ETEC 2301 Programmable Logic Devices
Chapter 3
Logic Gates
Shawnee State University
Department of Industrial and Engineering Technologies
Copyright © 2007 by Janna B. Gallaher
The Inverter
Input
Output
0
1
1
0
Logic Symbol
Truth Table
Timing Diagram
Inverter Operation
Logic Expression
The AND Gate
Logic Symbol
A
B
X
0
0
0
0
1
0
1
0
0
1
1
1
Truth Table
Timing Diagram
0*0=0
0*1=0
1*0=0
1*1=1
Boolean Expression
Logic
Expression
The OR Gate
Logic Symbol
A
B
X
0
0
0
0
1
1
1
0
1
1
1
1
Truth Table
Timing Diagram
0+0=0
0+1=1
1+0=1
1+1=1
Boolean Expression
Logic
Expression
The NAND Gate
Logic Symbol
A
B
X
0
0
1
0
1
1
1
0
1
1
1
0
Timing Diagram
Truth Table
Equivalent Operation
A
B
AB = X
0
0
0*0=0=1
0
1
0*1=0=1
1
0
1*0=0=1
1
1
1*1=1=0
The NOR Gate
Logic Symbol
A
B
X
0
0
1
0
1
0
1
0
0
1
1
0
Timing Diagram
Truth Table
Equivalent Operation
A
B
A+B = X
0
0
0+0=0=1
0
1
0+1=1=0
1
0
1+0=1=0
1
1
1+1=1=0
The Exclusive-OR and Exclusive-NOR Gates
Logic Symbols
A
B
X
X
0
0
0
1
0
1
1
0
1
0
1
0
1
1
0
1
ExOR & ExNOR Truth Tables
Timing Diagram
A
B
A ExOR B = X
A
B
A ExNOR B = X
0
0
0 x 0=0
0
0
0 x 0=0=1
0
1
0 x 1=1
0
1
0 x 1=1=0
1
0
1 x 0=1
1
0
1 x 0=1=0
1
1
1 x 1=0
1
1
1 x 1=0=1
Programmable Logic



Large scale integrated circuit with programmable logic
blocks to implement high level logic functions.
Usually based on a Basic AND Array:
Older styles were one-time programmable, newer
technology uses flash memory.
Programmable Logic (continued)

Different vendors use different technologies:
−
Fuse Technology

−
Antifuse Technology


−

Similar to programmable read-only memories
Also one-time programmable
EEPROM Technology


−
Creates a conductive path where none exists
Also one-time programmable
EPROM Technology

−
Metal fuse that was one-time programmable
Similar to programmable read-only memories
Can be re-programmed
SRAM Technology


Uses static ram style storage
Volitile memory – looses information when powered-down
Programmable Logic (continued)

Device Programming
−
Production environments use dedicated programming devices
−
Development environments use development boards
−
Designers use Integrated Development Software along with programmers
and development boards
Fixed-Function Logic

Integrated Circuit Logic Device Families
−
Each family contains basic logic operations (NOT, AND, OR, NAND,
NOR, EXOR, and EXNOR)
−
Two major families use different semiconductor technology:
−
TTL series – uses binary junction transistors

CMOS series – uses MOS transistors
CMOS






74XX and 54XX series of standard fixed-function logic (74 series =
commercial grade, 54 series = military grade)
Voltages: 5, 3.3, 2.5, and 1.8 volt
5 Volt logic: HC & HCT = High Speed, AC & ACT = Advanced
3.3 volt logic: LV & LVC = Low Voltage, ALVC = Advanced
BiCMOS technology: hybrid CMOS and TTL logic family
− 74BCTXX, 74ABTXX, 74LVTXX, and 74ALBXX series
Fixed-Function Logic (continued)

Integrated Circuit Logic Device Families (continued)
−
TTL



5 volt supply only
74XX and 54XX series devices available (74 series = commercial
grade, 54 series = military grade)
Several variations for speeds and power
− 74
− 74S – Schottky TTL – higher speed
− 74AS – Advanced Schottky TTL
− 74LS – Low-power Schottky TTL
− 74ALS – Advanced Low-power Schottky TTL
− 74F – Fast TTL
Types of Fixed-Function Logic Gates

Standard Numbering System:
Quad 2-input NAND
00
Dual 4-input NAND
20
Quad 2-input NOR
02
Dual 2-input AND - 21
21
HEX inverter
04
Triple 3-input NOR
27
Quad 2-input AND
08
Single 8-input NAND
30
Triple 3-input NAND
10
Quad 2 input OR
32
Triple 3-input AND
11
Quad XOR
86
Quad XNOR
266
Performance Characteristics and Parameters

Propagation Delay Time (tp)

DC Supply Voltage (Vcc)

Power Dissipation (PD)
−

Input and Output Logic Levels
−


Product of supply voltage and average current
VIH = High Level Input Voltage, VIL = Low Level Input Voltage
Speed-Power Product (SPP)
−
Measure of the performance of a logic circuit
−
It is the product of the Power Dissipation and the Propagation Delay time
Fan-Out and Loading
−
Maximum number of inputs to other gates that can be connected with
reliable results.