8051 - CODE Memory
• 8051 – 4K bytes of on-chip ROM
• Store program code – usually in some form of ROM
• May contain read-only variables (‘constants’)
– such as filter co-efficients or data for speech playback
• DTP PC Context
– Program copied from Disk to RAM
– Executed from RAM
• Embedded System Context
– code is ‘executed in place’, from ROM
–
• Consequence of the ‘execute in place’
– most applications, may require up to 10 kbytes of CODE memory, will rarely need
much DATA memory
– Many 8051 - > 20 bytes On-Chip ROM + not >= 256 bytes of RAM
• appropriate mix for most general applications

Timers
• Atleast 2 Timers – T0 and T1 (8052 – additional Timer T2)
• 16b Timers – hold (0 -65535) values
• Incremented periodically: 8051 - every 12 osc cycles
• 8051 OSC – 12MHz => 1 million increments per second
• Used to
– measure intervals of time
• For example, we can measure the duration of a function by comparing
the duration at begin and end
– generate precise hardware delays
– generate ‘time out’ facilities - a key requirement in systems with real-time
constraints
– generate regular ‘ticks’, and drive an operating system

Interrupts
• Fundamental difference b/w DTP SW and
Embedded SW
• low-level perspective
– hardware mechanism to notify a
processor that an ‘event’ occurs
– Internal events (overflow of timers) or
– External events (arrival of char through
serial interface)
• high-level perspective
– mechanism for creating multitasking
applications
• App performing more than one
task at a time using a single
processor

8051 Interrupt Sources
• 8051/8052 – support 7 interrupt sources
– two or three timer/counter interrupts (related to Timer 0, Timer 1 and – in the
8052 – Timer 2)
– Two UART-related interrupts
• share the same interrupt vector - viewed as a single interrupt source
– Two external interrupts
– In addition, there is one further interrupt source over which the programmer
has minimal control
• The ‘power-on reset’ (POR) interrupt

Serial Interface
• 8051 - serial port compatible with RS-232 communication protocol
– transfer data b/w 8051 and desktop PC/notebook PC or similar
– Serial interface is common in embedded processors and widely used
• The serial port may be used to
– debug embedded applications, using a desktop PC
– load code into flash memory for ‘in circuit programming’ (ISP)
• when code must be updated ‘in situ’ (for example, when the product is
already installed in a vehicle, or on a production line)
– transfer data from embedded data acquisition systems to a PC, or to other
embedded processors

Timers and Counters
 crucial component of most embedded systems.
 In some cases, a timer measures elapsed time (counting processor clock
ticks)
 In others, we want to count or time external events.
 The names counter and timer can be used interchangeably when talking about
the hardware.
 The difference in terminology has more to do with how the hardware is used in a
given application.
 Both differs largely by their use and not in logic

A Simple Timer / Counter
 simple timer similar to those often included on-chip within a microcontroller
 build something similar from a couple of 74HC161 counters or a programmable logic device.
 The timer shown consists of a loadable 8-bit count register, an input clock signal, and an output
signal
 Software loads the count register with an
initial value between 0x00 and 0xFF.
 Each subsequent transition of the input
clock signal increments that value.
 When the 8-bit count overflows, the output signal is asserted.
 The output signal may thereby trigger an interrupt at the processor or set a bit that the processor can
read
 To restart the timer, software reloads the count register with the same or a different initial value.
 If a counter is an up counter, it counts up from the initial value toward 0xFF.
 A down counter counts down, toward 0x00.
 Start counter usually by setting a bit in a control register
 real counter would generally also provide a way for the processor to read the current value of the
count register at any time, over the data bus

Semi-Automatic Timers
 A timer with automatic reload capability
 will have a latch register to hold the count written by the processor
 Initial value as starting point
 When the processor writes to the latch, the count register is written as well
 When the timer later overflows,
 it first generates an output signal
 then, it automatically reloads the contents of the latch into the count register
 Since the latch still holds the value written by the processor, the counter will begin
counting again from the same initial value
 Such a timer will produce a regular output with the same accuracy as the input clock.
 This output could be used to generate
 a periodic interrupt like a real-time operating system (RTOS) timer tick,
 provide a baud rate clock to a UART, or
 drive any device that requires a regular pulse.

Semi-Automatic Timers
 Initial value as end point
 timers uses the value written by the processor as the endpoint rather than the
initial count
 In this case, the processor writes into a terminal count register that is
constantly compared with the value in the count register
 The count register is always reset to zero and counts up
 When it equals the value in the terminal count register, the output signal is
asserted
 Then the count register is reset to zero and the process repeats
 The terminal count remains the same
 Initial Value or Terminal Value
 The overall effect is the same as an overflow counter.
 A periodic signal of a pre-determined length will then be produced.

