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Transcript
Introduction • Molecules: made up of atoms of individual elements. • Atoms: made up of a nucleus surrounded by orbiting electrons. • Nucleus: made up of protons and neutrons. • Protons: have a positive charge which attract orbiting electrons, which have a negative charge. Introduction • Electric current is when electrons flow from one atom to the next. • Voltage is electrical potential energy. • Ohm’s Law is a fundamental equation in electronics: V = R I; voltage across a component is equal to the current through it multiplied by its resistance. Atomic Structure • Neutron: particle in nucleus of atom having no charge (neutral). • Electron: negatively charged particle orbiting nucleus of atom. • Orbital path: paths of electrons orbiting atom’s nucleus. • Atomic number: number of protons in nucleus of atom. Introduction • Kirchhoff’s Current Law (KCL): explains why current entering a node must equal current leaving node; current cannot be created or destroyed. • Kirchhoff’s Voltage Law (KVL): voltage supplied from one or more sources must be the same amount as voltage dropped across one or more circuit elements. Kirchhoff’s Voltage and Current Laws • Figure 2.4: Two resistors in series. Figure 2.9: Two resistors in parallel. Breadboarding • Breadboard: device with hidden interconnections on which to build prototype circuit. • Trace: copper line on circuit board connecting one component to another; path for current to flow on circuit board. Breadboarding • Simulation: entering a schematic (drawing) of a circuit to test into a computer program which calculates voltages and currents throughout the circuit without physically building the circuit. • Prototype: circuit built functionally the same as a circuit to test. Introduction • Digital electronics is based on the combination and switching of logic levels. • Physically, logic levels are represented by voltages. • Logic levels are usually specified as 0 or 1 (bits). • Each logic level corresponds to a digit in the binary (base 2) number system. Introduction • Time-varying digital waveforms: o Periodic waveforms: repeat a pattern of logic 1s and 0s. o Aperiodic waveforms: do not repeat. o Pulse waveforms: produce a momentary variation from a constant logic level. Digital Versus Analog Electronics • Analog: physical, continuous quantity; analog voltage or current can have any value within a defined range. • Digital: physical quantity by a series of binary numbers; can have only specific discrete values. Digital Logic Levels • Logic level: voltage level that represents a defined digital state in an electronic circuit. • Logic LOW (logic 0): lower of two voltages in a digital system with two logic levels. • Logic HIGH (logic 1): higher of two voltages in digital system with two logic levels. Binary Inputs • Most significant bit (MSB): leftmost bit in binary number; largest positional multiplier. • Least significant bit (LSB): rightmost bit of binary number; smallest positional multiplier. • Truth table: list of output levels of a circuit corresponding to all different input combinations. Decimal-to-Binary Conversion • Sum of Powers of 2: convert decimal number to binary by adding up powers of 2 by inspection, adding bits to fill up total value of number. • Repeated Division by 2: any decimal number divided by 2 will leave a remainder of 0 or 1. Hexadecimal Numbers • Hexadecimal number system: base-16 number system written with sixteen digits, 0–9, and A–F, with power-of-16 positional multipliers. • Hexadecimal (hex) numbers: primarily used as shorthand form of binary notation. Counting in Hexadecimal Table 3.4: Hex Digits and Their Binary and Decimal Equivalents. Digital Waveforms • Digital waveform: series of logic 1s and 0s plotted as a function of time. • Timing diagram: digital waveform, typically with multiple signals on one plot. Periodic Waveforms • Periodic waveforms repeat same pattern of HIGHs and LOWs over specified period of time. • Clock: special case of a symetrical, periodic waveform with a specified frequency. • Time LOW (tl): time during one period that waveform is in LOW state. Periodic Waveforms • Time HIGH (th): time during one period that waveform is in HIGH state. • Period (T): time required for periodic waveform to repeat. • Frequency (f): number of times per second that periodic waveform repeats. • Duty cycle (DC): fraction of total period that digital waveform is in HIGH state. Pulse Waveforms • Pulse: variation of voltage from one logic level to opposite level and back again. • Rising edge: part of a pulse where logic level is in transition from LOW to HIGH. • Falling edge (trailing): part of pulse where logic level is in transition from HIGH to LOW. Basic Logic Functions Figure 4.1: Inverter Symbols Figure 4.2: 2-Input AND Gate Symbol Basic Logic Functions Figure 4.6: 2-Input OR Gate Symbol Figure 4.7: OR Function Represented by Switches in Parallel Basic Logic Functions • Active Level: logic level defined as “ON” state for particular circuit input or output (either HIGH or LOW). • Active LOW: active-LOW terminal considered “ON” when in logic LOW state. • Active HIGH: active-HIGH terminal considered “ON” when in logic HIGH state. Derived Logic Functions Figure 4.12: 2-Input NAND Gate Symbol. Derived Logic Functions Figure 4.13: 2-Input NOR Gate Symbols. Derived Logic Functions Figure 4.18: Exclusive OR (XOR) Gate Symbols Figure 4.19: Exclusive NOR (XNOR) Gate DeMorgan’s Theorems and Gate Equivalence Figure 4.21: NAND Gate and DeMorgan Equivalent (positive and negative NAND) Logic Switches and LED Indicators • LED (Light-Emitting Diode): electronic device that conducts current in one direction only and illuminates when it is conducting. Figure 4.31: Light-Emitting Diode (LED) Enable and Inhibit Properties of Logic Gates • Digital Signal (or Pulse Waveform): series of 0s and 1s plotted over time. • Enable: logic gate is enabled if it allows a digital signal to pass from an input to the output in either true or complement form. • Inhibit (or Disable): logic gate is inhibited if it prevents a digital signal from passing from an input to the output.