Introduction to Embedded Systems a Practical Approach

Jul 6, 2016 Introduction to Embedded Systems - A Practical Approach
1
Introduction to Embedded Systems
A Practical Approach

2
Objective(s)
● Introduce Embedded Systems
● Understand small µ-Controllers
● Design and Implement SW for µ-Controllers

3
Prerequisite(s)
● Programming experience with any high-level
programming language

4
Note(s)
● Ask any time.
● Cell phones silent, please!
● Certificates are not for attendance.

5
References
● The slides are compilation of 3 books below. When
you see the book picture on a slide, it means it has
been taken from that book.

6
License
● Creative Common Attribution 4.0 International
License
● Universities and colleges are allowed to use it on
condition that we are informed ahead.
● Please, do not use in any commercial activity
without written permission.

7
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
Object Orientation in C
●
Meeting Real-Time
Constraints
● Creating a Small
Embedded Operating
System
● State Machine Design
● Serial Communication
● Miscellaneous Interfacing
● Case Study: Hazard and
Turning Indicators

8
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

9
Embedded System
● A computer system w/ a dedicated function.
– Part of a bigger system may be

10
Deep Embedded Systems
● Our focus in this course
● Safety or Mission
critical systems
● Reliability is a big
concern.

11
Introduction to µ-Controllers World

12
Central Processing Unit and Buses

13
General Purpose (GPR’s) and Special
Function (SFR’s)Registers
● GPR
– Inside or outside CPU
– Hold intermediate
processing results
– Fastest memory access
● SFR
– Inside or outside CPU
– Predetermined function
– Controls or states CPU
and IO behavior

14
Input/Output (IO) Ports
● Connect a µ-controller w/ external world
● Have maximum current load capacity
● Pull-up, pull-down or float

15
Interrupt
● A mean of getting CPU attention
● Polling alternative in real-time architectures
– Might not be a good one

16
Memory
● Used for data storage
● Each location has unique address.
● Can be volatile or non-volatile

17
Non-Volatile Memories
● Read Only Memory (ROM)
– Masked ROM (MROM)
– One-Time Programmable ROM (OTP ROM)
– UV Erasable Programmable ROM (UV EPROM)
– Electrical Erasable Programmable ROM (EEPROM)
● Flash
– NAND
– NOR
● Non-Volatile RAM (NV RAM)

18
Volatile Memories
●
Random Access Memory (RAM)
– Static RAM (SRAM)
●
Expensive
● Small in size
●
Internal
●
e.g. cache memory
– Dynamic RAM (DRAM)
●
Cheap
●
Large in size
● External
●
Needs refreshing
●
e.g. external memories

19
Serial Communication
● Parallel connection is ideal on shorter distances.
– several meters
● Many serial protocols
– HW controlled
– Buad rate
– Examples:
●
Inter Integrated Circuit (I2C)
● Serial Peripheral Interface (SPI)
● Universal Asynchronous Receiver/Transmitter (UART)

20
Oscillator
● Synchronizes electronics circuits
● Machine Cycle >> Oscillator Cycle
– Instructions are made of several steps.

21
Power Supply Circuit
● Brown out
– Dangerous condition when µ-controller being turned off or
power supply voltage drops to a minimum
– Can cause its out-of-control performance
– µ-controller has a built-in circuit for brown out reset as soon
as it incurs a state of emergency.
● Reset pin
– Marked as Master Clear Reset (MCLR) pin
– For external reset by applying a signal for a duration of time

22
Timer/Counter
● Timer == Internal
oscillator pulses
counter
– Measures time
● Counter == External pin
pulses counter
– Counts events

23
Watch-Dog Timer
● A timer with separate oscillator circuit
● Resets µ-controller if not refreshed before its
overflow

24
A/D Converter
● Translates analog
sensor readings into
digital values
● Accepts certain input
range
● Signal conditioning
may be needed to
interface sensor with
A/D

25
Lab 0: Development Environment
● Follow your instructor to:
– Install the development environment
– Know your development environment
– Run your first code

26
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

27
Machine Code

28
Assembly Language

29
C Language
● Mid-level language
● Very efficient
● Easy to learn
● Popular and well understood!!
● Good, well-proven compilers for 8- to 32-bits CPU’s
●
A lot of resources available online
C may not be perfect for developing
embedded systems, but it is a good
choice.

30
Programming Embedded Systems in C
Work-Flow

31
Preprocessor Directives
● Commands to the compiler processed before
compilation
● starts with ‘#’
● Examples:
– #include
– #define

32
Simple C Program

33
C Data Types

34
Variables
● Any # changing its value during program
operation.
● Stored in RAM
● Variable names
– Case sensitive
– A-Z (a-z), 0 – 9, _
– Must not start with a digit
– Must not be reserved

35
Pointers
● Hold addresses of variables

36
Constants
● Have fixed values
● Stored in program flash
● Can be:
– Integer
– Floating
– Character
– ASCII
– Enumerated

37
Constants Examples

38
Operators
● Arithmetic
● Assignment
● Increment/Decrement
● Relational

39
Operatorscont’d
● Logic
– &&, || and !
● Bitwise
– &, I, ~ and ^
● Shifting
– >> and <<
● Precedence

40
Data Types Conversion
● Auto-conversion is done @:
– Operations: different types promoted to higher priority
– Assignments: different types converts to assignee

41
Conditional Operators
● if expression ● switch expression

42
Loops
● While loop
● for loop
● do-while loop

43
Arrays
● 1 D ● 2 D

44
Functions
● Has 1 return value
● Multiple or no arguments
● May return nothing

45
Function Libraries
● Names of functions being are stored in header
files.
● Functions are sorted in libraries.
● It is necessary to specify proper header file using
#include command at the program start.
● If compiler encounters unknown function, it will
look for its declaration in the specified libraries.

