EEE237 Introduction to
Microprocessors
Week 1
Course overview
İntroduction to Microprocessor,
microcontroller and programming
basics
Course objectives
• to develop an in-depth understanding of
– the operation of microprocessors and
microcontrollers
– Assembly language programming and using C
language.
– microprocessor interfacing techniques
• to be able to use PIC16F877 microcontroller
Course objectives
• to be able to design and implement
microprocessor-based systems in both
hardware and software
• Ultimate goal: to be able to apply this
knowledge to more advanced structures
Outline
• Microcontroller
Concepts
Basics
and
Programming
• PIC microcontroller Architecture
• Programming Model, Addressing Modes and
Instruction Set
• Programming examples
• The Stack, Subroutines and Interrupts
Outline
• Timer Operations
• Analog to Digital Conversion
• Data acquisition and control examples
• Interfacing Concepts
• Parallel Input/Output
• Serial Communications
Common computer organization
(simplified view)
• ALU (Arithmetic Logic Unit) is a circuitry,
which is capable of doing various operations
(for example ADD, SHIFT, AND, OR, etc) on
certain on-chip registers.
• CPU (Central Processing Unit) is the
combination of the control logic, associated
registers and the arithmetic logic unit.
Common computer organization
(simplified view)
ALU
Input/Output
(I/O)
Memory
Control
CPU
Common computer organization (1/2)
Common computer organization (2/2)
Computer Buses
• Address bus: carries the address of a
unique memory or input/output (I/O)
device
• Data bus: carries data stored in memory
(or an I/O device) to the CPU or from
the CPU to the memory (or I/O device)
• Control bus: is a collection of control
signals that coordinate and synchronize
the whole system
Block diagram of a typical CPU
CPU Structure
• The main functions are
– data transfer
– arithmetic and logic operations
– decision making (instructional flow control)
• The register array consists of at least
one accumulator, program counter and
stack pointer
• The control unit controls all the
operations in a CPU and basically it
puts the CPU in one of the fetch and
execution phases
Memory (1/2)
• The memory in a computer system
stores the data and instructions of the
programs.
Adress
decoder
Storage
Data
bus
Area
Adress
bus
Other signals
(Vcc,Gnd,
CS, etc.)
Memory (2/2)
Main memory types
• ROM (read-only memory)
– programmed permanently at the factory,
cannot be altered
• RAM (random-access memory)
– read and write memory
• EPROM (erasable programmable ROM)
– nonvolatile, written electrically but erased
optically
• EEPROM (electrically ROM)
– nonvolatile, both written and erased
electrically
Operation of the CPU (1/2)
• Fetch cycle (phase):
– The CPU puts the address of the
instruction to be executed on the address
bus. The address info comes from the
program counter (PC) maintained by the
control unit.
– The control bus holds the info. for reading
the memory location and the data bus
holds the instruction from the memory
which is stored into the instruction register
(IR)
– PC is updated to point to the next
Operation of the CPU (2/2)
• Execute cycle (phase):
– Instruction in the IR is decoded
– The required data transfer and the required
logical and arithmetic operation are
performed
– The result is written back either to one of
the registers or memory or I/O device
• Common operations performed in ALU
are:
– addition, subtraction,
– logical AND, OR, XOR, NOT
Operation of the CPU (2/2)
Detailed Block Diagram
Microcomputer
(1/2)
• CPU on a single IC
microprocessor (µP).
• the terms CPU, µP and MPU (microprocessor
unit) are synonymous.
• CPU is the combination of the ALU and
control unit of any computer.
• When the CPU is a single IC; it is called a µP
and is also referred to as the MPU.
• When the MPU ‘s connected to memory and
I/O, the arrangement becomes a
MICROCOMPUTER.
Microcomputer (2/2)
• Many different MPUs are produced by many
different IC vendors (e.g., Motorola, Intel,
Texas Instruments, Zilog, National
Semiconductors, etc.).
• Major differences are in
– word size,
– the number and types of instructions that can be
performed,
– the types of external control signals available,
– the amount of memory that can be addressed.
Microcontroller
• A microcontroller unit (MCU) contains an
MPU, memory, and I/O circuitry on a single
chip.
• Such a chip can perform control operations
without the need for any external circuitry.
• e.g. PIC16F877
• e.g. Intel 8051
Microprocessor vs microcontroller (1/3)
• Microprocessors: high performance, general
purpose “brains” for PCs and workstations
– Instruction decode and control, arithmetic/logic
operations, registers, timing, external control
– Typical cost: $75 -- $500
– Annual demand: 10s of millions
• Microcontrollers: devices with high levels of
integration for embedded control
– Microprocessor functions plus on-chip memory
and peripheral functions (e.g. ports, timers)
– "Swiss army knife" of microprocessor technology
– Typical cost: $1-- $25
– Annual demand: billions!
Microprocessor vs microcontroller (2/3)
Microprocessor
ALU
Memory
I/O
Peripheral
functions
Control
Address
Data
Control
Microcontroller
Microprocessor vs microcontroller (3/3)
Not always a clear distinction: today’s mP may be
tomorrow’s mC
• Microprocessor
– Includes memory management unit, lots of cache
– Performance is the most important feature (cost is
important, but secondary)
– Used mainly in desktop machines
• Microcontroller
–
–
–
–
–
Integrated RAM and ROM, no cache
Includes lots of peripherals
Used mainly in “embedded” applications
Often involves real-time control
Important features include: low cost, low power
consumption, number of integrated peripherals,
interrupt response time, amount of RAM and ROM
Bottom-up view of microcontroller
systems (1/3)
Bottom-up view of microcontroller
systems (2/3)
Bottom-up view of microcontroller
systems (3/3)
Microcontroller Use
What will you study in EEE237?
