1. AWIM Series Lawndale High School Experiment 6 Dec, 2017
Digital Logic Theory
AWIM Series
Lawndale High School
Experiment 6
Dec, 2017

2. Number Systems Numbers for Humans The Decimal Number system
Base = 10
Digits are 0-9
Powers of ten for bigger numbers ( )
Ex = 4x x x100 =
Numbers for Computers
The Binary Number system
Base = 2
Digits are 0-1
Powers for bigger numbers ( )
Ex. 54 = 1x25 + 1x24 + 0x23 + 1x22 + 1x21 + 0x20 =
Bit = 1 digit
Byte = 8 Bits
Nibble = 4 Bits
Word = 16 Bits
Octal = 3 Bit group 0-7
Hexadecimal = 4 Bit group (0-9, A-F)

3. Digital Logic Theory
Logic is the fundamental language of the digital world of computers, calculators, digital instruments and digital electronics in general. It is the way machines talk with each other and with humans, providing responses for a given set of input conditions.
The term Logic, as used in this course, is a set of rules defining a predetermined output from a set of known inputs.
The most common logic in use today has two states, On (1or High); or off (0 or Low).
Digital logic today is implemented in multiple technologies, RTL, DTL, TTL, ECL, CMOS, etc.
The basic types of Logic in this course are Invert; AND; OR; NAND; and NOR. Using these basic types in combination can produce other logic functions (R-S and R-S-T Flip-Flops, etc).
In this lesson we will learn the symbols for each type of logic element, how to produce a “Truth Table” for each logic type, learn about Logic Notation and learn how to analyze combinational logic circuits.

4. Digital Logic Theory
Digital Logic has a set of “threshold” voltages. Inputs below the lower threshold are considered a LOW or 0 input, while inputs above the upper threshold are considered a HIGH or 1 input. Voltages between the LOW and HIGH thresholds are ignored.
For the most common logic in use today which uses +5volts for its power (TTL, LS, ALS series), the lower threshold is about +0.4 volts and the upper threshold is about +2.4 volts.
Common Logic gates can have from 2 to 8 inputs.
Logic can be “positive logic” where a “1” is above the high threshold voltage, or “negative logic” where a “1” is below the low threshold voltage.
Logic can be designed to operate at very high speeds; ECL logic can run above 10Ghz.
High speed logic uses lower power supply voltages, 3.3 volts is common.

5. Digital Logic Theory The Invert or “NOT” Gate Element A A IN OUT 11
Truth Table
Invert Symbol A
Input C
Output
Equation C = A
The Invert or NOT function provides the inversion or Opposite of the input.
This function is used alone and in series with other logic elements to form the negative of the element (OR + NOT = NOR).

6. Digital Logic Theory The AND Gate Element A A o B IN A OUT 11
Truth Table
IN B
AND Symbol A
Input C B
Output
Equation C =
A o B
The AND function provides a logic “1” on the output only when Both inputs are logic “1”.
This function is used in all types of logic and with the Invert element forms the NAND element .

7. Digital Logic Theory The NAND Gate Element A A o B IN A OUT 11
Truth Table
IN B
NAND Symbol A
Input
Output C B
Equation C =
A o B
The NAND function provides a logic “0” on the output only when Both inputs are logic “1”.
This function is used in all types of logic circuits.

8. Digital Logic Theory The OR Gate Element A A + B IN A OUT 11
Truth Table
IN B
OR Symbol A
Input
Output C B
Equation C =
A + B
The OR function provides a logic “1” on the output when Either input(s) are logic “1”. If we apply a NOT function to the output, we obtain the NOR gate.
This function is used in all types of logic circuits.

9. Digital Logic Theory The NOR Gate Element A A + B IN A OUT 11
Truth Table
IN B
NOR Symbol A
Input
Output C B
Equation C =
A + B
The NOR function provides a logic “0” on the output when Either input(s) are logic “1”.
This function is used in all types of logic circuits.

10. Digital Logic Theory A IN A IN B OUT 1 B 1 1 Inputs 1 A o B 1 1 11 B 1 1
Inputs 1
A o B 1 1 1
Truth Table C
Output B
C = ( A o B ) + B = A + B
Example 1 – combinational logic

11. Digital Logic Theory
Combinational logic circuit using two NAND gates.
“Set” Input A C
Output C
“Reset Input B
Output
R-S “Set-Reset Flip Flop
This circuit provides a “Bi-Stable” switch function, Alternating from one state to the other based on the inputs.

12. Digital Logic Theory Input Wave-shaping circuit using two NAND gates C
Output C
Output
This circuit changes a Sine wave input into a Square wave using the R-S latch function.

13. Homework - Digital Logic
Name:__________
Date:________
A input of 0.25volts to standard 5v logic equals a “1” T F
The notation for a two input OR gate is A + B T F
Most new automobiles contain digital logic T F
The term TTL stands for Diode-Transistor-Logic T F
A AND gate can have only two inputs T F
A OR gate and a NOT gate can be combined to form a: a) problem gate b) NAND gate c) NOR gate d) Invert gate
If we put NOT gates on both inputs to a two input AND gate we have a: a) NAND gate b) NOR gate c) maybe gate d) water gate
How many input combinations can a Four input AND gate handle: a) 4 b) 16 c) 8 d) 12
What is the normal HIGH Threshold voltage for 5volt logic: a) 1.2 volts b) 5.0 volts c) 3.3 volts d) 2.4 volts

14. Homework - Digital Logic
IN A
IN B
OUT A B 1
Inputs 1 1 1
Truth Table C
Output
C =
Problem 10 – Write the equation for the output of the circuit above and fill in the Truth Table.

15. Homework - Digital Logic
IN A
IN B
IN C
OUT A B 1 1 1 1
Inputs 1 1 1 1 1 1 1 1 D C
Output
Truth Table
D =
Problem 11 – Write the equation for the output of the circuit above and fill in the Truth Table.