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Chapter 4 Standard Single Purpose Processors: Peripherals. Introduction. Single-purpose processors Performs specific computation task Custom single-purpose processors Designed by us for a unique task Standard single-purpose processors “Off-the-shelf” -- pre-designed for a common task - PowerPoint PPT Presentation
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1
Embedded Systems Design: A Unified Hardware/Software Introduction
Chapter 4 Standard Single Purpose Processors: Peripherals
2Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Introduction
• Single-purpose processors– Performs specific computation task
– Custom single-purpose processors• Designed by us for a unique task
– Standard single-purpose processors• “Off-the-shelf” -- pre-designed for a common task
• a.k.a., peripherals
• serial transmission
• analog/digital conversions
3Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Timers, counters, watchdog timers
• Timer: measures time intervals– To generate timed output events
• e.g., hold traffic light green for 10 s
– To measure input events• e.g., measure a car’s speed
• Based on counting clock pulses• E.g., let Clk period be 10 ns
• And we count 20,000 Clk pulses
• Then 200 microseconds have passed
• 16-bit counter would count up to 65,535*10 ns = 655.35 microsec., resolution = 10 ns
• Top: indicates top count reached, wrap-around
16-bit up counter
Clk Cnt
Basic timer
Top
Reset
16
4Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Timer
• Range– Maximum time interval. Equals to 2N input intervals.
• Resolution– Minimum input time interval, or the input clock period.
• Range = n * t– Where: 0 < n < 2N, t = clock period or timer resolution.
5Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Counters
• Counter: like a timer, but counts pulses on a general input signal rather than clock– e.g., count cars passing over a sensor
– Can often configure device as either a timer or counter
16-bit up counter
Clk16
Cnt_in
2x1 mux
Mode
Timer/counter
Top
Reset
Cnt
6Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Timers – Examples
• A PIC 16F84 clock runs at 4.194304 MHz, with an 8-bit timer, what frequencies can be obtained with TOP (overflow) interrupts?
• fint=f/2N
• fint=4.1943044/28
• fint=4.096 KHz
• A 16-bit counter, using auto-reload, with f=1.2 MHz is used to generate an interrupt at every 500 s. What should the reload value be?
• Tint=(2N – R)/T• 500 s = (2N – R)/f• R = (216 – 1.2*106*500*10-6)• R = 65536 – 600• R = 64936
7Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Other timer structures
Top2
Time with prescaler
16-bit up counter
Clk Prescaler
Mode
• Interval timer– Indicates when desired time
interval has passed– We set terminal count to
desired interval• Number of clock cycles
= Desired time interval / Clock period
• Cascaded counters• Prescaler
– Divides clock– Increases range, decreases
resolution
16-bit up counter
Clk16
Terminal count
=Top
Reset
Timer with a terminal count
Cnt
16-bit up counter
Clk
16-bit up counter
16
Cnt2
Top1
16/32-bit timer
Cnt1
16
8Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Input Capture Timer
• When an external signal is asserted, the timer’s values is recorded.
9Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Example: Reaction Timer
indicator light
reaction button
time: 100 msLCD
/* main.c */
#define MS_INIT 63535 void main(void){ int count_milliseconds = 0; configure timer mode set Cnt to MS_INIT
wait a random amount of time turn on indicator light start timer
while (user has not pushed reaction button){ if(Top) { stop timer set Cnt to MS_INIT start timer reset Top count_milliseconds++; } } turn light off printf(“time: %i ms“, count_milliseconds);}
• Measure time between turning light on and user pushing button– 16-bit timer, clk period is 83.33 ns, counter
increments every 6 cycles– Resolution = 6*83.33=0.5 microsec.– Range = 65535*0.5 microseconds = 32.77
milliseconds– Want program to count millisec., so initialize
counter to 65535 – 1000/0.5 = 63535
10Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Watchdog timer
scalereg
checkreg
timereg to system resetor
interrupt
osc clkprescaler
overflow overflow
/* main.c */
main(){ wait until card inserted call watchdog_reset_routine while(transaction in progress){ if(button pressed){ perform corresponding action call watchdog_reset_routine }
/* if watchdog_reset_routine not called every < 2 minutes, interrupt_service_routine is called */}
watchdog_reset_routine(){/* checkreg is set so we can load value into timereg. Zero is loaded into scalereg and 11070 is loaded into timereg */
checkreg = 1 scalereg = 0 timereg = 11070 }
void interrupt_service_routine(){ eject card reset screen}
• Must reset timer every X time unit, else timer generates a signal
• Common use: detect failure, self-reset
• Another use: timeouts– e.g., ATM machine
– 16-bit timer, 2 microsec. resolution
– timereg value = 2*(216-1)–X = 131070–X
– For 2 min., X = 120,000 microsec.
11Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
WDT
12Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
WDT
13Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
WDT
14Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Contador de RPM
• Um MCU tem 2 C/T de 16 bits, prescaler com divisões de 2, 4 ou 8, e recebem um clock estável entre 500 kHz e 8 MHz. Medir a rotação do eixo de um motor que varia entre 100 rpm e 1000 rpm. Um sensor está ligado ao eixo e produz 60 pulsos por ciclo.
– Cada rotação do motor produz entre 100 Hz e 1000 Hz• 60 cpr * 100 rpm = 6000 cpm / 60 spm = 100 cps
– Contar os pulsos do sensor em cada segundo!• Um C/T como temporizador gerando o período de 1 segundo
• Um C/T como contador de pulsos do sensor dentro de cada segundo
– Geração de períodos de 1 segundo• 1/216 = 15,259 s ou 65,536 kHz (usando o sinal overflow)
• Usando o prescaler de 8 8 * 65,536 = 524,288 kHz
15Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Serial Transmission Using UARTs
embedded device1 0
0 11 0 1
1
Sending UART
1 0 0 1 1 0 1 1
Receiving UART
1 0 0 1 1 0 1 1
start bitdata
end bit
1 0 0 1 1 0 1 1
• UART: Universal Asynchronous Receiver Transmitter– Takes parallel data and
transmits serially
– Receives serial data and converts to parallel
• Parity: extra bit for simple error checking
• Start bit, stop bit
• Baud rate– signal changes per second
– bit rate usually higher
16Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
UART Sync
17Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
I2C
18Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
I2C – PCF8574
19Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
I2C – PCF8574
20Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
SPI
• Serial Paralel Interface
21Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
SPI Timing
22Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
LED
• Must use resistor to limit current.
• Lei de Ohm:– R = V/I
• LED = diodo– VF e IF
– VF determinado pela cor
– IF determina a intensidade
• Resistor limita IF
23Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Displays
• 7 Segments
• Dot
• Dot Matrix
24Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
7-Segments
25Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
7-Segments – Multiplexed
26Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
LCD
• Nematic type
27Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
LCD
• Polarizing
28Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
LCD
• Types
29Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
LCD
• Color
30Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Pulse width modulator
clk
pwm_o
25% duty cycle – average pwm_o is 1.25V
clk
pwm_o
50% duty cycle – average pwm_o is 2.5V.
clk
pwm_o
75% duty cycle – average pwm_o is 3.75V.
• Generates pulses with specific high/low times
• Duty cycle: % time high– Square wave: 50% duty cycle
• Common use: control average voltage to electric device– Simpler than DC-DC
converter or digital-analog converter
– DC motor speed, dimmer lights
• Another use: encode commands, receiver uses timer to decode
31Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Controlling a DC motor with a PWM
void main(void){
/* controls period */ PWMP = 0xff; /* controls duty cycle */ PWM1 = 0x7f;
while(1){}; }
The PWM alone cannot drive the DC motor, a possible way to implement a driver is shown below using an MJE3055T NPN transistor.
