Embedded Systems (1)
• An embedded system is a computer based system which is
specifically designed to perform one or several dedicated functions
• An embedded system comprises of a combination of computer
hardware and software, perhaps additional parts, either
mechanical or electronic that are designed to perform a dedicated
• Characteristics of embedded systems
– Comprises the least required resources
– designed to execute a specific task
– often interfaced with sensors in order to get feedback of
– perform real time operations
– designed to operate under harsh environments
Embedded Systems (2)
• The central processing unit (CPU) of the embedded system is
the most important element of the system.
• The CPU is usually a processor.
• Components of a CPU
– Arithmetic logic unit (ALU) - performs arithmetic and
– Control unit (CU) – extracts instructions from memory and
decodes and executes them, calling on the ALU when
• Embedded systems are used in mobile phones, mp3 players,
video game consoles, digital cameras, DVD players & GPS
receivers use such embedded systems etc.
Microcontroller Components (1)
– Ranging from small and simple 4-bit processors to complex 32- or 64bit processors.
In-circuit programming and debugging support.
– often an oscillator for a quartz timing crystal, resonator or RC circuit.
Random-access memory (RAM)
– Type of volatile memory for data storage.
Read-only memory (ROM),
– Erasable programmable read only memory (EPROM)
– Electrically Erasable Programmable Read-Only Memory (EEPROM)
– Flash memory for program and operating parameter storage.
Microcontroller Components (2)
• Discrete input and output bits, allowing control or detection
of the logic state of an individual package pin.
• Serial input/output such as serial ports (UARTs).
– Serial Peripheral Interface (SPI)
– Controller Area Network (CAN) for system interconnect
• Peripherals such as timers, event counters.
• Pulse width modulation (PWM) generators.
• Analog-to-digital converters and digital-to-analog converters.
• This is a general purpose 8-bit microcontroller
• Developed by Microchip Technology Inc.
• Uses an 8-bit data bus which makes it possible to
access 8 bits of data in a single machine instruction
• This microcontroller has a speed of 12 MIPS.
• This microcontroller has 40 pins.
PIC18F4550 Microcontroller (2)
For the operation of the chip it requires,
1. Power at +5V using pins 11 & 32.
Ground using pins 12 & 31.
2. A precise clock input provided by a crystal oscillator with an input
frequency of 20 MHz connected to pins 13 (CLKI) and 14 (CLKO).
• This chip uses a Phase Lock Loop (PLL) frequency multiplier boost
the operating frequency of the chip to 48 MHz.
Applications of the PIC18F4550 microcontroller
Sending and receiving digital signals using the digital I/O ports
Measuring analog voltages from +0V – +5V.
Sending PWM signals for driving dc motors
Pins used for sending & receiving
Measuring analog voltages using the
• There are 5 analog input pins.
• Marked pins can measure analog
voltages between +0 V & +5 V.
• Analog voltages are measured
by using analog to digital
• The ADC has a resolution of 10bits.
analog +0 V -> digital 0
analog +5 V -> digital 1023
Generating PWM signals for
driving DC motors
• The pin 16 (C1) could be used
to send PWM signals for
driving DC motors.
• It has a digital resolution of
10-bits (0-1023 in decimal).
• The frequency of the PWM
signal is 2.44 kHz.
Microcontroller development tools: Hardware
Microcontroller development tools: Software
• IDE (Integrated Development Environment): A software
application that facilitates all aspects developing of
– Source code editor.
– A compiler.
– A debugger.
• Software interface for loading the compiled code into the