©2008 The McGraw-Hill Companies, Inc. All rights reserved. Digital Electronics Principles & Applications Seventh Edition Chapter 1 Digital Electronics Roger L. Tokheim ©2008 The McGraw-Hill Companies, Inc. All rights reserved.

INTRODUCTION Analog vs. Digital Why Digital or Analog? Generating a Digital Signal Multivibrators Defining Logic Levels Testing for Digital Signals Using a Logic Probe Mounting ICs

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Analog vs. Digital Analog signal- one whose output varies continuously in step with the input. Example: Analog Digital signal- one whose output varies at discrete voltage levels commonly called HIGH or LOW (1 or 0). Example: Digital HIGH or 1 LOW or 0 Time

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1.A(n) __________ signal is one whose output varies at discrete voltage levels commonly referred to as HIGH or LOW (1 or 0). 2. A(n) __________ signal is one whose output varies continuously in step with the input. 3. A sine wave (sinusoidal waveform) is an example of a(n) __________ signal. 4. A square wave is an example of a(n) __________ signal. digital analog digital

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Why Digital? Data can be stored (memory characteristic of digital). Data can be used in calculations. Compatible with display technologies. Compatible with computer technologies. Systems can be programmed. Digital IC families make design easier.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Why Analog? Most “real-world” events are analog in nature. Analog processing is usually simpler. Analog processing is usually faster. Traditional electronic systems were mostly analog in nature.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1.Most “real world” measurements (like temperature, speed, pressure, etc.) are __________ (analog, digital) in nature. 2. Electronic circuits that store information and make calculations are probably __________ (analog, digital) in nature. 3. Electronic devices that can be programmed and have alphanumeric displays probably contain __________ (analog, digital) circuitry. 4. Traditional circuitry (as in TVs) was probably __________ (analog, digital) in nature. analog digital analog

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Generating a Digital Signal (with Switch) Note: signal goes H, L, H, UNDEFINED, and finally HIGH. Note: signal goes H, L, H, UNDEFINED, and finally HIGH. CAUTION: Switch bounce may cause problems. Debounced Switch HIGH LOW Debouncing Latch time 0 V time HIGH undefined LOW +5 V NOTICE– no switch bounce!!

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Multivibrators One-shot (monostable) - an electronic device that emits a single pulse when triggered. Free-running (astable) - an electronic device that oscillates between two stable states (HIGH and LOW). Commonly called a clock in digital systems. Latch (bistable) - an electronic device that has two stable states (HIGH and LOW) and must be triggered to jump from one to the other. Commonly called a flip-flop. Commonly used as temporary memory.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. One-shot multivibrator Producing a Digital Pulse Press input The PULSE WIDTH is determined by the design of the multivibrator and NOT how long the input pushbutton is pressed. The PULSE WIDTH is determined by the design of the multivibrator and NOT how long the input pushbutton is pressed.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Free-running multivibrator A free-running multivibrator produces a continuous string of digital pulses. Note: This can also be called a clock.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. 1. A(n) __________ (astable, monostable) multivibrator is an electronic device that generates a continuous string of digital pulses. It may also be called a clock or a free- running MV. astable 2. A(n) __________ (astable, monostable) multivibrator is an electronic device that generates a single digital pulse when triggered. monostable 3. A(n) __________ (bistable, monostable) multivibrator is an electronic device that has two stable states. It is also called a flip-flop and is used as a latch to hold data. bistable 4. A(n) __________ (astable, monostable) multivibrator is an electronic device that is sometimes called a one- shot MV. monostable QUIZ

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Defining Logic Levels 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% HIGH LOW HIGH LOW Undefined TTL Family of ICs CMOS Family of ICs Voltage Logic devices interpret input voltages as either HIGH or LOW. TTL or CMOS IC families have their unique voltage profiles. Both TTL and CMOS IC input voltage profiles are shown below. CAUTION: Input voltages in the UNDEFINED region may yield unpredictable results.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. 1. An input voltage of +3.5V to a TTL IC (+5V supply) would be considered a __________ (H, L, undefined) logic level. HIGH 2. An input voltage of +0.5V to a TTL IC (+5V supply) would be considered a __________ (H, L, undefined) logic level. LOW 3. An input voltage of +1V to a CMOS IC (+10V supply) would be considered a __________ (H, L, undefined) logic level. LOW 4. An input voltage of +9V to a CMOS IC (+10V supply) would be considered a __________ (H, L, undefined) logic level. HIGH 5. An input voltage of +1.5V to a TTL IC (+5V supply) would be considered a __________ (H, L, undefined) logic level. undefined QUIZ

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Testing for a Digital Signal LED Output Indicators Logic Probe DMM or VOM Oscilloscope Logic Analyzer

©2008 The McGraw-Hill Companies, Inc. All rights reserved. +5 V 10 k  +5 V 150  Transistor-Driven LED Output Indicator Activate input Switch (mouse click) Activate input Switch (mouse click) Positive voltage at base of transistor Turns on Q1 and LED lights Q1

©2008 The McGraw-Hill Companies, Inc. All rights reserved. 0% 10% 60% 50% 80% 70% 40% 30% 20% 100% 90% HIGH LOW Logic Probe Behavior Versus Logic Levels HIGH LOW TTLCMOS The logic LOW indicator lights.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. 0% 10% 60% 50% 80% 70% 40% 30% 20% 100% 90% HIGH LOW HIGH LOW TTLCMOS Logic Probe Behavior Versus Logic Levels The logic HIGH indicator lights.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. 0% 10% 60% 50% 80% 70% 40% 30% 20% 100% 90% HIGH LOW HIGH LOW TTLCMOS The FLOATING indicator lights. Note: This response varies with the design of the Logic Probe. Logic Probe Behavior Versus Logic Levels

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Logic Probe Dynamic Response The probe toggles between HIGH and LOW.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Probes stretch narrow pulses so they are not missed. The probe toggles between HIGH and LOW. Logic Probe Dynamic Response

©2008 The McGraw-Hill Companies, Inc. All rights reserved. The probe toggles between HIGH and LOW. Logic Probe Dynamic Response Pulse stretching also allows high frequencies to be displayed.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1.A simple handheld instrument for detecting HIGH, LOW, and Undefined digital logic levels is called a __________ (logic analyzer, logic probe). 2. In the lab, a simple LED indicator circuit can be built using a __________ (transistor, voltage comparator) to drive the LED. 3. In CMOS (using a 10V power supply), a voltage of 9V would light the __________ (HIGH, LOW, Undefined) indicator on a logic probe. 4. In TTL (using a 5V power supply), a voltage of 0.2V would light the __________ (HIGH, LOW, Undefined) indicator on a logic probe. logic probe transistor HIGH LOW toggle between HIGH and LOW 5. If the input to a logic probe is 50Hz square wave, the output would __________ (read HIGH, toggle between HIGH and LOW).

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Solder Mounting ICs: Insertion Technology Device leads pass through holes in the circuit board.

©2008 The McGraw-Hill Companies, Inc. All rights reserved. Solder Mounting ICs: Surface Mount Technology Devices placed by automatic equipment Circuit boards cost less (fewer holes) Higher connection density Smaller and less expensive products Difficult to repair

©2008 The McGraw-Hill Companies, Inc. All rights reserved. REVIEW Analog vs. Digital Why Digital or Analog? Generating a Digital Signal Multivibrators Defining Logic Levels Testing for Digital Signals Using a Logic Probe Mounting ICs