Principles & Applications Digital Electronics Principles & Applications Fifth Edition Roger L. Tokheim Chapter 1 Digital Electronics ©1999 Glencoe/McGraw-Hill

CHAPTER 1 PREVIEW 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

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

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.

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.

GENERATING A DIGITAL SIGNAL (WITH SWITCH) 0 V time HIGH undefined LOW +5 V Note: signal goes H, L, H, UNDEFINED, and finally HIGH. CAUTION: Switch bounce may cause problems. Debounced Switch Debouncing Latch time HIGH LOW

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.

PRODUCING A DIGITAL PULSE One-shot multivibrator The output pulse width is determined by the multivibrator and not how long the button is pressed.

Note: This can also be called a clock. A free-running multivibrator produces a continuous string of digital pulses. Free-running multivibrator Note: This can also be called a clock.

TEST 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 (Left click mouse for next question or answer)

DEFINING LOGIC LEVELS 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. TTL family of ICs CMOS family of ICs HIGH 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% HIGH Voltage Undefined Undefined LOW LOW

TEST 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

TESTING FOR A DIGITAL SIGNAL LED output indicators Logic probe DMM or VOM Oscilloscope Logic Analyzer

TRANSISTOR-DRIVEN LED OUTPUT INDICATOR 150 W 10 kW +5 V

LOGIC PROBE BEHAVIOR VERSUS LOGIC LEVELS TTL CMOS 100% 90% 80% HIGH 70% HIGH 60% 50% 40% 30% 20% 10% LOW LOW 0% The logic LOW indicator lights.

LOGIC PROBE BEHAVIOR VERSUS LOGIC LEVELS TTL CMOS 100% 90% HIGH 80% 70% HIGH 60% 50% 40% 30% 20% LOW LOW 10% 0% The logic HIGH indicator lights.

LOGIC PROBE BEHAVIOR VERSUS LOGIC LEVELS TTL CMOS 100% 90% HIGH 80% 70% HIGH 60% 50% 40% 30% 20% LOW LOW 10% The FLOATING indicator lights. 0% Note: This response varies with the design of the Logic Probe.

LOGIC PROBE DYNAMIC RESPONSE The probe toggles between HIGH and LOW.

LOGIC PROBE DYNAMIC RESPONSE Probes stretch narrow pulses so they are not missed. The probe toggles between HIGH and LOW.

LOGIC PROBE DYNAMIC RESPONSE Pulse stretching also allows high frequencies to be displayed. The probe toggles between HIGH and LOW.

MOUNTING ICs: INSERTION TECHNOLOGY Device leads pass through holes in the circuit board. Solder

SURFACE MOUNT TECHNOLOGY MOUNTING ICs: SURFACE MOUNT TECHNOLOGY Solder Devices placed by automatic equipment Circuit boards cost less (fewer holes) Higher connection density Smaller and less expensive products Difficult to repair