Software Configuration for Timer modes
 If a timer supports automatic reloading, it will often make this a software-
selectable feature
 To distinguish between a count that will not repeat automatically and one that
will, the hardware is said to be in one of two modes:
 one-shot or periodic
 The mode is generally controlled by a field in the timer's control register

Input Capture Timer
 has a latch connected to the timer's count register
 timer is run at a constant clock rate (usually a derivative of the processor clock )
 so count registers is constantly incrementing (or decrementing, for a down counter)
 On an external signal
 latches the value of the free-running timer into the processor-visible register and
 generates an output signal (typically an interrupt)

Input Capture Timer
 Use for:
 to measure the time between the leading edge of two pulses.
By reading the value in the latch and comparing it with a previous
reading, the software can determine how many clock cycles elapsed.
 In some cases, the timer's count register might be automatically reset just after its
value is latched
 If so, the software can directly interpret the value it reads as the number of
clock ticks elapsed
 input capture pin can usually be programmed to capture on either the rising or
falling edge of the input signal.

Bus Based Computer Systems
 Created using up, IO devices and memory components
 Up is vital components of embedded computing system
 Cannot do job without IO devices and memories
 How interconnect up and devices using cpu bus
 Similarities in bus b/w platforms required for different applications – general
useful principles from basic concepts of bus
 To Know
 Cpu bus – back bone of hw system
 Memory – important component of embedded platforms – types of memory
devices
 Varieties of IO devices types
 Basic techniques for interfacing memories and IO devices to the cpu bus
 Structure of complete platform
 Development and debugging
 System level performance analysis for bus based systems
 Alarm clock design example

The CPU Bus
 Computer system
 encompasses much more than CPU
 also includes memory and IO devices
 Bus – mechanism by which cpu communicates with memory and IO devices
 Bus
 collection of wires + also defines protocol by which cpu, memory and
devices communicate
 Major role of bus – to provide interface to the memory and IO devices
 Characteristics of memory and IO device components is important

Memory issues in Embedded Systems
 Modern microprocessors do more than just read and write a monolithic memory.
 Architectural features improve both the speed and capacity of memory systems.
 Microprocessor clock rates are increasing at a faster rate than memory speeds
memories are falling further and further behind microprocessors every
day.
 computer architects resort to caches to increase the average performance of
the memory system.
 Although memory capacity is increasing steadily, program sizes are
increasing as well, and designers may not be willing to pay for all the
memory demanded by an application

Memory – Bus – Design Factors
 Functional aspects of memory
 Bus + Protocol
 Memory + Controller
 Factors for designing memory subsystem
 Speed
 Capacity or Size (not physical size)
 Cost

Memory Classification
Based on holding data
 Hold data irrespective of power => Volatile and Non-Volatile
 Volatile => memory contents erased when the power goes off
 Non – Volatile => memory holds contents (data) even if power is not there
 Ex: Magnetic Tape
 does not require power all the time to store the data
 contents available even if power is off
 volatile still can be used as back up
Functional perspective of Memory SS
 ROM and RAM - RO and R/W
 RO
 CPU place the address and it can only send read control signal
 content of the address location is passed on data bus
 R/W
 random access
 any location in memory can be accessed at the same rate
 same rate => time to place address and get the data is going to be same for all
the locations in memory, so it can be randomly accessed
 counter part of random access is serial access => block by block or byte by byte
 so in serial access time taken to access is < n+1th block

Memory Classification
 Semiconductor based Memories
 Ex: all RAM / ROM subsystems comes under this classification
 since they make use appropriate semiconductors for storage
 Contrast to semiconductor memory is magnetic tape
 Magnetic Tapes are used solely for storage purpose
 Farther away from CPU compared to other memories
 closer to CPU is Memory and farther to CPU is Tape or any storage systems
 Based on how exactly data stored
 Static RAM
Principle: Current flow exists through some active element as long as
power exists
Fast but costly
 Dynamic RAM
Passive element along with active element
Memory controller to take care of memory retention in passive element
Slow with higher capacity and less cost

Memory Hierarchies
 Memory Hierarchy basically comes from
 Speed mismatch b/w CPU and Memory System
 Principle of Locality and focus on
 Increasing the processor utilization
 Speed - Size or Capacity - Cost are in linear relation
 Fast, Medium and Slow Memories by dividing entire address space into sections
 Fast Memory – Cache – SRAM – easy and peak access – less size
 Medium Memory – Main Memory – RAM – DRAM – medium size
 Slow Memory – storage subsystems – Tapes or HDD – CPU may not directly access
- larger size
 Ex: 1KB cache - 1GB RAM - 1TB HDD
 Ensure that CPU always access only the faster memory in order to keep the processor
utilization always up
 CPU essentially access the cache – so entire address space will not used by same kind
of memory

Cache
 SRAM – Closest – Fastest – Costlier - Less Size
 Ex: 1KB Cache
 Caches are widely used to speed up memory system performance
 Many microprocessor architectures include caches as part of their definition
 cache speeds up average memory access time when properly used
 increases the variability of memory access time
 accesses in the cache will be fast,
 while access to locations not cached will be slow
 cache is a small, fast memory that holds copies of some of the contents of main
memory
 Because the cache is fast, it provides higher-speed access for the CPU
 But since it is small, not all requests can be satisfied by the cache, forcing the
system to wait for the slower main memory

Multi Level Caches
Modern CPUs may use multiple levels of cache
A Two Level Cache System is shown
The first-level cache (commonly known as L1
cache) is closest to the CPU

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