1. Embedded Systems Prepared By:- 130350111009 130350111005
Review: Introduction to Microcontrollers

2. Processors General purpose processors: Large number of pins
80386
Pentium
Core Duo
Large number of pins
External memory
External peripherals
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3. General Purpose Registers
Registers are dedicated for moving data
EAX, EBX, ECX, EDX: general purpose registers
EBP: Base pointer
ESP: Stack pointer
ESI, EDI: Index register
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4. Microcontrollers Support for peripherals inside uController
Limited number of pins
Dedicated purpose
Controlling devices, taking measurements
Controller families:
68H12: Motorola 68H11, 68HC12, …
8051: Intel 8051, 8052, 80251,…
PIC: Microchip PIC16F628, 18F452, 16F877, …
AVR: Atmel ATmega128, ATtiny28L, AT90S8515,…
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5. Rita51J 8051 128K of SRAM 128K FLASH ROM Serial port Digital I/O lines
* Figure from
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6. Motes Sensor nodes based on Atmel ATMega128 UBC 104 Embedded Systems
* Figures from CrossbowMPR-MIBUser Manual
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7. Microcontroller Families
68H12: Motorola 68H11, 68HC12, …
8051: Intel 8051, 8052, 80251,…
PIC: Microchip PIC16F628, 18F452, 16F877, …
AVR: Atmel ATmega128, ATtiny28L, AT90S8515,…
 We are going to look at 8051s
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8. Typical 8051s 32 input / output lines.
Internal data (RAM) memory bytes.
Up to 64 kbytes of ROM memory (usually flash)
Three 16-bit timers / counters
9 interrupts (2 external) with two priority levels.
Low-power Idle- and Power-down modes
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9. Datasheets – Your New Friends!
* Figure from Atmel AT89C51RD2 Datasheet
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10. Pin-Out of an 8051
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11. 8051 Components Ports RAM Interrupt Controller Timer SPI Controller
* Figure from Atmel AT89C51RD2 Datasheet
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12. 8051 Internal RAM & SFRs UBC 104 Embedded Systems
* Figure from Atmel AT89C51RD2 Datasheet
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13. Special Function Registers (SFR)
* Figure from Atmel AT89C51RD2 Datasheet
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14. Special Function Registers (SFR)
* Figure from Atmel AT89C51RD2 Datasheet
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15. * Figure from Atmel AT89C51RD2 Datasheet
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16. Ports Driving low-power peripherals ie. LEDs, relays
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17. Accessing Ports in C void main (void) {
unsigned int i; /* Delay var */
unsigned char j; /* LED var */
while (1) { /* Loop forever */
for (j=0x01; j< 0x80; j<<=1) { /* Blink LED 0, 1, 2, 3, 4, 5, 6 */
P1 = j; /* Output to LED Port */
for (i = 0; i < 10000; i++) { /* Delay for Counts */
wait (); /* call wait function */ }
for (j=0x80; j> 0x01; j>>=1) { /* Blink LED 6, 5, 4, 3, 2, 1 */
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18. Summary General information about 8051
Special Function Registers (SFRs)
Control of functionality of uController
Ports
Input/Output of uController
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19. Motivation for Next Topics
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Motivation for Next Topics

20. Tasks for Microcontroller
Controlling of processes (autonomic)
e.g. speed of vehicles, chemical processes
Control of devices through human operator
e.g. remote control, etc
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21. Example: Controller Engineering
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22. Topics for the Following Lectures
Interrupts & Timers
Communication
Analog to digital (A/D) conversation
Pulse Width Modulation
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23. UBC104 Embedded Systems
Interrupts & Timers

24. Today’s Topics
Interrupts
Timers
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25. Definition of ‘Interrupt’
Interrupts
Definition of ‘Interrupt’
Event that disrupts the normal execution of a program and causes the execution of special instructions
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26. Interrupts
Program
time t
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27. Interrupts
