electronics

Linux Basic Directory Structure*
Basic Terms & Terminology
Electronics refers to the flow of charge (moving electrons) through nonmetal conductors (mainly semiconductors), whereas electrical refers to the flow of charge through metal conductors. For example, flow of charge through silicon, which is not a metal, would come under electronics; whereas flow of charge through copper, which is a metal, would come under electrical.
Propreitary of Vestel Group Of Companies
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* singly (resistor, capacitor, transistor, diode etc.)
* in more or less complex groups as ICs (operational amplifier, resistor array, logic gate etc.)
Electronic Components may be Passive or Active:
Passive Components are those that do not have gain or directionality. They are dumb, and cannot amplify, or dramatically change applied signals. In the Electrical industry they are called Electrical elements or electrical components
Active Components are those that have gain or directionality.
Active parts can clip, amplify, distort or dramatically change applied signals. They include Semiconductors (Solid State Devices) and Thermionic Valves (Vacuum Tubes)
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Oscillators
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* Limits (resists) the flow of electrical current
* value of resistor measured in Ohms.
* Resistors dissipate heat as a result of their opposing electricity, and are therefore rated both in terms of their resistance (how much they oppose the flow of electrons) and their power capacity (how much power they can dissipate before becoming damaged.) Generally, bigger resistors can handle more power.
* Potentiometer = variable resistors, which can have their resistance adjusted by turning a knob or other device.
* V = I x R
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Electronic Devices and Components - Capacitors
* stores electrical energy in the form of an electric field between a pair of conductors (called "plates")
* a capacitor stores voltage as electrical energy
* act as (like) a charge store (small battery)
* Value of capacitor measured in Farads
* capacitors block DC current and let AC current pass
* I = C x dv/dt
* Usage :
* most circuits will place many capacitors accross their
power supplies to decrease overall noise
* Decoupling Capacitors help board elements maintain a stable voltage level supplying more power when needed, helping brownouts.
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* Types of Capacitors
o have very large capacitance per volume unit
o polarized, so must be connected the right way around
o the negative terminal (cathode) is usually marked in some ways.
o can explode violently if connected incorrectly, overheat, or have too much voltage accross them.
o generally, have poor tolerance, and are used mostly where precise capacitance is unimportant such as for power supply smoothing, stiffening, etc.
o Two types of packaging
+ axial
+ radial
* Ceramic Capacitors
o not polarized, doesn't matter which way round they are put in a circuit.
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* Also called “reactor”
* an inductor stores current as magnetic energy.
* block AC current and let DC current pass
* Inductors can have a core of air in the middle of their coils, or a ferrous (iron) core.
* value of inductors measured in Henries
* V = L di/dt
* used extensively in power supplies
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Electronic Devices and Components - Transformers
* couples energy from one side to the other via magnetic field
* the turns ratio determines the ratio of AC voltage
* usage :
* used to isolate signals
a signal from one side is transferred to the other without a common ground
* used to "step up" a voltage
can be used to generate high voltages
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* one-way current switch (gate)
* The side with the line on is the - side
* Current is conducted from the + side to the - side
* Forward voltage drop pf 0.6V and above
* Light Emitting Diode (LED)
* available in many colors
* Usage
* often used in circuits that convert AC to DC, since they can block half the alternating current from passing through
LEDs
* An LED is a diode that is designed to emit light of a particular frequency when current is applied to it.
* They are very useful as status indicators in computers and battery-operated electronics; they can be left on for hours or days at a time because they run on DC, require little power to operate, generate very little heat and last for many years even if run continuously. They are now even being made into low-powered, long-operating flashlights.
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Electronic Devices and Components - Transistors
* At its core, a transistor is an electronic component used in a circuit to control a large amount of current or voltage with a small amount of voltage or current.
* It does so by sandwiching one semiconductor between two other semiconductors. Because the current is transferred across a material that normally has high resistance (i.e. a resistor), it was a "transfer-resistor" or transistor.