46
Standard C Library
● 24 C libraries
● Comes with every compiler

47
Typical Software Architecture for PC
Computers

48
Desktop Code

49
The Super Loop
● Minimal embedded C program
● Needed as we have no OS to return to

50
Pros and Cons of Super Loop
● Pros
– Simplicity
– Minimal HW resources
– Highly portable
● Cons
– Inaccurate timing
– High power
consumption

51
Example: Central-Heating Controller

52
Task-Oriented Software Engineering
● This is a task, implemented as a C function
● OS’s and schedulers call these functions (or
“release” these tasks)
● Most of our systems will be built from “void void”
functions
● Data transfer will be carried out using global
variables

53
Embedded Code

54
Lab 1: Software Delays
– Analyze SW delays
– Refactor the code you have

55
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

56
Our Target - PIC16F887
PIC16 family is
suitable for
everything from
automotive and
aerospace systems
to TV “remotes”.

57
PIC16F887 Pins

58
RAM in PIC16F887
● RAM = GPR’s + SFR’s
● Divided into 4 banks
– 2 bits in STATUS SFR
control bank selection
– Bank selection is
handled by C compiler
– Common SFR’s have
same address in all
banks

59
Stack in PIC16F887
●
A part of RAM
●
LIFO
● 8 x 13-bit registers
●
Used in subroutine implementation
– Return address saving
●
Treated as a circular buffer and no overflow
detection mechanism
●
Not accessed by programmer

60
Interrupt System in PIC16F887

61
STATUS Register
●
IRP = Indirect Addressing Bank
Selection (0 == Bank 2, 3)
●
RP1, RP0 = Direct Addressing
Bank Selection
●
TO = Time-Out (0 == WDT
timeout)
● PD = Power Down (0 ==
After SLEEP instruction)
● Z = Zero flag
● DC = Digital
Carry/Borrow (for
nibbles)
●
C = Carry/Borrow (for
MSB)

62
OPTION_REG Register

63
Interrupt System
● IF = Interrupt Flag bit (1 == Interrupt occurred)
● IE = Interrupt Enable bit (1 == Interrupt enabled)

64
Interrupt System cont’d

65
INTCON Register
Bit Description
GIE Global Interrupt Enable
PEIE
Peripheral Interrupt
Enable
T0IE
TMR0 Overflow Interrupt
Enable
INTE
RB0/INT External
Interrupt Enable
Bit Description
RBIE
RB Port Change Interrupt
Enable
T0IF TMR0 Overflow Interrupt Flag
INTF
RB0/INT External Interrupt Flag
bit
RBIF RB Port Change Interrupt Flag

66
PIE1 Register
Bit Description
ADIE
A/D Converter Interrupt
Enable
RCIE
EUSART Receive
Interrupt Enable
TXIE
EUSART Transmit
Interrupt Enable
SSPIE
Master Synchronous
Serial Port (MSSP)
Interrupt Enable
Bit Description
CCP1IE CCP1 Interrupt Enable
TMR2IE
TMR2 to PR2 Match Interrupt
Enable
TMR1IE
TMR1 Overflow Interrupt
Enable

67
PIE2 Register
Bit Description
OSFIE
Oscillator Fail Interrupt
Enable
C2IE
Comparator C2 Interrupt
Enable
C1IE
Enable
EEIE
EEPROM Write
Operation Interrupt
Enable
Bit Description
BCLIE
Bus Collision Interrupt
Enable
ULPWUIE
Ultra Low-Power Wake-up
Interrupt Enable
CCP2IE CCP2 Interrupt Enable

68
PIR1 Register
Bit Description
ADIF
A/D Converter Interrupt
Flag
RCIF
EUSART Receive
Interrupt Flag
TXIF
EUSART Transmit
Interrupt Flag
SSPIF
Master Synchronous
Serial Port (MSSP)
Interrupt Flag
Bit Description
CCP1IF CCP1 Interrupt Flag
TMR2IF Timer2 to PR2 Interrupt Flag
TMR1IF Timer1 Overflow Interrupt Flag

69
PIR2 Register
Bit Description
OSFIF
Oscillator Fail Interrupt
Flag
C2IF
Flag
C1IF
Flag
EEIF
EE Write Operation
Interrupt Flag
Bit Description
BCLIF Bus Collision Interrupt Flag
ULPWUIF
Ultra Low-power Wake-up
Interrupt Flag
CCP2IF CCP2 Interrupt Flag

