chapter 1 for Computer science introduction to digital logic design and

new presentation

1. Chapter 1
Introduction to Digital Systems
There are basically two ways of representing the numerical value of quantities: analog and digital.
Analog?
Varies over a continuous range of values
Examples of analog quantities : time, pressure, sound.
1
Analog  Continuous

2. Digital?
A discrete set of values.
Varies in discrete (separate) steps.
2
Digital 
Discrete

3. Analog vs Digital
Analog
Use base 10 (decimal)
Represented by 10 different
level : 0,1,2,3,4,5,6,7,8,9
Analog system: A combination
of devices that manipulate
values represented in analog
form
3
Digital
Use base 2 (binary)

Represented by 2 different level:
0 and 1 or low and high.
Digital system: A combination of
devices that manipulate values
represented in digital form.

4. DIGITAL
Digital technology is widely used. Examples:
Computers
Manufacturing systems
Medical Science
Transportation
Entertainment
Telecommunications
Basic digital concepts and terminology are introduced
4

5. The Digital AdvantagesThe Digital Advantages
Advantages of digital
Ease of design
Ease of storage
Accuracy and precision are
easier to maintain
Programmable operation
Less affected by noise
Ease of fabrication on IC
chips
Thus, the systems is more
efficient and reliable:
 Data Processing
 Data Transmission
Data Storage
5
Limitation digitalLimitation digital
There is really only
one major drawback
when using digital
techniques:
“ The real world is
mainly analog”

6. A System Using Digital and Analog
Methods
6

7. Binary Digits = Bit
7
Bit 1 : 2 – 5V(high)
Undefined : 0.8 – 2V
Bit 0 : 0 – 0.8V(low)
0V
0.8V
2.0V
5.0V

8.  Binary Digits
Digital systems use the binary number system.
Therefore, two-state devices are used to represent the two binary
digits 1 and 0 by two different voltage levels, called HIGH and LOW
8
Positive Logic (active
high)
High = 1 (Bit 1)
Low = 0 (Bit 0)
Negative logic
(active low)
High =0
Low =1

9. Examples of digital waveforms of Periodic and Non-
Periodic

9

10. Frequency (f) vs. Period (T)
Frequency (f) is the rate at which it repeat itself at a
fixed interval. Is measured in cycles per second or Hertz
(Hz)
f = 1/Tf = 1/T Hz
Period (T) is the time from the edge of one pulse to
the corresponding edge of the next pulse. Is
measured in second
T = 1/f T = 1/f ss
Example :
clock frequency : f = 100Hz,
so, period : T = 1/100Hz = 0.01s = 0.01x 10
3
= 10 ms

10

11. Unit Conversion
11
F = 100khZ, so
T = 1/f
= 1/(100*10
3
Hz)
= 1/(10
2
*10
3
Hz)
= 1/(10
5
Hz)
= 0.00001 s
= 0.00001 x 10
3
= 0.01 ms
= 0.01 x 10
-3
= 10 µs

12. Pulse Width
Pulse width (t
W): A measure of the duration of the
pulse.
Amplitude
Pulse
Width
Rise Time Fall Time
90%
50%
10%
90%
50%
10%
12

13. Duty Cycle
13
Example : a periodic digital waveform has a pulse width
1ms and period time 10ms, calculate duty cycle?
Duty cycle = 1ms/10ms * 100% = 10%
1

14. Timing Diagram
14
Is a graph of digital waveform showing the actual time
relationship of two or more waveform and how each
waveform changes in relation to the others.

15. 15
12345678
A
B
C
Clock
A, B and C HIGH
A = 1, B = 1, C = 1
A?B?C?
Bit
time 7

16. Data transfer: Serial vs Parallel
16
Serial : 8 clock time
Parallel : 1 clock time

17. Serial vs Parallel
17