5V
B
A
Internal Structure of PWM
clk_div
cycle_high
counter( 0 – 254)
8-bit comparator
controls how fast the counter increments counter <
cycle_high,pwm_o = 1counter >= cycle_high, pwm_o = 0
pwm_o
clk Input Voltage% of MaximumVoltage Applied
RPM of DC Motor
0 0 0
2.5 50 1840
3.75 75 6900
5.0 100 9200
Relationship between applied voltage and speed of the DC Motor
DC
MOTOR
5V
From processor
32Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
LCD controller
E
R/W
RS
DB7–DB0
LCD controller
communications bus
microcontroller8
void WriteChar(char c){
RS = 1; /* indicate data being sent */ DATA_BUS = c; /* send data to LCD */ EnableLCD(45); /* toggle the LCD with appropriate delay */}
CODES
I/D = 1 cursor moves left DL = 1 8-bit
I/D = 0 cursor moves right DL = 0 4-bit
S = 1 with display shift N = 1 2 rows
S/C =1 display shift N = 0 1 row
S/C = 0 cursor movement F = 1 5x10 dots
R/L = 1 shift to right F = 0 5x7 dots
R/L = 0 shift to left
RS R/W DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 Description
0 0 0 0 0 0 0 0 0 1 Clears all display, return cursor home
0 0 0 0 0 0 0 0 1 * Returns cursor home
0 0 0 0 0 0 0 1 I/D SSets cursor move direction and/orspecifies not to shift display
0 0 0 0 0 0 1 D C BON/OFF of all display(D), cursorON/OFF (C), and blink position (B)
0 0 0 0 0 1 S/C R/L * * Move cursor and shifts display
0 0 0 0 1 DL N F * *Sets interface data length, number ofdisplay lines, and character font
1 0 WRITE DATA Writes Data
33Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Keypad controller
N1N2N3N4
M1M2
M3M4
key_code
keypad controller
k_pressed
key_code
4
N=4, M=4
34Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
KBD
• Key bouncing
35Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Key Debouncing
• RC Network/LP Filter
36Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
• Latch
37Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
• Software– Scan column
– Scan line
– Filter closed key• Time-out
• interruption
38Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Stepper motor controller
Red AWhite A’Yellow B
Black B’
MC
3479P
1
5
4
3
2
7
8
6
16
15
14
13
12
11
10
9
Vd
A’
A
GND
Bias’/Set
Clk
O|C
Vm
B
B’
GND
Phase A’
CW’/CCW
Full’/Half Step
Sequence A B A’ B’1 + + - -2 - + + -3 - - + +4 + - - +5 + + - -
• Stepper motor: rotates fixed number of degrees when given a “step” signal– In contrast, DC motor just rotates when
power applied, coasts to stop
• Rotation achieved by applying specific voltage sequence to coils
• Controller greatly simplifies this
39Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Stepper motor with controller (driver)
2 A’ 3 A
10 7
B 15B’ 14
MC3479PStepper Motor
Driver 8051
P1.0P1.1
StepperMotor
CLK
CW’/CCW
The output pins on the stepper motor driver do not provide enough current to drive the stepper motor. To amplify the current, a buffer is needed. One possible implementation of the buffers is pictured to the left. Q1 is an MJE3055T NPN transistor and Q2 is an MJE2955T PNP transistor. A is connected to the 8051 microcontroller and B is connected to the stepper motor.
Q2
1K
1KQ1
+V
A B
void main(void){
*/turn the motor forward */ cw=0; /* set direction */ clk=0; /* pulse clock */ delay(); clk=1;
/*turn the motor backwards */ cw=1; /* set direction */ clk=0; /* pulse clock */ delay(); clk=1;
}
/* main.c */
sbit clk=P1^1;sbit cw=P1^0;
void delay(void){ int i, j; for (i=0; i<1000; i++) for ( j=0; j<50; j++) i = i + 0;}
40Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Stepper motor without controller (driver)
StepperMotor
8051
GND/ +VP2.4
P2.3P2.2P2.1P2.0
A possible way to implement the buffers is located below. The 8051 alone cannot drive the stepper motor, so several transistors were added to increase the current going to the stepper motor. Q1 are MJE3055T NPN transistors and Q3 is an MJE2955T PNP transistor. A is connected to the 8051 microcontroller and B is connected to the stepper motor.
Q2
+V
1KQ1
1K
+V
A
B
330
/*main.c*/sbit notA=P2^0;sbit isA=P2^1;sbit notB=P2^2;sbit isB=P2^3;sbit dir=P2^4;
void delay(){ int a, b; for(a=0; a<5000; a++) for(b=0; b<10000; b++) a=a+0;}
void move(int dir, int steps) {int y, z; /* clockwise movement */ if(dir == 1){ for(y=0; y<=steps; y++){ for(z=0; z<=19; z+4){ isA=lookup[z]; isB=lookup[z+1]; notA=lookup[z+2]; notB=lookup[z+3]; delay(); } } }
/* counter clockwise movement */ if(dir==0){ for(y=0; y<=step; y++){ for(z=19; z>=0; z - 4){ isA=lookup[z]; isB=lookup[z-1]; notA=lookup[z -2]; notB=lookup[z-3]; delay( ); } } }}void main( ){ int z; int lookup[20] = { 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0 }; while(1){ /*move forward, 15 degrees (2 steps) */ move(1, 2); /* move backwards, 7.5 degrees (1step)*/ move(0, 1); }}
41Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Analog-to-digital converters
proportionality
Vmax = 7.5V
0V
11111110
0000
0010
0100
0110
1000
1010
1100
0001
0011
0101
0111
1001
1011
1101
0.5V1.0V1.5V2.0V2.5V3.0V
3.5V4.0V4.5V5.0V
5.5V6.0V6.5V7.0V
analog to digital
4
3
2
1
t1 t2 t3 t4
0100 1000 0110 0101
timeanalog input (V)
Digital output
digital to analog
4
3
2
1
0100 1000 0110 0101
t1 t2 t3 t4time
analog output (V)
Digital input
42Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Given an analog input signal whose voltage should range from 0 to 15 volts, and an 8-bit digital encoding, calculate the correct encoding for 5 volts. Then trace the successive-approximation approach to find the correct encoding.