70
PCON Register
Bit Description
ULPWUE
Ultra Low-Power Wake-up
Enable
SBOREN Software BOR Enable
POR Power-on Reset Status
BOR Brown-out Reset Status

71
PCL and PCLPATH Registers

72
Addressing Modes

73
Connecting Our PIC16F887
Power Supply
Reset Signal
Clock Signal

74
Clock Signal (Heartbeat) Options
Quartz Crystal for
better stabilization
Ceramic Resonator;
cheaper but less stable

75
Clock Signal (Heartbeat) Options cont’d
RC Oscillator; cheapest and least
accurate option
External Oscillator; used to synchronize
with other µ-controllers

76
Clock Frequency and Performance
● Higher frequency == Higher performance
● Higher frequency == Higher power consumption
● Keep clock @ lowest frequency.
– Not all application require maximum frequency.
– Power consumption reduced
– Programming of peripherals is simplified @ low
frequencies.
– EMI is reduced.

77
Lab 2: Know Your µ-Controller
– Skim your µ-controller data sheet
– Read a board schematic
– Read your µ-controller header file

78
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

79
IO Ports in PIC16F887
● 5 ports (A – E) w/ 35
pins
● Common features:
– Many IO pins have
alternate functions
– Each port has its
satellite (TRISX)

80
Port A
● Controlled by TRISA and ANSEL registers
– ANSEL determine if pins are analog inputs or digital IO
● Only RA0 to RA5

81
Wake-Up Unit on RA0
● A µ-controller can wake-up itself by periodic
checking of an external signal.
– After charging capacitor, device is put into SLEEP mode.
– IO pin is configured as input and generates interrupt on
logic state change.
– Capacitor discharges causing interrupt to wake-up the
device.
● Capacitor leaks fast.
– ULPWU slows leakage.

82
Port B
● Controlled by TRISA and ANSELH registers
● Only RB0 to RB5

83
Port B Built-In Pull-Up Resistors
● Ideal for push buttons (keyboard), switches and
optocouplers
● Controlled by WPUB register (1 == PU enabled)

84
Port B Interrupts on Changing Bits
● Used for checking push buttons as they register
any button press
– No need to ‘scan’ inputs
● Controlled by IOCB register (1 == IOCB enabled)

85
Port B Special Functions
● RB0/INT
– Only ‘true’ external interrupt source
– Can react to signal raising or falling edge based on
INTEDG bit of OPTION_REG register
● RB6/RB7
– Used in ICSP
– RB6 as clock
– RB7 as data

86
Port C and Port D

87
Port E
● Controlled by TRISE and ANSEL registers
● Only RE0 to RE2
– RE3 pin is always configured as an input

88
ANSEL and ANSELH Registers

89
Switches and Push Buttons
● Mechanical devices
● Not as simple as they look
● Beware of bouncing!
– Unnoticed by humans but noticed by µ-controllers

90
De-Bouncing
● HW de-bouncing
– Cheap solution
– Expensive solution
● aka SPDT switch
● SW de-bouncing
1. Test input pin and
detects a change
2. Check one more time
after a certain delay
3. If change confirmed,
switch changed
position.

91
Relays (Electrical Switches)
● Used w/ high-power devices(motors, transformers,
heaters, bulbs …)

92
LED Diodes
● Beware of quick and slow burning!

93
LED Displays
● Several LEDs molded in same case
– Each diode is treated separately.
– Ones using low current LEDs (2mA/LED)are preferable
● 7-segments displays are most common.
● Can be common anode/cathode display

94
Multiplexing LED Displays
● To reduce pins used for
connectivity
● Only a digit at a time is
active, but they change
conditions quickly
making impression
that all digits are
simultaneously active.

95
Mapping Digits to LED Displays

96
Optocouplers

97
LCD Displays
● Can display all letters
– Every character consists
of 5×8 or 5×11 dot
matrix.
● Support automatic
message shift, cursor,
LED backlight …
● Hav 3 memories

98
LCD Display Pins

99
Display Data RAM (DDRAM)
● Stores characters to be displayed
● Up to 80 characters

100
Character Generator ROM (CGROM)
● Contains standard
character map that can
be displayed
– Each character is
assigned to a memory
location

101
Character Generator RAM (CGRAM)
● Stores user defined
characters to be displayed
● 64 bytes
– Memory registers are 8 bits
wide
– Only 5 lower bits are used
– 1 == dimmed dot
– 8 locations grouped
represent one character

102
LCD Basic Commands
● All data transferred to D0-D7 will be interpreted as
a command or a data.
– RS == 1: D0 – D7 are addresses of the characters to be
displayed.
● Character map address
● DDRAM address specifies location on which the character is to
be displayed
– Defined prior to transferring character or automatically incremented
– RS == 0: D0 – D7 are commands

103
LCD Basic Commands cont’d

104
LCD Connecting

105
LCD Initialization – Default Mode
1.Display is cleared for 15 ms.
2.Mode
– DL = 1 – Communication through 8-bit interface
– N = 0 – Messages are displayed in one line
– F = 0 – Character font 5 x 8 dots
3.Display/Cursor on/off
– D = 0 – Display off
– U = 0 – Cursor off
– B = 0 – Cursor blink off
4.Character entry
– ID = 1 Displayed addresses are automatically incremented by 1
– S = 0 Display shift off

