Done by:

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Standard single-purpose processors

• Done by
• Muna Rasha
• Supervised by
• Dr. Loai tawalbeh

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Outline
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Introduction
Processors
General- purpose
Single-purpose
Custom
Standard
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Cont
General- purpose
Many computational tasks , large variety of
applications
Single-purpose
Specific computational task
Standard
Specific computational task ,wide variety of
applications
Custom
Specific computational task , particular
application
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Standard single-purpose processors

• Known as Peripherals . (exist on the periphery of
  the CPU)
• Off-the shelf ? pre-designed for a common
  task.
• Embedded system designers use standard
  single-processor rather than general-purpose
  processor to achieve the following benefits
• Fast performance
• Fewer clock cycles .
• Shorter cycles .
• Small size
• No program memory .
• Small instruction set
• Simple datapath and controller .
• Low unit cost

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Tradeoffs !!!!

• If we are already using a general-purpose
  processor, then implementing a task on an
  additional single-purpose processor rather than
  in software may add to the system size and power
  consumption.

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Timer

• A device that generates a signal pulse at
  specified time intervals .
• Mainly consist of a register, counter, and an
  extremely simple controller.
• Example how many clock cycles needed to obtain a
  duration of 3 µs from a clock cycle of 100 MHz ?
• (3x10-6 / 10x10-9 ) 300 cycles

Number of clock cycles Desired real-time value
/ Clock cycle
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How timer works?

• The register holds a count value (number of clock
  cycles).
• The counter is initially loaded with the count
  value.
• It counts down on every clock cycle .
• When zero is reached an output signal is
  generated .
• The count value is reloaded, and the process
  repeats itself.
• Note When timer is used in conjunction with a
  general-purpose processor, it is assigned it to
  an interrupt.

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Cont

• It is better to assign timer functionality to a
  special-purpose processor rather than software
  implementation, Why?!!

Because the timer functionality occupies much of
the programs run time, leaving little time for
other computations.
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Counter

• Works like timer .
• Count pulses rather clock cycles .
• Example count cars passing over a sensor

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Applications

• Reaction timer
• Time between turning light on and user pushing
  button ?!
• 16-bit timer, clk period 83.33 ns, counter
  increments every 6 cycles.
• Resolution 683.330.5 microsec.
• Range 655350.5 microseconds 32.77
  milliseconds
• Want program to count millisec., so counter will
  be 65535 1000/0.5 63535

• Cascaded counters are used to implement real-time
  clocks.

Top2
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Watchdog timer

• Inverse functionality of a regular timer.

Regular Timer
Generate a signal for us every X time units
Watchdog Timer
Generate a signal for the timer every X time units
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Cont

• Often connect this signal to the reset or
  interrupt .
• a mechanism of ensuring that our software is
  working properly .
• Failure indicating signal can be used to restart
  or test parts of the system.
• Example ATM machines .

Watchdog Timer
Failure
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UART

• Universal Asynchronous Receiver/Transmitter
• Send and receive serially but store in parallel.
• Used through long distances, or when have few
  available I/O pins.
• To reduce the expense of long communication links
  carrying several bits in parallel, data bits are
  sent sequentially.
• Start-bit, stop-bit, parity-bit.
• baud rate indicates how fast data is moving (max
  no. of symbols transferred per second). So what
  is Bit-rate ?!
• Common rates include 2400, 4800, 9600, and 19.2k.

Transmitter
Receiver
101101
101101
1 0 0 1 0 1 0 0 0 0 1 1 0 1 1
Baudrate (2s mod / 32) oscfreq / (12 (256 -
TH1)))
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Cont

• Communication may be full duplex or half
  duplex .
• UARTs are commonly used with RS-232 for embedded
  systems communications. It is useful to
  communicate between microcontrollers and also
  with PCs.
• The stop bit(1-2 bit) is the data-line's idle
  state, and provides a delay before the next
  character can start. (asynchronous start-stop
  transmission).
• Parity (odd or even)
• Odd parity is more reliable because it assures
  that there will always be at least one data
  transition .

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UART Components

• A UART mainly contains the following components
• Clock generator.
• Input and output shift registers
• Transmit/receive control
• Read/write control logic

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Special Receiver Conditions

• Overrun Error
• Occurs when the UART cannot process the byte that
  just came in before the next one arrives.
• Various UART devices have differing amounts of
  buffer space to hold received characters. The CPU
  must service the UART in order to remove
  characters from the buffer. If the CPU does not
  service the UART and the buffer becomes full,
  Overrun Error will occur.
• Framing Error
• Occurs when the designated "start" and "stop"
  bits are not valid.
• As the "start" bit is used to identify the
  beginning of an incoming character, it acts as a
  reference for the remaining bits. If the data
  line is not in the expected idle state when the
  "stop" bit is expected, a Framing Error will
  occur.

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Cont

• Parity Error
• Occurs when the number of "active" bits does not
  agree with the specified parity configuration of
  the UART
• Break Condition
• Occurs when the receiver input is in at the
  "break" level for longer than some duration of
  time. This is not necessarily an error, but
  appears to the receiver as a zero byte with a
  framing error.
• long "break" signal can be a useful way to get
  the attention of a mismatched receiver to do
  something (such as resetting itself to some
  predefined Baud).

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USART, DUART

• USART Universal Synchronous Asynchronous
  Receiver Transmitter
• Uses a clock and data line .
• No separate clock signal as in Asynchronous
  transmission .
• No start/stop bits .
• An asynchronous transmission sends nothing over
  the interconnection when the transmitting device
  has nothing to send but a synchronous interface
  must send "pad" characters to maintain
  synchronism between the receiver and transmitter
  .
• DUART Dual UART
• combines two UARTs into a single chip .
• Ex UART USART .