* Act as a an electronic switch
* Two basic types :
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Devices to make electrical connection
* Terminal
* Connector
o Header
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* Wires
* Cables
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* Terminal
* Connector
o Header
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* Power cord
* Data Cable
* Patch cord
* Test lead
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Components that may be made to either conduct (closed) or not (open)
* Switch - manually operated switch
* Keypad - small array of pushbutton switches
* Relay - Electrically operated switch. This is a mechanical component, unlike the Solid State Relay
* Reed switch - Magnetically activated switch
* Thermostat - Thermally activated switch
* Mercury switch
* Centrifugal switch
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* Resistor - fixed value
* Trimmer - Small variable resistor
* Potentiometer, Rheostat - Variable resistor
* Resistance wire - wire of high-resistance material, similar to heating element
* Thermistor - Temperature-varied resistor
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Passive components that protect circuits from excessive currents of voltages
1. While these components technically belong to the Wire, Resistor and Vacuum classes, they are grouped here based on their use.
2. Active components that perform a protection function are in the Semiconductor class, below.
* Fuse - Over-current protection, one time use
* Resettable fuse (PolySwitch, self-resetting fuse)- Over-current protection, resettable
* Metal Oxide Varistor, Surge Absorber (MOV) - Over-voltage protection. These are passive components, unlike the TVS
* Inrush current limiter - protection against initial Inrush current
* Gas Discharge Tube - protection against high voltage surges
* Circuit Breaker - Over-current activated switch
* Spark gap - two electrodes with a gap in between too create arcing
* Filament lamp
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* Capacitor - fixed capacitance
* Capacitor network (array)
* Varicap diode - variable capacitor come diode
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* Inductor, coil, choke
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Components that use more than one type of passive component
* RC network - forms an RC circuit, used in Snubbers
* LC Network - forms an LC circuit, used in tuneable transformers and RFI filters
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Passive components that use piezoelectric effect
* Components that use the effect to generate or filter high frequencies
o Crystal - Is a quartz crystal used to generate precise frequencies (See the Modules class below for complete oscillators)
o Ceramic resonator - Is a ceramic crystal used to generate semi-precise frequencies
o Ceramic filter - Is a ceramic crystal used to filter a band of frequencies such as in radio receivers
o Surface Acoustic Wave (SAW) filters
* Components that use the effect as mechanical Transducers.
o Ultrasonic motor - Electric motor that uses the piezoelectric effect
o For piezo buzzers and microphones, see the Transducer class below
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* Fuel cell - an electrochemical generator
* Power supply - usually a mains hook-up
* Photovoltaic device - generates electricity from light
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Cords = Cables with connectors or terminals at their ends
* Power cord
* Patch cord
* Test lead
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Electronic Devices and Components - Switches
Components that may be made to either conduct (closed) or not (open)
* Switch - manually operated switch
* Keypad - small array of pushbutton switches
* Relay - Electrically operated switch. This is a mechanical component, unlike the Solid State Relay
* Reed switch - Magnetically activated switch
* Thermostat - Thermally activated switch
* Mercury switch
* Centrifugal switch
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Passive components that protect circuits from excessive currents or voltages
1. While these components technically belong to the Wire, Resistor and Vacuum classes, they are grouped here based on their use.
2. Active components that perform a protection function are in the Semiconductor class, below.
* Metal Oxide Varistor, Surge Absorber (MOV) - Over-voltage protection. These are passive components, unlike the TVS
* Inrush current limiter - protection against initial Inrush current
* Gas Discharge Tube - protection against high voltage surges
* Circuit Breaker - Over-current activated switch
* Spark gap - two electrodes with a gap in between to create arcing
* Filament lamp
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Electronic Devices and Components - Protection devices - Fuse
* a device designed to protect other components from accidental damage due to excessive current flowing through them. Each type of fuse is designed for a specific amount of current. As long as the current in the circuit is kept below this value, the fuse passes the current with little opposition. If the current rises above the rating of the fuse--due to a malfunction of some sort or an accidental short-circuit--the fuse will "blow" and disconnect the circuit. Fuses are the "heroes" of the electronics world, literally burning up or melting from the high current, causing a physical gap in the circuit and saving other devices from the high current. They can then be replaced when the problem condition has been corrected. All fuses are rated in amps for the amount of current they can tolerate before blowing; they are also rated for the maximum voltage they can tolerate. Always replace a blown fuse only with another of the same current and voltage rating.
