Primary Programming Constructs

1
Primary Programming Constructs

• Algorithms - a finite sequence of steps for
  solving a logical or mathematical problem or
  performing a task
• Control structures - set of statements, controls
  the execution
• Sequence one statement simply follows another
• Branching program flow depends on which criteria
  are met
• Iteration action is repeated until some
  condition occurs
• Flowcharts a graphic map of an algorithms.
• Pseudo-code brief English description of an
  algorithm

2
English vs. Code

• add two numbers
• (comments from before)
• input first number, input second number,
• add them together, output the result
• 901, 399, 901, 199, 902, 000

3
Program / Algorithm Development

• develop concept (in English)
• sketch control flow of concept
• fill in details
• convert into programming language

4
Three Control Structures

• Sequence
• Branching
• Looping

5
Sequence

• standard operation of a computer
• instructions are executed sequentially (from
  consecutively numbered memory locations)
• program counter increments consecutively through
  memory slots

6
Example of Sequence

• How do we get from here to SkyDome (using the
  TTC)?
• Directions to get to SkyDome are followed in
  sequence

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Flowchart for Sequence
start
end
8
Branching

• allows program execution to depend on input
• example
• if you pass this course, you will get three
  credits
• program
• check to see if you passed
• grant three credits

9
Flowchart for Branching
passed?
grant 3 credits
yes
no
10
New Instructions

• BRANCH 6 mailbox address
• BRANCH ON ZERO 7 mailbox address
• BRANCH ON POSITIVE 8 mailbox address

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Example of Branching

• Assume calculator has value of (YourGrade
  PassingGrade)
• Mailbox Code Meaning
• 20 822 if positive, branch to 22
• 21 630 branch to 30 (skip code to grant
  credits)
• 22 lt code to grant credits gt
• .
  .
• .
  .
• .
  .
• 30 lt remainder of program gt

12
Pseudocode

• Pseudocode is a brief English description of an
  algorithm
• (the comments from before)
• it is not natural English
• it does not have complete detail
• it is not syntactically correct code

13
Grading Example
start
input grade
yes
Honors 85-100 Pass 60-84 Fail 0-59
Honors
85-100
no
yes
Pass
60-84
no
Fail
end
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Grading Example 2

• input grade
• if ( )
• __________________
• else if ( )
• _______________
• else
• ____________

15
Looping

• allows program to repeatedly execute a given
  section
• example
• deal all the cards from the deck
• program
• check to see if there are more cards
• deal a card
• lt repeat gt

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Flowchart for Looping
morecards?
deal a card
yes
no
17
Example of Looping

• Mailbox Code Meaning
• ltassume that calculator value represents number
  of remaining cards gt
• 20 822 if positive, branch to 22
• 21 630 branch to 30 (skip code to deal card)
• 22 lt code to deal cards gt
• .
  .
• .
  .
• 29 620 branch to 20 (repeat until no more
  cards)
• 30 lt remainder of program gt

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Summary

• Programming
• algorithm development coding
• algorithm development requires clarity of thought
• coding requires attention to detail

19
The CPU and Memory
20
Introduction
In a Computer Memory is separate from the
CPU Data is in binary (not decimal)
CentralProcessingUnit
21
System Block Diagram
CPU
Highest Address Memory Lowest Address
ALU
Input/outputinterface
Control unit Program counter
22
The Little Man Computer
23
Components of a CPU

• ALU (arithmetic and logic unit)
• Performs arithmetic and logic operations
• Arithmetic add, subtract, multiply, divide, etc.
• Logic AND, OR, NOT, Shift, etc.
• Control unit
• Interprets instructions
• Controls the flow of information within the CPU
• Works with a program counter (address of next
  instruction)
• Input/output interface
• Provides mechanism for input and output of data
• Many variations possible

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Registers

• A register is a single storage location within
  the CPU
• Unlike memory, which is outside the CPU
• Examples of registers
• Accumulator (ACC)
• Program counter (PC)
• Instruction register (IR)
• Memory address register (MAR)
• Memory data register (MDR)
• Status register
• General purpose registers (R0, R1, )
• Included on some CPUs
• Used for high-speed temporary storage

25
Memory Capacity

• 2n x m bits
• n address bits 2n addresses
• m data bits usually m 8 (for one byte)
• m is the width of the data path
• Typical values
• n 16, 17, 18, 19, 20, 21, 22, etc.
• m 8, 16, 32, 64

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Question

• Q How many bits of memory are contained in a
  memory unit with 512KB of memory?
• A 512 29, K 210, B byte 8 23
• 29 x 210 x 23 222 4,194,304

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Exercise Memory Capacity

• Q How many bits of memory are contained in a
  memory unit with 2MB of memory?
• A

Skip answer
Answer
28
Exercise Memory Capacity

• Q How many bits of memory are contained in a
  memory unit with 2MB of memory?
• A 2 21, M 220, B byte 8 23
• 21 x 220 x 23 224 16,777,216

Answer
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Memory Unit
n bits
Memory cell
bit 0
0 1 2 3 4 2n-1
bit 1
Memory address register
Address decoder
bit n - 1
0 1 2 m - 1
Memory data register
m bits
p. 160
30
MAR-MDR example
31
A visual analogy for memory
32
An individual memory cell
33
Memory Implementations

• RAM random access memory
• Static RAM
• Dynamic RAM
• Both static and dynamic RAM are volatile
• ROM read-only memory
• Nonvolatile and unwritable

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p. 165
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Memory Capacity

• Determined by
• Number of bits in MAR
• Number of bits in the instruction address field
• Types of memory
• Physical
• Logical/Virtual
• Memory content manipulation 4 or 8 bytes

35
Memory Maps

• The usage of memory space on a system is commonly
  depicted in a memory map
• The height of the map is determined by the number
  of addresses
• The width of the map is usually 8 bits
• E.g.,
• a system with a capacity of 216 bytes

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Memory Map
7 6 5 4 3 2 1 0
FFFF 0002 0001 0000
Data bitposition
The bottom of memory
Hexadecimaladdress
37
Use of Memory Maps

• Memory maps are usually drawn to show what is
  where on a system
• The possibilities for what
• RAM, ROM, I/O, nothing
• The possibilities for where
• Determined by the starting/ending addresses for
  each block of RAM, ROM, I/O, nothing
• E.g.,
• a memory map for a system with a capacity of 224
  bytes with two 1 MB RAM modules residing
  consecutively at the bottom of memory.

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Memory Map
FFFFFF 200000 1FFFFF 100000 0FFFFF 00
0000
14 MB empty
224 bytes 16 MB capacity
1 MB RAM
1 MB RAM