Digital Electronics and Systems Flashcards

A PROM (Programmable Read-Only Memory) differs from a ROM in that:

Answer: PROM is programmed by the user after manufacture by blowing fuses

A PROM is shipped with all fuses intact and the user programs it once by selectively blowing fuses with a programmer device.

In Gray code, consecutive values differ by exactly how many bits?

Answer: 1

Gray code is designed so that adjacent values differ by exactly one bit, minimizing errors in mechanical and optical encoders.

What is the function of a priority encoder with 4 inputs?

Answer: Outputs the binary code of the highest-priority active input

A priority encoder evaluates all active inputs and outputs the binary address of the highest-priority (usually highest-numbered) asserted input.

Which flip-flop configuration is used to build a frequency divider that divides input clock frequency by 2?

Answer: D flip-flop with D connected to Q

Connecting Q-bar (Q') back to D causes the D flip-flop to toggle on each clock edge, producing a divide-by-2 output at Q.

In an FPGA, what is the primary programmable logic element?

Answer: Lookup table (LUT)

FPGAs implement combinational logic using Look-Up Tables (LUTs), which are small memories that store truth table outputs for any Boolean function.

What type of logic hazard occurs when a circuit briefly produces an incorrect output pulse during an input transition?

Answer: Glitch (static hazard)

A static hazard (glitch) is a momentary incorrect output spike caused by unequal propagation delays through different logic paths.

The two's complement representation of −7 in 4-bit binary is:

Answer: 1001

+7 = 0111; invert to get 1000, then add 1 = 1001, which is the two's complement representation of −7.