* Fuse - Over-current protection, one time use
* Resettable fuse (PolySwitch, self-resetting fuse)- Over-current protection, resettable
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Electrical components that use magnetism
* Inductor, coil, choke
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Components that use more than one type of passive component
* RC network - forms an RC circuit, used in Snubbers
* LC Network - forms an LC circuit, used in tuneable transformers and RFI filters
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Passive components that use piezoelectric effect
* Components that use the effect to generate or filter high frequencies
o Crystal - Is a ceramic crystal used to generate precise frequencies (See the Modules class below for complete oscillators)
o Ceramic resonator - Is a ceramic crystal used to generate semi-precise frequencies
o Ceramic filter - Is a ceramic crystal used to filter a band of frequencies such as in radio receivers
o Surface Acoustic Wave (SAW) filters
* Components that use the effect as mechanical Transducers.
o Ultrasonic motor - Electric motor that uses the piezoelectric effect
o For piezo buzzers and microphones, see the Transducer class below
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Sources of electrical power
* Fuel cell - an electrochemical generator
* Power supply - usually a mains hook-up
* Photo voltaic device - generates electricity from light
* Thermo electric generator - generates electricity from temperature gradients
* Electrical generator - an electromechanical power source
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Electronic Devices and Components - Transducers, sensors, detectors
1. Transducers generate physical effects when driven by an electrical signal, or vice-versa.
2. Sensors (detectors) are transducers that react to environmental conditions by changing their electrical properties or generating an electrical signal.
3. The Transducers listed here are single electronic components (as opposed to complete assemblies), and are passive (see Semiconductors and Tubes for active ones). Only the most common ones are listed here.
* Audio (see also Piezoelectric devices)
* o Loudspeaker - Magnetic or piezoelectric device to generate full audio
o Buzzer - Magnetic or piezoelectric sounder to generate tones
* Position, motion
o Linear variable differential transformer (LVDT) - Magnetic - detects linear position
o Rotary encoder, Shaft Encoder - Optical, magnetic, resistive or switches - detects absolute or relative angle or rotational speed
o Inclinometer - Capacitive - detects angle with respect to gravity
o Motion sensor, Vibration sensor
o Flow meter - detects flow in liquid or gas
* Force, torque
o Accelerometer - Piezoelectric - detects acceleration, gravity
* Thermal
o Thermocouple, thermopile - Wires that generate a voltage proportional to delta temperature
o Thermistor - Resistor whose resistance changes with temperature, up PTC or down NTC
o Resistance Temperature Detector (RTD) - Wire whose resistance changes with temperature
o Bolometer
o Thermal cutoff - Switch that is opened or closed when a set temperature is exceeded
* Magnetic field (see also Hall Effect in semiconductors)
o Magnetometer, Gauss meter
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R Resistor
C Capacitor
L Inductor
RLY Relay
XTAL Crystal
BR Bridge Rectifier
W Wire, cable
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* made from many transistors
* Usage :
IC Generations
Analog ICs
Digital ICs
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* Central Processing Unit (CPU)/Processor
* Programmable Gate Arrays (PGA)
* Field-Programmable Gate Array (FPGAs)
* Programmable Logic Device (PLD)
* IP Cores/Blocks (logic core)
* soft cores : represented as (gate) netlists, HW Desc. Langs. (Verilog, VHDL)
* hard cores : represented a transistor-layout format
foundry = ?
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* Optoelectronics
o Opto Switch, Opto Interrupter, Optical Switch, Optical Interrupter, Photo switch, Photo Interrupter
o LED Display - Seven-segment display, Sixteen-segment display, Dot matrix display
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COFDM Decoder, QAM Decoder, MPEG Decoder
Video Decoder
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Solid State Component = Electronic control components with no moving parts.
Semiconductors
* a solid material that has electrical conductivity in between a conductor and an insulator; it can vary over that wide range either permanently or dynamically.
* Silicon is used to create most semiconductors commercially, but dozens of other materials are used as well.
* Doping
o The property of semiconductors that makes them most useful for constructing electronic devices is that their conductivity may easily be modified by introducing impurities into their crystal lattice. The process of adding controlled impurities to a semiconductor is known as doping. The amount of impurity, or dopant, added to an intrinsic (pure) semiconductor varies its level of conductivity. Doped semiconductors are often referred to as extrinsic.
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solder (lehim, lehimlemek)
a fusible metal alloy with a melting point or melting range of 90 to 450 °C, used in a process called soldering where it is melted to join metallic surfaces. It is especially useful in electronics and plumbing. Alloys that melt between 180 and 190 °C are the most commonly used.