Interrupt
Program
time t
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28. Interrupt Service Routine
Program
Program
Interrupt Service Routine
time t
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29. Interrupt Handling
Address space in code space
Code that deals with interrupts: Interrupt Handler or Interrupt Service Routines (ISRs)
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30. Interrupt Handling
Code that deals with interrupts: Interrupt Handler or Interrupt Service Routines (ISRs)
Possible code:
void ISR(void) interrupt 1 {
++interruptcnt; }
Interrupt number
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31. Interrupts Interrupt Program time t fahr= (cent * ) +32 9 5
mov R1, cent
mul R1, 9
div R1, 5
add R1, 32
mov fahr, R1
time t
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32. Interrupt Service Routine
Program
Program
Interrupt Service Routine
mul R1, 9
mov R1, cent
mov R1, 0x90
mov sensor, R1
ret
time t
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33. Interrupt Service Routine
Program
Program
Save Context
Restore Context
Interrupt Service Routine
mul R1, 9
mov R1, cent
time t
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34. Interrupt Service Routine
Program
Program
Save Context
Restore Context
Interrupt Service Routine
mul R1, 9
mov R1, cent
eg push R1
eg pop R1
time t
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35. Interrupt Overheads Interrupt Latency Interrupt Termination
Interrupt arrives
Complete current instruction
Save essential register information
Vector to ISR
Save additional register information
Execute body of ISR
Restore other register information
Return from interrupt and restore essential
registers
Resume task
Interrupt
Latency
Interrupt
Termination
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36. Interrupt Response Time
Interrupt Latency
Interrupt Response Time= Interrupt Latency + Time in Interrupt Routine
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37. Interrupts Internal or External Handling can be enabled/disabled
Prioritized
General 8051:
3x timer interrupts,
2x external interrupts
1x serial port interrupt
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38. Interrupt Priorities
Each interrupt source has an inherent priority associated with it
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39. Interrupt Priorities Priorities can be adapted by programs
Original 8051 provides 1-bit per interrupt to set the priority
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40. 2-bit Interrupt Priorities
The 89C52RD2 provides 2bit-interrupt priorities
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41. 2-bit Interrupt Priorities (continued)
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42. 2-bit Interrupt Priorities (continued)
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43. External Interrupts Pins for external interrupts
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44. External Interrupts External Interrupts: Level- or edge-triggered
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45. External Interrupts External Interrupts: Level- or edge-triggered
Level-triggered
threshold t
trigger point
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46. External Interrupts External Interrupts: Level- or edge-triggered
Level-triggered
threshold t
trigger point
Edge-triggered t
trigger point
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47. Timer
A timer is a counter that is increased with every time an instruction is executed e.g with 12MHz increases a counter every µs
General 8051 has 3 timer:
2 16-bit timer
1 16-bit timer with extra-functionality (introduced with the 8052)
Timer/Counter Mode Control Register TMOD
Timer/Counter Control Register TCON
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48. Timer High- & Low-Registers
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49. SFR Map – Timer Registers
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50. Timer Control Timer/Counter Mode Control Register TMOD
Timer/Counter Control Register TCON
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51. SFR Map – Timer Control
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52. SFR Map – Timer 2
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53. Timer Code void TimerInit(void) {
// Timer 2 is configured as a 16-bit timer,
// which is automatically reloaded when it overflows
// This code (generic 8051/52) assumes a 12 MHz system osc.