106
LCD Initialization – 8-Bit Mode

107
LCD Initialization – 4-Bit Mode

108
Lab 3: Counting Goats
● Complete the missing code.
● Make sure it runs!

109
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

110
View on Object Oriented Code
OO languages are no readily available
for small embedded systems because
of their features overhead

111
Object Oriented C?
● Modular file based classes

112
Example: PC_IO Library – PC_IO.H

113
Example: PC_IO Library – PC_IO.C

114
Example: PC_IO Library – PC_IO.C cont’d

115
Example: PC_IO Library – PC_IO.C cont’d

116
Project Header – MAIN.H
● Groups device key information you need along
with other key parameters
– Easier to read code
– Easier to port to other devices

117
Example: MAIN.H

118
Example: MAIN.H cont’d

119
Port Header File – PORT.H
● Groups all the pin allocations to a single file for the
project
● Avoids potential conflicts

120
Lab 4: Counting Goats – Revisited
● Refactor the Counting Goats project.

121
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

122
Real-Time Systems
● RT system = Correct function @ Correct time
● RT systems are:
– Hard: missing deadlines will cause a disaster
– Firm: missing deadlines is not tolerated and will cause
malfunctioning
– Soft: missing deadline can be tolerated

123
Importance of Real-Time Systems

124
Food for Thought
● Which is more important when designing a RT
system?
– Best Case Execution Time (BCET)
– Worst Case Execution Time (WCET)
– Relation between BCET and WCET
● How can we generate accurate timing?

125
What are the Problems Below?

126
The Loop Timeout Mechanism
● Assuming 16-bit variables, the loop will run a
maximum of 65535 times before timeout
● The exact maximum time of the loop has to be
tested, but ensures that loop eventually exits.
● The timeout duration can be changed by using
different starting values for the timeout variable.

127
Hardware Timeout Mechanism
1.Initialize HW timer with an initial value
2.Start SW task
3.Check HW timer did not overflow

128
Sandwich Delays

129
A Simple Cyclic Executive

130
Sandwich Delays in Action

131
Timer TMR0
● 8-bit timer/counter with the following features:
– 8-bit prescaler (shared with Watchdog timer)
– Programmable internal or external clock source
– Interrupt on overflow
– Programmable external clock edge selection
● Controlled by OPTION_REG register

132
Timer TMR0 cont’d

133
Notes about Timer TMR0
● If prescaler assigned to TMR0, any write to the TMR0 register clear
prescaler.
●
If prescaler assigned to WDT, CLRWDT instruction clear both prescaler and
WDT.
● Write to TMR0 timer, will cause pulse counting to start after two instruction
cycles delay.
● TMR0 overflow interrupt cannot wake-up the processor from SLEEP mode.
● When used as an external clock counter, without prescaler, a minimal pulse
length or a delay between two pulses must be 2 TOSC + 20 nS.
● When used as an external clock counter with prescaler, a minimal pulse
length or interval between two pulses is only 10nS.
●
8-bit prescaler register cannot be directly read or written to.

134
Timer TMR1
●
16-bit timer/counter with the following features:
– Programmable internal or external clock source
– 3-bit prescaler (1, 2, 4 or 8)
– Optional LP oscillator
– Synchronous or asynchronous operation
– Timer TMR1 gate control (count enable) via comparator or T1G
pin
– Interrupt on overflow
– Wake-up on overflow (external clock)
– Time base for Capture/Compare function

135
Timer TMR1 cont’d

136
Notes about Timer TMR1
● Synchronization can be done in case of external clock
source only.
● Prescaler register cannot be directly read or written to.
● External clock source can wake-up device in SLEEP mode.
● Counter registers a logic one (1) on input pins. @ least one
falling edge must be registered prior to starting pulse
counting.

137
Timer TMR2
●
8-bit special timer
●
The TMR2 and PR2 registers are both fully readable
and writable.

138
T2CON Register

139
Lab 5: Counting Goats – Revisited
● Refactor the Counting Goats project to use HW
delays and timeouts.

140
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

141
Need for Accurate Timing
● Most embedded applications require tasks to be
performed periodically:
– Generating sound from stored samples
– Measuring the speed of a vehicle every 0.5 seconds
– Refreshing a display 40 times per second
– Logging vibration data from sensor at a rate of 1000 Hz
– Scanning a keypad every 200 ms
– ...

