PEC EPE Computer & Allied flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Two's complement negation

Invert every bit of the number and add one. This represents negative values without a separate sign bit and gives a single representation of zero.

Stack versus heap

The stack stores function calls, locals, and return addresses in LIFO order. The heap stores dynamically allocated memory whose lifetime the programmer controls explicitly.

Pass by reference

The callee receives the address of the caller's variable, so assignments inside the function modify the original. In C this is done with pointers.

Null-terminated string

A character array ending with the null character. Functions like strlen count characters before the terminator, so the array must be one element larger.

De Morgan's theorem

The complement of a product equals the sum of the complements, and the complement of a sum equals the product of the complements. Used to simplify gate networks.

Karnaugh map grouping

Adjacent cells differing in one variable are grouped in powers of two. Larger groups eliminate more variables, and don't-care cells may be included freely.

Setup and hold time

Setup time is how long data must be stable before the clock edge; hold time is how long after. Violating either can cause metastability in the flip-flop.

ALE in 8085

Address Latch Enable signals that the multiplexed AD0-AD7 pins carry a valid low address byte, which an external latch must capture before data appears.

Three-phase power formula

For a balanced load, real power equals the square root of three times line voltage times line current times power factor.

Transformer EMF equation

E equals 4.44 times frequency times turns times peak flux. The 4.44 factor converts a sinusoidal flux waveform to its RMS induced voltage.

Synchronous speed

The rotating field speed equals 120 times frequency divided by pole pairs expressed as poles. An induction rotor runs slightly slower, with slip defined against this speed.

Per-unit system

Actual quantities are divided by chosen base values. Changing base requires scaling impedance by the new-to-old power ratio and the square of the voltage ratio.

Symmetrical components

An unbalanced three-phase set is decomposed into positive, negative, and zero sequences. Only the positive sequence produces net forward torque in a machine.

Differential protection

A relay compares currents entering and leaving a protected zone. Equal currents mean no internal fault; a difference indicates a fault inside the zone.

Distance relay zones

Impedance-measuring relays protect line sections. Zone one covers roughly eighty percent instantly; zone two reaches beyond the line with a deliberate time delay.

Plug setting multiplier

Fault current divided by the product of current transformer ratio and relay plug setting. It locates the operating time on the relay characteristic curve.

Routh-Hurwitz criterion

Counts right-half-plane roots from sign changes in the first column of the Routh array. A zero row is replaced using the auxiliary polynomial from the previous row.

Steady-state error types

A type-zero system has finite step error; type one has zero step error and finite ramp error; type two has zero ramp error.

Percent overshoot

For an underdamped second-order system, overshoot equals one hundred times e raised to minus zeta pi over the square root of one minus zeta squared.

Gain and phase margin

Gain margin is the negative decibel gain at the phase crossover. Phase margin is one hundred eighty degrees plus the phase at the gain crossover.

Virtual short in op-amps

With negative feedback, the ideal op-amp drives its inputs to nearly equal voltage while drawing no input current, enabling simple gain calculations.

Inverting amplifier gain

The closed-loop gain equals negative feedback resistance divided by input resistance. The inverting input stays at a virtual ground.

Nyquist sampling criterion

Sampling must exceed twice the highest signal frequency. Otherwise high frequencies alias into lower bands and cannot be separated afterwards.

RC low-pass cutoff

The minus three decibel frequency equals one over two pi times resistance times capacitance. Each additional pole adds twenty decibels per decade of roll-off.

Full-wave rectifier output

A full-wave rectifier produces average DC equal to twice peak voltage divided by pi, with ripple at twice the supply frequency.

FFT complexity

The fast Fourier transform computes the discrete spectrum in N log N operations instead of N squared, exploiting symmetry and periodicity of the twiddle factors.

Engineer's seal

A seal on drawings certifies competence and responsibility for the work. Applying it to work outside one's competence breaches professional codes.

Conflict of interest

A personal interest that could bias professional judgment. The standard response is prompt disclosure to the employer or client, and withdrawal from the decision.

Whistleblowing conditions

Justified when a serious safety or legal violation threatens the public and internal reporting has failed or is unsafe. Documentation and proper channels matter.

Paramountcy principle

Engineering codes require holding public safety, health, and welfare paramount, ahead of obligations to employers, clients, or personal gain.

Patent requirements

A patent protects a novel, useful, and non-obvious invention for a limited term. Copyright instead protects original expression such as code and drawings.

Negligence elements

A negligence claim requires a duty of care, a breach of that duty, causation linking the breach to harm, and actual damages suffered by the claimant.