Solder mask
* Solder mask or solder resist is a lacquer (leke, vernik, cila) like layer of polymer that provides a permanent protective coating for the copper traces of a printed circuit board (PCB) and prevents solder from bridging between conductors, thereby preventing short circuits. Solder mask was created primarily to facilitate wave soldering used in mass assembly. The solder mask is most often applied with a green tint but is available in a wide variety of colors and finishes. It also provides some protection from the environment.
Soldering
Iron
* helps solder to "stick"
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Perf boards
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* converts DC to AC
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* converts AC to DC
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Electronics are subatomic particles with a negative charge.
They are bound to positively charges atomic nuclei through coulombic atraction.
Substances are either conductors, insulators, or semiconductors.
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Current
For an electron to move through a conductor, there must be a "vacancy" at the next nucleus into which it can shift. Semiconductor physicists term these vacancies as holes. An electron shifting into a neighboring hole leaves a new hole behind it. This new hole is then filled by another electron further down the line, which in turn, creates another new hole. So current flow is, in effect, a movement of electrons in one direction and a "movement of holes" in another. The electrons are negatively charged, and the holes a may be thought of as positive charges. So while electrons move from negative to positive, the holes move from positive to negative, and it is the movement of holes that we refer to when we talk about the current.
In reality, electrons flow from the negative (-ve) terminal to the positive (+ve) terminal of the supply and for ease of circuit understanding conventional current flow assumes that the current flows from the positive to the negative terminal.
The flows of electrons through a conductor or semiconductor is known as "current"
Current is measured in "Amperes" (also called "Amps"), and has a unit symbol of "A"
Types of current
Current that flows in a single direction is called "Direct Current", or D.C. and current that alternates back and forth through the circuit is known as "Alternating Current", or A.C
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Voltage
For current flow to occur between two points, an imbalance must exist between electrons at one end and holes at the other end. The size of this imbalance is known as the "potential difference", "voltage difference" between two points or Electromotive Force, (EMF).
The unit of voltage difference is the "Volt" (unit symbol V).
A constant voltage source is called a "DC Voltage" with a voltage that varies periodically with time is called an "AC voltage."
Voltage is always measured as the difference between any two points in a circuit and the voltage between these two points is generally referred to as the "Voltage drop".
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Resistance
Ω
The amount of resistance determines whether the circuit is a "good conductor”- low resistance, or a "bad conductor" - high resistance. Low resistance, for example 1Ω or less implies that the circuit is a good conductor made from materials such as copper, aluminium or carbon while a high resistance, 1MΩ or more implies the circuit is a bad conductor made from insulating materials such as glass, porcelain or plastic. A "semiconductor" on the other hand is a material whose resistance is half way between that of a
good conductor and a good insulator such as silicon and germanium and is used to make Diodes and Transistors etc.
For very low values of resistance, for example milli-ohms, (mΩ´s) it is sometimes more easier to use the reciprocal of resistance (1/R) rather than resistance (R) itself. The reciprocal of resistance is called Conductance, symbol (G) and it is the ability of a conductor or device to conduct electricity with high values of conductance implying a good conductor and low values of conductance implying a bad conductor. The unit of conductance is the Siemen, symbol (S).
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Electromagnetic Waves
The electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation.
Heinrich Hertz
Electromagnetic spectroscopy is the the branch of physics in which the spectra of radiation absorbed and emitted by matter is used to obtain information about matter.
Electromagnetic Radiation (EMR)
a self-propagating wave in space or through matter.
photons traveling in a wave-like pattern at the speed of light.
EM radiation has an electric and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy propagation.
Electromagnetic Equations
each photon contains a certain amount (or bundle) of energy (quanta)
wave speed (c) = frequency x lambda (wavelength)
c (speed of light) = 3 x 10^8 m/s
E = h x frequency = h x c / lambda (wavelength)
E = Electromagnetic Energy
Electromagnetic Field (EMF)
Spectral Power Distribution = Spectrum
energy, wavelength, frequency (cycles/sec)
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Voltage
Phase
Baseband describes signals and systems whose range of frequencies is measured from zero to a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies starting at zero. It can often be considered as synonym to lowpass, and antonym to passband. Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated. Signal Rate
Bandwidth Signal to Noise Ratio = SNR = S/N Ratio of Signal Power wrt Noise = 10 log (P signal / P noise)
(Shannon’s) Channel Capacity in the presence of noise there is a limit to the bit rate that a channel can carry
C = BW log 2 (P signal / P noise) (in bits/s)
Unipolar signal
Bipolar signal
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DC component = is the fixed voltage of the signal
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Signal Processing is the analysis, interpretation, and manipulation of signals.