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Pulse Width Modulator

• PWM generates an output signal that repeatedly
  switches between high and low.

• Duty cycle the percentage of time the signal
  is high compared to the signals period .

• PWM resolution the maximum number of pulses
  that you can pack into a PWM period .

• PWM period an arbitrarily time period in which
  PWM takes place. It is chosen to give best
  results for your particular use .

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Cont
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PWM applications

• Control the average current or voltage input to a
  device .
• Ex when you have a system powered by a 5 Volt
  power supply, so if you filter a signal that has
  a 50 duty cycle you get an average voltage of
  2.5 Volts.
• LPF charges while the PWM signal is ON and
  discharges while the PWM signal is OFF
  generating an analog output.
• PWM works as DAC in cases there in no high
  resolution, speed, and cost (simple and
  cost-effective approach) .

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Cont

• Dimmer lights
• To control the brightness of the LED you have to
  control the amount of current going through the
  device.
• Quickly turn the LED on and off cause Blinking,
  that is undesired .
• Rather than changing the number of times the
  output goes on and off, we change how long the
  output stays on and off.
• The total current that flows through the LED is
  low.

• Assume active low then,
• Output is 0 most of the time and the LED will
  be ON most of the time.
• Output is Vcc most of the time which turns off
  the LED.

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Cont

• DC motor controlling
• DC motor can be controlled by a variable
  resistor, this generate heat and hence waste
  power .
• This problem is eliminated by PWM .
• Speed Is controlled by changing the pulses width
  .
• The longer the pulses, the faster the motor turns
  .
• Cost effective
• Encoding control commands in a single signal for
  use by another device
• Controlling RF car .
• For example a (1 ms) width corresponds to a turn
  left command, a (4 ms) width to turn right, and
  (8 ms) to forward .

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LCD controller

• LCD (Liquid Crystal Display)
• low-cost .
• low-power device .
• capable of displaying text and images .
• LCD types
• 7-segment LCD.
• dot-matrix LCD.
• LCDs are extremely common in embedded systems.
• LCD Controller is a simple interface between a
  processor and LCD.
• This interface is parallel bus, allowing simple
  and fast read/write.

E (Enable) clock is used to initiate the data
transfer within LCD. R/S (Set/Reset) to select
whether the data is being transferred between
the processor and the LCD.
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LCD controller instructions

• The different instructions available for use LCD
  controller are shown in the table below.

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Keypad controller

• A Keypad consist of a set of buttons that may be
  pressed to provide input to an embedded system.
• A simple keypad has buttons arranged in an
  N-column by M-row.
• When we press a button, one column output and one
  row output go high.
• To read such a keypad from software, we must scan
  the column and row outputs.

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Cont

• The scanning may instead be performed by a Keypad
  controller.
• When the controller detects a button press, it
  stores a code corresponding to that button into a
  register and sets an output high, indicating that
  button has been pressed.
• Software may poll the output every 100 ms read
  the register when the output is high .
• Instead of using polling the output can generate
  an interrupt to the general-purpose processor.

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Stepper motor controller

• A stepper motor is an electric motor rotates a
  fixed number of degrees whenever we apply a
  step signal.
• In contrast, a regular electric motor rotates
  continuously whenever power is applied, coasting
  to a stop when power is removed.
• Stepper motors obviously abound in embedded
  systems with moving parts, such as disk drivers,
  printers, photocopy and fax machines.
• A stepper motor has four coils. To rotate the
  motor one step, we pass current through one or
  two of the coils.
• Stepper motor comes with four inputs
  corresponding to the four coils.
• Rotation achieved by applying specific voltage
  sequence to coils
• Controller greatly simplifies this.

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Cont

• Single step ? 70

• Number of steps ? 140 move .

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Stepper motor controller

• stepper motor
  stepper motor controller

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Cont

• stepper motor with controller
  without controller
• The output pins on the stepper motor controller
  dont provide enough current to drive the stepper
  motor. To amplify the current a buffer is needed.

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Analog-Digital converters

• An analog-to-digital converter converts an analog
  signal to a digital signal, and a
  digital-to-analog converter does the opposite.
• Such conversion are necessary because, while
  embedded systems deal with digital values, an
  embedded systems surroundings typically involve
  many analog signals.
• We can compute the digital values from the
  analog, and vice-versa, using the following
  ratio

e/Vmax d/(2n-1)
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Cont

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DAC using successive approximation

• 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/(256-1) gt d85.
• 
  
  

½(5.63 4.69) 5.16 volts Vmax 5.16 volts.
½(Vmax Vmin) 7.5 volts Vmax 7.5 volts.
½(7.5 0) 3.75 volts Vmin 3.75 volts.
½(5.16 4.69) 4.93 volts Vmin 4.93 volts.
½(7.5 3.75) 5.63 volts Vmax 5.63 volts
½(5.16 4.93) 5.05 volts Vmax 5.05 volts.
½(5.63 3.75) 4.69 volts Vmin 4.69 volts.
½(5.05 4.93) 4.99 volts
Successive-approximation method
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Real-time clocks

• A real time clock (RTC) keeps the time and date
  in an embedded system.
• Real-time clocks are typically composed of
• Crystal-controlled oscillator .
• Numerous cascaded counters .
• Battery backup.
• RTCs are present in almost any electronic device
  needs to keep accurate time.
• The crystal-controlled oscillator generates a
  very consistent high-frequency digital pulses
  that feed the cascaded counters.
• - the first counter counts these pulses up
  to the oscillator freq., which corresponds to
  exactly one second.
• - at this point, it generate a pulse that
  feeds the next counter.
• The rechargeable back-up battery is used to keep
  the RTC running while system is powered off.
• Communication between the microcontroller and a
  RTC is accomplished through a serial bus .

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References