142
The Super Loop – Revisited
● This will be fine, if:
– We know the precise duration of function X()
– Period never varies

143
Basis of Small Embedded OS

144
Basis of Small Embedded OS cont’d

145
Features of Small Embedded Operating
System
● Can run tasks @ specified rates
● ISR’s are easy to manage in high-level language.
● Framework to develop embedded systems
● Puts the processor “to sleep” between tasks:
– To conserve power
– To reduce task jitter
● Easily portable to other controllers

146
Small Embedded OS Listing – Timer ISR

147
Small Embedded OS Listing – Timer
Initialization

148
Small Embedded OS Listing – Timer
Initialization cont’d

149
Small Embedded OS Listing – Power Down

150
Constraints for Small Embedded OS
● Tasks and scheduling
– sEOS can schedule a single task (function in C) to be run
periodically
● Tick interval
– Automation of tick interval is really needed
– Using “odd” frequency oscillators limits tick period
precision

151
The Super Loop – Re-factored

152
Creating Useful Tasks for Small
Embedded OS
● “Embedded C” gives a
number of examples of
tasks for use with TTC
architectures
● “Patterns for Time-
Triggered Embedded
Systems” also has
many relevant
examples

153
Example: Reading a Switch

154
C/C’s of Small Embedded OS
● sEOS == TTC scheduler
– Co-operative environment avoids overheads and
potential problems of multitasking environments.
– Workload of a TT system can be ensured to be evenly
distributed at design time: in most cases, unlike a system
in which multiple interrupts are enabled.

155
1 µ-Controller == 1 Interrupt
● In theory, for an embedded system w/ TT
architecture we mean that we can determine in
advance what it will do at every moment of time
during its execution.
● In practice, TT usually means:
– One interrupt source per CPU
– The interrupt is often (not always) a “timer tick”
– Peripherals are ‘polled’.

156
Limitations of TTC Schedulers
● As active task controls system and cannot be
interrupted by scheduler, a task overrunning its
allotted time can cause problems.
● Its by design to ensure (WCET) of any task is less
that the tick interval.

157
Limitations of TTC Schedulers
● All code ends up in one
ISR.
● Hard to maintain
● Minimal separation
between OS and task
set

158
A Better TTC Scheduler
● Builds on sEOS
● Supports execution of multiple periodic tasks with
different periods and different initial delays
● Moves user tasks out of the Timer ISR
– Greater task independence (easier to re-use / recycle)
– Can detect if a task overruns
● Still easy to understand with limited resources

159
TTC Functions and Data Structures
● Task array
● Initialization function
● Start function
●
Update function
● Dispatcher function
● Sleep function
● Add task function
● Delete task function

160
Task Array

161
Initialization Function

162
Add Task Function

163
Start Function

164
Update Function

165
Dispatcher Function

166
Dispatcher Function cont’d

167
Dispatcher Function cont’d

168
Sleep Function

169
Delete Task Function

170
Using TT Cooperative Scheduler
●
Phase 1 – Initialization
1. Scheduler is initialized by the SCH_Init function.
2. Tasks are added to the task set using SCH_Add_Task
function.
3. Scheduler is started using the SCH_Start function.
●
Phase 2 – Normal operation
1. Dispatcher SCH_Dispatch_Tasks is called in a while(1) loop.
2. After running all tasks scheduled to run in a tick, the
scheduler puts the system into sleep.

171
TTC Considerations – Task Execution
Sequence
● If multiple tasks to run @ same tick, sequence is
determined by storage order in task array.
– Varying task sequence == Different algorithms
● If scheduler not overloaded, jitter for a given task
depends on:
– Scheduler overheads (small and predictable)
– Execution times of other tasks running before it in the
same tick

172
TTC Considerations – Task Execution
Time
● Ideally, sum of WCET of all tasks in a tick < tick
● However, if sum of WCET of all tasks in a tick > tick:
– Scheduler will finish running tasks in current tick in their
order before tasks in next tick.
– Scheduler will catch up if there is sufficient slack in
subsequent ticks.
– System will meet specifications if no deadlines are
missed.

173
Lab 6: Milk Pasteurization

174
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

175
Multiple States in Systems
● Most embedded systems can be modeled in terms of
their states.
– Transition between states may result in the execution of a
particular sequence of functions.
● Some examples
– Auto pilot system
– Industrial robots
– Traffic lights
– Automatic washing machine

176
Classifications of Multi-State Systems
● Time-dependent, multi-state systems
– Basic traffic light control system
● Time- and input-dependent, multi-state systems
– Washing machine
● Input-dependent, multi-state systems

177
Example: Basic Traffic Light
● Timed four-state system
1.Red (for 20 seconds)
2.Red and amber (for 5 seconds)
3.Green (for 30 seconds)
4.Amber (for 5 seconds)
● No inputs to the system

178
Example: Basic Traffic Light Listing

179
Example: Basic Traffic Light Listing cont’d

180

181

182

183

184
Lab 7: Washing Machine Controller

185
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

186
What is RS-232?
● Recommended Standard 232 first appeared in 1960s
and defines:
– Protocol to be used for data transmission
– Voltages to be used on the signal lines
– Connectors to be used to link equipment together
● Widely used at data rates up to around 115 or 330
kbits /second (k baud)
● Used to communicate with devices at 15 meters or
more

187
Is It Significant?
● Used by most of the newer µ-controllers for in
system programming (ISP) or in circuit
programming (ICP)
● Provides a link between a PC and the µ-controller
that can be used for testing, debugging and data
acquisition
● Simple, unlike USB or Bluetooth, and is still used
in some of the recent devices (e.g. GPS sensors, TV
boxes for updating the device configuration, etc.)