5/15 = d/(28-1)d= 85
Successive-approximation method
Digital-to-analog conversion using successive approximation
0 1 0 0 0 0 0 0
Encoding: 01010101
½(Vmax – Vmin) = 7.5 voltsVmax = 7.5 volts.
½(7.5 + 0) = 3.75 voltsVmin = 3.75 volts.
0 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0½(7.5 + 3.75) = 5.63 voltsVmax = 5.63 volts
½(5.63 + 3.75) = 4.69 voltsVmin = 4.69 volts.
0 1 0 1 0 0 0 0
½(5.63 + 4.69) = 5.16 voltsVmax = 5.16 volts.
0 1 0 1 0 0 0 0
½(5.16 + 4.69) = 4.93 voltsVmin = 4.93 volts.
0 1 0 1 0 1 0 0
½(5.16 + 4.93) = 5.05 voltsVmax = 5.05 volts.
0 1 0 1 0 1 0 0
½(5.05 + 4.93) = 4.99 volts 0 1 0 1 0 1 0 1
43Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
R2R Ladder DAC
44Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Digital-to-analog conversion
• Use resistor tree:
R
2R
4R
8R
bn
bn-1
bn-2
bn-3
Vout
45Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Flash A/D conversion
• N-bit result requires 2n comparators:
encoder
Vin
...
46Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
RAMP ADC
47Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Dual-slope conversion
• Use counter to time required to charge/discharge capacitor.
• Charging, then discharging eliminates non-linearities.
Vintimer
48Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
SAR ADC
• Algorithm1. The successive approximation Analog
to digital converter circuit typically consists of four chief subcircuits:
2. A sample and hold circuit to acquire the input voltage (Vin).
3. An analog voltage comparator that compares Vin to the output of the internal DAC and outputs the result of the comparison to the successive approximation register (SAR).
4. A successive approximation register subcircuit designed to supply an approximate digital code of Vin to the internal DAC.
5. An internal reference DAC that supplies the comparator with an analog voltage equivalent of the digital code output of the SAR for comparison with Vin.
49Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
SAR ADC
50Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Distributed-charge SAR ADC
• The DAC conversion is performed in four basic steps:
1. First, the capacitor array is completely discharged to the offset voltage of the comparator, VOS. This step provides automatic offset cancellation.
2. Next, all of the capacitors within the array are switched to the input signal, vIN. The capacitors now have a charge equal to their respective capacitance times the offset voltage minus the input voltage upon each of them.
3. In the third step, the capacitors are then switched so that this charge is applied across the comparator's input, creating a comparator input voltage equal to -vIN.
4. Finally, the actual conversion process proceeds. First, the MSB capacitor is switched to VREF, which corresponds to the full-scale range of the ADC. Due to the binary-weighting of the array the MSB capacitor forms a 1:1 divided between it and the rest of the array. Thus, the input voltage to the comparator is now -vIN plus VREF/2. Subsequently, if vIN is greater than VREF/2 then the comparator outputs a digital 1 as the MSB, otherwise it outputs a digital 0 as the MSB. Each capacitor is tested in the same manner until the comparator input voltage converges to the offset voltage, or at least as close as possible given the resolution of the DAC.
51Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
Sample-and-hold
• Required in any A/D:
converterVin
52Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
• Understanding analog to digital converter specifications, By Len Staller. Embedded Systems Design, 02/24/05.– http://www.embedded.com/showArticle.jhtml?
articleID=60403334
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