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Basic Digital Logic 2Combinational Logic

Paul Godingodinp@telusplanet.netFebruary 2004

Created for the Western Canadian Robotics Society

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Basic Digital Logic 2

Review

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Review

◊ Digital Electronics makes use of 2 states:◊ Logic High, or “1”◊ Logic Low, or “0”

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Review

◊ There are 3 basic digital gates:

◊ AND

◊ OR

◊ NOT

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Review

AND, where ALL inputs must be “1” for the output to be “1”

OR, where ANY of the inputs can be “1” for the output to be “1”

NOT (or the Inverter) where the output is the opposite (compliment) of the input.

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Review Questions

What is the outcome of the following:

1

1

0

1

0

1

1

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Basic Digital Logic 2

Basic Combinational Logic, NAND and NOR gates

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Combinational Logic

◊ A circuit that utilizes more that 1 logic function has Combinational Logic.

◊ As an example, if a circuit has an AND gate connected to an Inverter gate, this circuit has combinational logic.

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Combinational logic

◊ How would your describe the output of this combinational logic circuit?

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NAND Gate

◊ The NAND gate is the combination of an NOT gate with an AND gate.

The Bubble in front of the gate is an inverter.

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Combinational logic

◊ How would your describe the output of this combinational logic circuit?

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NOR gate

◊ The NOR gate is the combination of the NOT gate with the OR gate.

The Bubble in front of the gate is an inverter.

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NAND and NOR gates

◊ The NAND and NOR gates are very popular as they can be connected in more ways that the simple AND and OR gates.

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Exercise 1 – a bit challenging

Complete the Truth Table for the NAND and NOR Gates

Input Output

0 0

0 1

1 0

1 1

Input Output

0 0

0 1

1 0

1 1

NAND NOR

Hint: Think of the AND and OR truth tables. The outputs for the NAND and NOR are inverted.

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Exercise 2 – more challenging

◊ Turn the NAND and NOR gates into inverter (NOT) gates. Include a switch for the input.

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Basic Digital Logic 2

Chips and Gates

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Basic Digital Chips

◊ Digital Electronics devices are usually in a chip format.

◊ The chip is identified with a part number or a model number.

◊ A standard series starts with numbers 74, 4, or 14.◊ 7404 is an inverter◊ 7408 is an AND◊ 7432 is an OR◊ 4011B is a NAND

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Chips

◊ Basic logic chips often come in 14-pin packages.

◊ Package sizes and styles vary.

◊ Pin 1 is indicated with a dot or half-circle

◊ Numbers are read counter-clockwise from pin 1 (viewed from the top)

Pin 1 Pin 7

Pin 14 Pin 8

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Chips

◊ Chips require a voltage to function

◊ Vcc is equal to 5 volts and is typically pin 14

◊ Ground is typically pin 7

Pin 1 Pin 7

Pin 14 Pin 8

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Chips – Specification Sheet

Diagram from http://www.onsemi.com

Voltage

Ground

The voltage and ground pins must be connected for the device to function. Check the specification sheet to make sure.

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Chips – Specification Sheet

Diagrams from http://www.onsemi.com

A

B

C

D

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Wiring a chip

Vcc

Vcc

IN

IN

OUT

Probe

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Useful Resources

◊ Textbooks on Digital Electronics (used is ok!)◊ Electronics Workbench or other electronic simulation

software◊ Craig Maynard’s Virtual Vulcan◊ The following web sites:

◊ http://learnat.sait.ab.ca/ict/digi240_godin/default.htm◊ http://learnat.sait.ab.ca/ict/cmph200/Default.htm◊ http://learnat.sait.ab.ca/ict/cmph200_godin/default.htm

◊ http://focus.ti.com/docs/logic/logichomepage.jhtml◊ http://www.onsemi.com◊ http://www.national.com/

◊ http://www.play-hookey.com/digital/◊ http://www.crhc.uiuc.edu/~drburke/databookshelf.html◊ http://www.digikey.ca/

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Lab Exercise

◊ Using the experimenter’s boards, connect the circuit provided to you in the following pages.

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Layout of the SK-10 Experimenter's Board

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Layout of the SK-10 Experimenter's Board

Flat Side

Wires

7400

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Logic Diagram of Lab

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End of Basic Digital Logic 2

Copyright WCRS and Paul GodinFor non-profit use only