ECE 171: Introduction to Digital Circuits
Fall 1999
Rev: 9.30.99
Lecture Notes 2
Last Time
Ohm's Law
Power
Kirchoff's Current Law
Resistors in Series
Resistors in Parallel
Resitor Color Codes
Example
Show how to find the voltage, current, and power for each resistor.
This Time
Number Conversions
Logic Gates
Truth Tables
Boolean Expressions
Symbols - Traditional and IEEE/ANSI 1984
Number Conversions
Draw three way diagram to show the six conversions
Decimal <-> Binary
Binary <-> Hex
Hex <-> Decimal
Show how we understand decimal digits as coefficients of powers of 10
Ex: 345,384 = 4 + 8x10 + 3x10^2 + 5x10^3 + 4x10^4 + 3x10^5
Binary to Decimal, vice versa
Binary to Hex, vice versa
Decimal to Hex, vice versa
Show by example
Have students work out examples on their calculators
Physical Logic Gates
Show examples - pass around 7400 ICs
Show overhead of connections and contents
Emphasize that inputs are voltages, not currents
Show that the gates are powered, not passive
One IC contains 4 gates
More details next time
Digital Values
True/False
+5V/0V = GND
On/Off
0/1
High/Low
Logic Gates
Buffer
Tradiational Symbol
IEEE Symbol
Truth Table
Boolean Expression: F = A
Will discuss reason later
Inverters
Traditional Symbol, bubbles
IEEE Symbols: 4 of them, two types of bubbles
Truth table
Expression: F = bar(A)
Bubble Cancellation
OR Gate
Traditional Symbol
IEEE Symbol
Truth table
Expression: F = A + B
And Gate
Traditional Symbol
IEEE Symbol
Truth table
Expression
Alternate representation: OR gate with bubbled inputs & outputs
Do truth table proof that they are equivalent
DeMorgan's Theorem
Show alternate representation of OR gate too