188
RS-232 Basics
●
Asynchronous data
transmission
●
+3V to +15V for bit value of 0
●
-3V to -15V for bit value of 1
●
Quiescent (idle) state: (1,
indefinite duration)
●
Start bit: (0, 1 x bit duration)
●
Data: (typically 7-8 data bits,
with optional parity bit)
●
Stop bit(s): (0, duration of 1, 1.5
or 2 bits)
● Defined baud rates
● HW handshaking possible

189
EUSART
● Full-duplex asynchronous transmit and receive
● Programmable 8- or 9-bit wide characters
● Address detection in 9-bit mode
● Input buffer overrun error detection
● Half-duplex communication in synchronous mode

190
EUSART Connection

191
EUSART Asynchronous Transmitter
● TXEN in TXSTA register == 1
● SYNC in TXSTA register == 0
● SPEN in RCSTA register == 1
● TX9D is used in 9-bit mode
when TX9 in TXSTA == 1

192
EUSART Asynchronous Receiver
● CREN in RCSTA register == 1
● SYNC in TXSTA register == 0
● SPEN in RCSTA register == 1
● RX9D is used in 9-bit mode
when RX9 in RCSTA == 1

193
Receiver Error Detection
● Framing error
– Indicated by FERR bit of
RCSTA register
– Does not generate
interrupt
– FERR bit cleared by
reading received data
– FERR bit canbe cleared
by clearing SPEN bit of
RCSTA register
● Overrun error
– Indicated by OERR bit of
RCSTA register
– No additional data will be
received until the OERR bit
is cleared
– Cleared by:
● Clearing CREN bit of RCSTA
register
●
Clearing the SPEN bit of
RCSTA register

194
9-Bit Mode
● TX9D must be written before writing to TXREG.
● RX9D must be read before reading RCREG.

195
Address Detection

196
TXSTA Register
Bit Description
CSRC Clock Source Select
TX9 9-bit Transmit Enable
TXEN Transmit Enable
SYNC EUSART Mode Select
Bit Description
SENDB Send Break Character
BRGH High Baud Rate Select
TRMT Transmit Shift Register Status
TX9D Ninth bit of Transmit Data

197
RCSTA Register
Bit Description
SPEN Serial Port Enable
RX9 9-bit Receive Enable
SREN Single Receive Enable
CREN
Continuous Receive
Enable
Bit Description
ADDEN Address Detect Enable
FERR Framing Error
OERR Overrun Error
RX9D Ninth bit of Receive Data

198
ESUART Baud Rate Generator
● Beside above registers, BRGH bit of TXSTA register
and BRGH16 bit of BAUDCTL register affect clock
frequency

199
EUSART Baud Rate Formula
● n == SPBRG16:SPBRG

200
BAUDCTL Register
Bit Description
ABDOVF Auto-Baud Detect Overflow
RCIDL Receive Idle Flag
SCKP
Synchronous Clock Polarity
Select
Bit Description
BRG16 16-bit Baud Rate Generator
WUE Wake-up Enable
ABDEN Auto-Baud Detect Enable

201
Master Synchronous Serial Port Module

202
SPI
● MSSP module uses 4
registers:
– SSPSTAT – status
register
– SSPCON – control
register
– SSPBUF – buffer register
– SSPSR – shift register
(not directly available)

203
I2
C

204
I2
C cont’d
● MSSP module uses 6 registers:
– SSPCON – control register
– SSPCON2 – control register2
– SSPSTAT – status register
– SSPBUF – buffer register
– SSPSR – shift register (not directly available)
– SSPADD – address register

205
SSPSTAT Register
Bit Description
SMP
Sample State in SPI or Slew
Rate in I2
C
CKE Clock Edge Select
D/A Data/Address flag in I2
C
P Stop bit in I2
C
Bit Description
S Start bit in I2
C
R/W Read/Write in I2
C
UA Update Address in 10-bit I2
C
BF Buffer Full Status

206
SSPCON Register
Bit Description
WCOL Write Collision Detect in I2
C
SSPOV Receive Overflow Indicator
SSPEN
Synchronous Serial Port
Enable
CKP Clock Polarity Select in SPI
Bit Description
SSPMx
Synchronous Serial Port Mode
Select

207
Synchronous Serial Port Mode Select

208
SSPCON2 Register
Bit Description
GCEN
General Call Enable in I2
C
Slave Mode
AKSTAT
Acknowledge Status in I2
C
Master Transmit Mode
AKDT
Acknowledge Data in I2
C
Master Receive Mode
ACKEN
Acknowledge Sequence
Enable in I2
C Master
Receive Mode
Bit Description
RCEN
Receive Enable in I2
C Master
Mode
PEN
STOP condition Enable in I2
C
Master Mode
RSEN
Repeated START Condition
Enabled in I2
C Master Mode
SEN
START Condition
Enabled/Stretch Enabled in
I2
C Master Mode

209
I2
C in Master Mode
Initialization Data Transmission Data Reception

210
MSSP Baud Rate Formula

211
Final Notes about MSSP
● In case of WCOL, SSPBUF is not written. WCOL
must be cleared by SW.
● BF is automatically cleared when SSPBUF is
consumed.
● SDA and SCL pins turn into Open Drain outputs.
– They must be connected to externally to pull-up
resistors.