// The Timer 2 resolution is then µs
// Reload value is FC18 (hex) = (decimal)
// Timer (16-bit) overflows when it reaches (decimal)
// Thus, with these setting, timer will overflow every 1 ms
T2CON = 0x04; // Load Timer 2 control register
TH2 = 0xFC; // Load Timer 2 high byte
RCAP2H = 0xFC; // Load Timer 2 reload capt. reg. high byte
TL2 = 0x18; // Load Timer 2 low byte
RCAP2L = 0x18; // Load Timer 2 reload capt. reg. low byte
ET2 = 1; // Enable interrupt
TR2 = 1; // Start Timer 2 running }
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54. Interrupt Code for Timer 2
void handleTimer2 (void) interrupt 5 {
/* execute interrupt code */ }
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55. Interrupt Flags Bits that are set if the interrupt occurs
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56. Code for Interrupt Flags
/* Configure Timer 0 as a 16-bit timer */
TMOD &= 0xF0; /* Clear all T0 bits (T1 left unchanged) */
TMOD |= 0x01; /* Set required T0 bits (T1 left unchanged) */
ET0 = 0; /* No interrupts */
/* Values for 50 ms delay */
TH0 = 0x3C; /* Timer 0 initial value (High Byte) */
TL0 = 0xB0; /* Timer 0 initial value (Low Byte) */
TF0 = 0; /* Clear overflow flag */
TR0 = 1; /* Start Timer 0 */
while (TF0 == 0); /* Loop until Timer 0 overflows (TF0 == 1) */
TR0 = 0; /* Stop Timer 0 */
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57. Summary: Interrupts Definition of ‘Interrupt’:
Event that disrupts the normal execution of a program and causes the execution of special instructions
Handling can be enabled/disabled
Prioritized
Internal or External
External Interrupts:
Level-triggered
Edge-triggered
8051: 3 timer interrupts, 2 external interrupts & a serial port interrupt
Level-triggered
threshold t
trigger point
Edge-triggered t
trigger point
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58. Real-Time Systems predictable Definition:
A real-time system needs to be
predictable
in terms of values and time
Correctness of an RT system depends on functionality as well as temporal behaviour
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59. Clock Driven Scheduling
Decision on what job execute are made at specific time instants chosen a priori before the system starts operation
A schedule of jobs is created off-line and used at run time
The scheduler dispatches jobs according to the stored schedule at each scheduling decision time
Clock-driven scheduling has minimal overhead during run time
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60. Cyclic Executive #define TASK_MAX 4 typedef void (func_ref)(void);
int delay[TASK_MAX];
func_ref task_ref[TASK_MAX];
void cyclic_executive() {
int task= 0;
while(1) {
settimer(delay[task]);
taskref[task]();
task= (task==TASK_MAX) ? task+1 : 0;
clear(time_flag);
while (time_flag) enterIdleMode(); }
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61. Cyclic Executive (continued)
void timer(void) interrupt 5 {
set(time_flag); }
void EnterIdleMode(void) {
PCON |= 0x01;
Frame
Tdelay,1 T1 T2 T3 T1 T2 T3 t
IdleMode
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62. Problems with Cyclic Executives
Timing Accuracy
Actually constructing the cyclic executive
(Typical realistic problem: 40 minor cycles and 400 entries)
Inflexibility
must reconstruct schedule even for minor changes
Incorporating Aperiodic/Sporadic Tasks, or very long period tasks
I/O only by polling
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63. General Embedded Programming
Endless loops
Idle mode for 8051
Generic main() function
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64. Endless Loops Two types of tasks: Run-To-Completion tasks
Endless-Loop tasks
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65. Endless Loops Two types of tasks:
Run-To-Completion tasks
Endless-Loop tasks
Interrupt handler are run-to-completion tasks
The majority of generic tasks are endless loops
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66. Endless Loops Two types of tasks:
Run-To-Completion tasks
Endless-Loop tasks
Interrupt handler are run-to-completion tasks
The majority of generic tasks are endless loops
Example Code:
void ExampleTask(void) {
while(1) {
waitForActivation;
doTask; }
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67. Idle Mode 8051s implement an “idle” mode which consumes less power
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68. Idle Mode 8051s implement an “idle” mode which consumes less power
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69. Idle Mode 8051s implement an “idle” mode which consumes less power
from Pont: Atmel 89S53
normal mode 11mA
idle mode 2mA
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70. Idle Mode void EnterIdleMode(void) { PCON |= 0x01; }
8051s implement an “idle” mode which consumes less power
from Pont: Atmel 89S53
normal mode 11mA
idle mode 2mA
Example Code:
void EnterIdleMode(void) {
PCON |= 0x01; }
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71. Generic main() Function
void main(void) {
/* initialize system */
/* initialize tasks */
while (1) { /* loop forever */
EnterIdleMode(); /* PCON |= 0x01*/ }
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72. Summary Cyclic executives Endless loops Idle mode
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