Signals of interest include sound, images, biological signals such as ECG, radar signals, and many others. Processing of such signals includes filtering, storage and reconstruction, separation of information from noise (for example, aircraft identification by radar), compression (for example, image compression), and feature extraction (for example, speech-to-text conversion).
In communication systems, signal processing only occurs at OSI layer 1, the physical layer (modulation, equalization, multiplexing, radio transmission, etc) in the seven layer OSI model, as well as at OSI layer 6, the presentation layer (source coding, including analog-to-digital conversion and data compression).
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Signal Classification
Signals are electrical representations of time-varying or spatial-varying physical quantities, either analog or digital, and may come from various sources. In the context of signal processing, arbitrary binary data streams are not considered as signals, but only digital signals that are representations of analog physical quantities.
For analog signals, signal processing may involve the amplification and filtering of audio signals for audio equipment or the modulation and demodulation of signals for telecommunications. For digital signals, signal processing may involve digital filtering and compression of digital signals.
Analog signal processing — for signals that have not been digitized, as in classical radio, telephone, radar, and television systems
Discrete-time signal processing – for signals that are defined only at discrete points in time, and as such are quantized in time, but not magnitude. This theoretical discipline establishes the mathematical basis for digital signal processing, the technology of processing signals that are quantized in time and magnitude.
Digital signal processing — for signals that have been digitized. Processing is done by general-purpose computers or by digital circuits such as ASICs , FPGAs , or specialized digital signal processors (DSP chips).
Mixed Signal Processing
Audio signal processing — for electrical signals representing sound, such as speech or music
Speech signal processing — for processing and interpreting spoken words
Image processing — in digital cameras, computers, and various imaging systems
Video processing — for interpreting moving pictures
Array processing — for processing signals from arrays of sensors
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The Fourier Transform
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Analog Circuits
Most analog electronic appliances, such as radio receivers, are constructed from combinations of a few types of basic circuits. Analog circuits use a continuous range of voltage as opposed to discrete levels as in digital circuits.
The number of different analog circuits so far devised is huge, especially because a 'circuit' can be defined as anything from a single component, to systems containing thousands of components.
Analog circuits are sometimes called linear circuits although many non-linear effects are used in analog circuits such as mixers, modulators, etc. Good examples of analog circuits include vacuum tube and transistor amplifiers, operational amplifiers and oscillators.
Sometimes it may be difficult to differentiate between analog and digital circuits as they have elements of both linear and non-linear operation. An example is the comparator which takes in a continuous range of voltage but puts out only one of two levels as in a digital circuit. Similarly, an overdriven transistor amplifier can take on the characteristics of a controlled switch having essentially two levels of output.
Digital circuits
Digital circuits are electric circuits based on a number of discrete voltage levels. Digital circuits are the most common physical representation of Boolean algebra and are the basis of all digital computers. To most engineers, the terms "digital circuit", "digital system" and "logic" are interchangeable in the context of digital circuits. In most cases the number of different states of a node is two, represented by two voltage levels labeled "Low"(0) and "High"(1). Often "Low" will be near zero volts and "High" will be at a higher level depending on the supply voltage in use.
Computers, electronic clocks, and programmable logic controllers (used to control industrial processes) are constructed of digital circuits. Digital Signal Processors are another example.
Building-blocks:
Highly integrated devices:
Mixed-signal circuits
Some analog circuitry these days may use digital or even microprocessor techniques to improve upon the basic performance of the circuit. This type of circuit is usually called "mixed signal."