212
Long TTC Task Problem

213
Example: Long TTC Task Problem

214
Example: Display Elapsed Time
● Send time elapsed since system power on over a
serial link

215
Example: Display Elapsed Time Listing

216
Listing cont’d

217
Listing cont’d

218
Listing cont’d

219
Listing cont’d

220
Listing cont’d

221
Listing cont’d

222
Listing cont’d

223
Listing cont’d

224
Listing cont’d

225
Listing cont’d

226
Lab 8: Data Acquisition

227
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

228
Capture Compare Modules
● 2 CCP module allows user to time and control
events in 3 modes:
– Capture: access TMR1 changing register
– Compare: compare TMR1 register with another register
– PWM: generate a varying duty cycle signal
● Controlled by CCP1CON register

229
CCP1 in Capture Mode
● TMR1 must operate as timer or synchronous
counter.
● It should be switched OFF before
(re-)configuration to avoid unwanted interrupts.

230
CCP1 in Compare and PWM Modes
● Compare mode
– TMR1 must be
synchronized w/ internal
clock.
● PWM mode

231
PWM C/C’s
● Period = (PR2 +1) * 4Tosc * TMR2 Prescale Value
● Pulse Width = Pulse Width =
(CCPR1L,DC1B1,DC1B0) * Tosc * TMR2 Prescale
Value
– If pulse width > period, output will be always 1.
● Resolution
– @ fixed frequency, it is the number of duty cycle
combinations we can get

232
CCP1CON Register
Bit Description
P1Mx PWM Output Configuration
DC1Bx
PWM Duty Cycle Least
Significant bits
CCP1Mx CCP1 Mode Select

233
CCP1CON Register cont’d

234

235
CCP2 Module
● True difference from CCP1 in capture mode

236
CCP2CON Register
Bit Description
DC2Bx
PWM Duty Cycle Least
Significant bits
CCP2Mx CCP2 Mode Select

237

238

239
Single Output PWM Mode
● 1 PWM signal can be
simultaneously
available on maximum
of 4 different output
pins basic or inverted.
– In inverted mode,
similar pulses are
generated in pairs: (P1A,
P1C) and(P1B, P1D).

240
Half-Bridge Mode
● PWM output on P1A, and its complementary on
P1B
– It is necessary to provide a short delay between
switching drivers on and off by using PDC0-PDC6 of
PWM1CON register.

241
Full-Bridge Mode
● All four pins are used as outputs in 2
configurations: forward and reverse

242
Full-Bridge Forward and Reverse
Configurations
● Forward
● Reverse

243
PWM1CON Register
Bit Description
PRSEN PWM Restart Enable
PDCx PWM Delay Count

244
PSTRCON Register
Bit Description
STRSYNC Steering Sync
STRx Steering Enable x

245
ECCPAS Register
Bit Description
ECCPASE
ECCP Auto-Shutdown
Event Status
ECCPASx
ECCP Auto-Shutdown
Source Select
PSSAC1,
PSSAC0
Pins P1A, P1C Shutdown
State Control
PSSBD1,
PSSBD0
Pins P1B, P1D Shutdown
State Control

246
ECCPAS Register cont’d

247
ECCPAS Register cont’d

248
A/D Converter
● 10-bit successive approximation result is stored in
ADRESL and ADRESH registers
● 14 separate analog inputs
– Pins should be configured as analog inputs by TRIS and
ANSEL (ANSELH) registers
● -ve and + ve reference voltages

249
A/D Converter cont’d
● Controlled by 4 registers:
– ADRESH - high byte of conversion
– ADRESL - low byte of conversion
– ADCON0 - control register 0
– ADCON1 - control register 1

250
A/D Converter cont’d
●
ADFM bit of ADCON1 register controls adjustment.
●
For ADC accuracy, it is necessary to provide time
delay between selecting analog input and
measurement itself.
– This time is called ‘acquisition time’ ~ 20 µs
●

251
A/D Clock Period
● TAD == time needed to complete a bit conversion
– @ least 1.6 µs
– 10-bit A/D takes around 11 TAD.
● Clock frequency and source are controlled by
ADCS1 and ADCS0 bits in ADCON0 register.