• PIC16F877 is the MCU choice in EEE237
• Why?
– Much easier to use, have attractive features and
suitable for wide range applications
– Harward architecture makes PICs faster
• You will be studying
– how it is programmed to perform various
operations
Embedded System
• Microcontrollers are sometimes called embedded
microcontrollers, which just means that they are
part of an embedded system -- that is, one part of
a larger device or system.
• The majority of microcontrollers in use today are
embedded in other machinery, such as
automobiles, telephones, appliances, and
peripherals for computer systems. These are called
embedded system.
• Typical input and output devices include
switches, relay, solenoids, LEDs, small or
custom LCD displays, radio frequency
devices, and sensors for data such as
temperature, humidity, light level etc.
• Embedded systems usually have no
keyboard, screen, disks, printers, or other
recognizable I/O devices of a personal
computer, and may lack human interaction
devices of any kind.
Microchip PIC
• PIC is a family of Harvard architecture
microcontroller made by Microchip Technology.
The name PIC initially referred to "Peripheral
Interface Controller“ . PIC microcontrollers were
the first RISC microcontroller.
• PICs are popular with both industrial developers
and hobbyists alike due to their low cost, wide
availability, large user base, extensive collection
of application notes, availability of low cost or
free development tools, and serial programming
(and re-programming with flash memory)
capability.
Two Different Architectures
Fetch & Execution Cycles / Pipelining
• There are 35 single word instructions. A two-stage pipeline
overlaps fetch and execution of instructions. As a result, all
instructions execute in a single cycle except for program branches.
These take two cycles since the fetch instruction is “flushed” from
the pipeline while the new instruction is being fetched and then
executed.
• A typical picture of the pipeline is shown below.
Clock And Instruction Cycles
• Clock from the oscillator enters a
microcontroller via OSC1 pin where internal
circuit of a microcontroller divides the clock into
four even clocks Q1, Q2, Q3 and Q4 which do
not overlap.
• These four clocks make up one instruction cycle
(also called machine cycle) during which one
instruction is executed.
• Execution of instruction starts by calling an instruction that
is next in string.
• Instruction is called from program memory on every Q1
and is written in Instruction Register (IR) on Q4.
• Decoding and execution of instruction are done between
the next Q1 and Q4 cycles. The following diagram
shows the relationship between instruction cycle and clock
of the oscillator (OSC1) as well as that of internal clocks
Q1 – Q4.
• Program Counter (PC) holds information about the
address of the next instruction.
Why use PIC16F877?
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Why PIC16F877A is very popular?
This is because PIC16F877A is very cheap. Apart from that
it is also very easy to be assembled. Additional components
that you need to make this IC work is just a 5V power supply
adapter, a 20MHz crystal oscillator and 2 units of 22pF
capacitors.
What is the advantages of PIC16F877A?
This IC can be reprogrammed and erased up to 10,000
times. Therefore it is very good for new product
development phase.
What is the disadvantages of PIC16F877A?
This IC has no internal oscillator so you will need an external
crystal of other clock source.
Features of PIC16F877
Key Features
PIC16F877
MAX Operating Frequency
20MHz
FLASH Program Memory
(14-bit words)
8K
Data Memory (bytes)
EEPROM Data Memory (bytes)
I/O Ports
8
368
256
RA0-5 (6)
RB0-7 (8)
RC0-7 (8)
RD0-7 (8)
RE0-2 (3)
Timers
3
CCP
2
Serial Communications
MSSP, USART
Parallel Communications
PSP
10-bit Analog-to-Digital Module
8 Channels
Instruction Set
35 Instructions
Pins (DIP)
40 Pins
Bubble diagram of PIC16F877
As you can see the PIC16F877A is
rich in peripherals so you can use it
for many different projects.
Pin Diagram of PIC16F877
• Plastic dual in-line
package (DIP)
Pin Diagram of PIC16F877
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Quad Flat Package
(QFP)

Plastic Leaded Chip Carrier Package
(PLCC)
PIC16F877 Internal Block Diagram
• The basic architecture of PIC16F877 consists
of Program memory, file registers and RAM,
ALU and CPU registers.
PIC16F877 Internal Block Diagram
Memory of the PIC16F877
• divided into 3 types of memories:
1. Program Memory – A memory that contains the program (which we
had written), after we've burned it. As a reminder, Program Counter
executes commands stored in the program memory, one after the other.
2. Data Memory – This is RAM memory type, which contains a special
registers like SFR (Special Function Register) and GPR (General Purpose
Register). The variables that we store in the Data Memory during the
program are deleted after we turn of the micro. These two memories have
separated data buses, which makes the access to each one of them very
easy.
3. Data EEPROM (Electrically Erasable Programmable Read-Only
Memory) – A memory that allows storing the variables as a result of
burning the written program.
• Each one of them has a different role. Program
Memory and Data Memory two memories that are
needed to build a program, and Data EEPROM is
used to save data after the microcontroller is turn off.
PIC16F877A
Program Memory
• Is Flash Memory
• Used for storing compiled
code (user’s program)
• Program Memory capacity is
8K x 14 bit  Each location
is 14 bits long
 Every instruction is coded
as a 14 bit word
• PC can address up to 8K
addresses
• Addresses H’000’ and
H’004’ are treated in a
special way
PIC16F877A Data Memory (RAM)
Memory storage for variables
Data Memory is also known as Register File and consists of two
components.
General purpose register file (same as RAM).
Special purpose register file (similar to SFR in 8051).
Addresses range from 0 to 511 and partitioned into 4 banks 
each bank extends up to 7Fh (128 bytes).
The user can only access a RAM byte in a set of 4 banks and
only one bank at a time. The default bank is BANK0.
To access a register that is located in another bank, one should
access it inside the program. There are special registers which
can be accessed from any bank, such as STATUS register.