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* Emitter coupled logic (ECL) also known as Current-mode logic (CML)
o Positive emitter-coupled logic (PECL)
o Low-voltage positive emitter-coupled logic (LVPECL)
* Transistor–transistor logic (TTL) and variants
* P-type metal–oxide–semiconductor logic (PMOS)
* N-type metal–oxide–semiconductor logic (NMOS)
* Complementary metal–oxide–semiconductor logic (CMOS)
* Bipolar complementary metal–oxide–semiconductor logic (BiCMOS)
* Integrated injection logic (I2L)
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Latch
Flip-flop
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output E: exactly 2 true
output F: all true
Zero and One Laws: A + 1 = 1, A * 0 = 0
Inverse Laws: A + ~A = 1, A * ~A = 0
Commutative Laws: A + B = B + A, B * A = A * B
Associative Laws: A + (B + C) = (A + B) + C, A * (B * C) = (A * B) * C
Distributive Laws: A * (B + C) = (A * B) + (A * C), A + (B * C) = (A + B) * (A + C)
De Morgan Laws: ~(A + B) = ~A * ~B, ~(A*B) = ~A + ~B
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~(~A + B)
universal - any logic function can be build with only those
NOR Universal
NAND Universal
Combinational Logic
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Digital Circuits
Clock Signal
In (especially) synchronous digital circuits, a clock signal is a signal used to coordinate the actions of two or more circuits. A clock signal oscillates between a high and a low state, normally with a 50% duty cycle, and is usually in the form of a square wave. Circuits using the clock signal for synchronization may become active at either the rising edge, falling edge, or both edges of the clock cycle; for example, DDR SDRAM is activated by both edges.
Self-clocking Signal
a self-clocking signal is one that can be decoded without the need for a separate clock signal or other source of synchronization . This is usually done by including embedded synchronization information within the signal, and adding constraints on the coding of the data payload such that false synchronization can easily be detected.
, Most line codes are designed to be self-clocking.
Examples of self-clocking signals include:
Isochronous:
Manchester code , where the clock signals occur at the transition points.
Most of these codes can be seen as a kind of Run Length Limited code. Those constraints on "runs" of zeros and "runs" of ones ensure that transitions occur often enough to keep the receiver synchronized.
Such self-clocking signals can be decoded correctly into a stream of bits without bit slip .
To further decode that stream of bits and decide which bit is the first bit of a byte, often a self-synchronizing code is used.
Dut Cycle
Rise time
Clock Edge
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Digital Circuits
Dut Cycle
used to describe the fraction of time that a system is in an active state. In particular, it is used in the following contexts: Duty cycle is the proportion of time during which a component, device, or system is operated.
In a periodic phenomenon, the ratio of the duration of the phenomenon in a given period to the period. D = τ/T
where
Τ is the period of the function.
Rise time
When describing a voltage or current step function, rise time refers to the time required for a signal to change from a specified low value to a specified high value. Typically, these values are 10% and 90% of the step height.
The output signal of a system is characterized also by fall time: both parameters depend on rise and fall times of input signal and on the characteristics of the system.
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Digital Circuits
Clock Edge
In electronics, a clock edge is a transition in a clock signal from either low to high (0 to 1) or high to low (1 to 0). It is called an edge because the square wave which represents a clock has edges at those points.
A rising edge is the transition of a digital signal from low to high. It is also named positive edge. When a circuit is rising edge triggered, it becomes active when the clock signal goes from low to high, and ignores the high to low transition.
A falling edge is the high to low transition. It's also known as the negative edge. When a circuit is falling edge triggered, it becomes active when the clock signal goes from high to low, and ignores the low to high transition.
It should be noted that the terms front edge or leading edge, back edge or trailing edge describe the related position of edges in a clock cycle. A leading edge can be a falling edge.
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Digital Circuits
Active high
higher voltage represents a binary “1” or “mark” and the lower voltage represents a binary ”0” or “space”.
By modern convention, digital signals are always active high unless explicitly stated to be active low.
Active low
higher voltage represents a binary “0” or “space” and the lower voltage represents a binary ”1” or “mark”.
The name of an active-low signal is written with a bar above it to distinguish it from an active-high signal.
Most control signals in electronics are active-low signals (usually reset lines, chip select lines and so on). This stems from the fact that most logic families can sink more current than they can source, so fanout and noise immunity increase. (The reason for this is ultimately related to thefact that electrons are negatively charged). It also follows for wired-OR logic if the logic gates are open-collector/open-drain with pull-up resistor. Examples of this are I2C bus and CAN.
RS232 signaling in COM ports, uses active-low signals
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Typical questions that can be answered
* is anything running ?
* is memory getting chip-enable signal ?
* are output signals reasonable ?
* Storage oscilloscope
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* Can track many signals simultaneously
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Hardware emulator that appears to target system as regular microprocessor.
Programmable or controlled by host
Often includes overlay memory that can be used instead of actual memory in the target system
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