252
A/D Clock Period cont’d

253
ADCON0 Register
Bit Description
ADCSx
A/D Conversion Clock
Select
CHSx Analog Channel Select
Bit Description
GO/DONE A/D Conversion Status
ADON A/D Enable

254
ADCON1 Register
Bit Description
ADFM A/D Result Format Select
VCFGx Voltage Reference Select

255
Analog Comparators
● 2 comparators
– Inputs: RA03 – RA04
– Outputs: RA4 and RA5
● Controlled by the following registers:
– CM1CON0 is in control of comparator C1
● Work during SLEEP mode and can wake-up µ-
controller

256
Analog Comparators cont’d
● Internal Vref exists for comparators and A/D.
– 2 sources
– 2 ranges
– Can output final CVref
●
RA2
– Simple D/A!!!
● Any comparator’s output can causes interrupt.
– Checked by CMIF of PIR register
– If CMIE of PIE register and PEIE and GIE bits of INTCON register are set

257
Analog Comparators cont’d

258
CM1CON0 Register
Bit Description
CxON Comparator Cx Enable
CxOUT Comparator Cx Output
CxOE
Comparator Cx Output
Enable
CxPOL
Comparator Cx Output
Polarity Select
Bit Description
CxR
Comparator Cx Reference
Select
CxCHy
Comparator Cx Channel
Select

259
CM2CON1 Register
Bit Description
MCxOUT Mirror Copy of CxOUT
CxRSEL
Comparator Cx Reference
Select
T1GSS Timer1 Gate Source Select
C2SYNC
Comparator C2 Output
Synchronization

260
Clock Oscillator
● The oscillator mode is selected by the bits of bytes,
called Config Word, sent during programming.

261
OSCCON Register
Bit Description
IRCFx
Internal Oscillator
Frequency Select
OSTS
Oscillator Start-up Time-out
Status
Bit Description
HTS HFINTOSC Status
LTS LFINTOSC Stable
SCS System Clock Select

262
External Oscillator in EC Mode
● Up to 20 MHz
● Advantages:
– OSC2 is available as IO pin.
– No frequency stabilization
– Synchronize µ-controller w/ board electronics
– Temp external clock disabling stops device while leaving
all data intact.
● After restarting external clock, the device proceeds with
operation as if nothing has happened.

263
External Oscillator in LP, XT Or HS Modes
● Quartz crystal or ceramic resonators
– Ceramics are cheaper but less stable
● LP (low power) mode
– Drive only 32.768 kHz crystals
● XT mode
– Intermediate frequency up to 8 MHz
● HS (high speed) mode
– High frequency > 8 MHz

264
External Oscillator in RC and RCIO Modes
● Much cheaper than resonators
● RC mode
– OSC2 outputs RC frequency/4.
● RCIO mode
– OSC2 is available as IO pin.
● f = 1/T= 1/(R*C)

265
Internal Oscillator Modes
● INTOSC mode
– OSC1 is available as IO.
– OSC2 outputs RC frequency/4.
● INTOSCIO mode
– Both are available as IO pins.

266
2-Speed Clock Start-Up Mode
● For power saving if µ-controller goes to SLEEP
mode and configured in LP, XT or HS mode.
● During SLEEP, external oscillator is switched off.
● After wake-up, 1024 pulses are wasted before
execution.
● Internal oscillator is used for 1024 instead of
external one.
●
Controlled by Int-Ext Switchover option

267
Fail-Safe Clock Monitor
● Monitors external oscillator and allows µ-
controller to proceed with execution if external
oscillator fails
– Internal oscillator takes over.
● Can generate interrupt in case of failure
● External source takes over if reset successfully.
● Controlled by Fail-Safe Clock option

268
OSCTUNE Register

269
EEPROM Memory
● 256 data locations controlled by:
– EECON1 - control register
– EECON2 - control register
– EEDAT - data register
– EEADR - address register
● Take care, shared with program flash.

270
EECON1 Register
Bit Description
EEFGD
Program/Data EEPROM
Select
WRERR EEPROM Error Flag
WREN EEPROM Write Enable
Bit Description
WR Write Control
RD Read Control

271
Reading and Writing to EEPROM
● Reading
1. Write address in EEADDR.
2. Clear EEPGD.
3. Set RD.
4. Data is ready in EEDAT.
●
Writing
1. Write address in EEADDR.
2. Put data in EEDAT.
3. Clear EEPGD.
4. SET WREN.
5. Disable interrupts.
6. Write 0x55 then 0xAA to EECON2.
7. Set WR.
8. Enable interrupts.
9. Clear WREN.

272
Reset
●
Can be external or internal
●
µ-controller takes time after power before it can
operate.
– PWRT and OST internal timers monitor Treset.
– PWRT is configurable during flashing.
– PWRT resets µ-controller @ VCC = 1.2V – 1.7V.
– After 72 ms, OST resets µ-controller for 1024 quartz cycles.
– @ the end if MCLR high, µ-controller runs.

273
Reset cont’d
●
Black-out reset when
power goes off.
●
Brown-out when power
goes off slowly.
– Really dangerous
– Stored in on-chip
memory
●
Noise is special case of
brown-out.

274
Lab 9: Miscellaneous Interfacing

275
Outline
●
Introduction
●
Programming for
Embedded Systems
●
PIC16F887
●
IO Ports and Simple
Interfacing
●
●
Meeting Real-Time
Constraints
Embedded Operating
System
Turning Indicators

276
Lab 10: Car Hazard/Turning Indicators
● Using the techniques in this course to design and
implement Car Hazard Turning Indicator.
● System specs are described in the handout
requirements document.

277
● To contact us:
– www.swift-act.com
– training@swift-act.com
– (+2)0122-3600-207

Introduction to Embedded Systems a Practical Approach

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