Programmable Logic Device MCQs

Question 1

A 4-bit up/down binary counter is in the DOWN mode and in the 1100 state. To what state does the counter go on the next clock pulse?

Accepted Answer

1011

Answer

1101

Answer

1111

Answer

0000

Question 2

A 4-bit ripple counter consists of flip-flops, which each have a propagation delay from clock to Q output of 15 ns. For the counter to recycle from 1111 to 0000, it takes a total of ________.

Accepted Answer

60 ns

Answer

15 ns

Answer

30 ns

Answer

45 ns

Question 3

The terminal count of a 3-bit binary counter in the DOWN mode is ________.

Accepted Answer

000

Answer

111

Answer

101

Answer

010

Question 4

The hexadecimal equivalent of 15,536 is ________.

Accepted Answer

3CB0

Answer

3C66

Answer

63C0

Answer

6300

Question 5

In an HDL ring counter, many invalid states are included in the programming by:

Accepted Answer

including them under others.

Answer

using a case statement.

Answer

using an elsif statement.

Answer

the ser_in line.

Question 6

In a VHDL retriggerable edge-triggered one-shot, which condition will not exist when a clock edge occurs?

Accepted Answer

The shift register is reset.

Answer

A trigger edge has occurred and we must load the counter.

Answer

The counter is zero and we need to keep it at zero

Answer

The counter is not zero and we need to count down by one.

Question 7

Synchronous (parallel) counters eliminate the delay problems encountered with asynchronous (ripple) counters because the:

Accepted Answer

input clock pulses are applied simultaneously to each stage.

Answer

input clock pulses are applied only to the first and last stages.

Answer

input clock pulses are applied only to the last stage.

Answer

input clock pulses are not used to activate any of the counter stages.

Question 8

List the state of each output pin of a 7447 if RBI = 0, LT = 1, A0 = 1, A1 = 0, A2 = 0, and A3 = 1.

Accepted Answer

RBO = 0, a = 0, b = 0, c = 0, d = 1, e = 1, f = 0, g = 0

Answer

RBO = 1, a = 0, b = 0, c = 0, d = 1, e = 1, f = 0, g = 0

Answer

RBO = 0, a = 0, b = 0, c = 0, d = 0, e = 1, f = 0, g = 0

Answer

RBO = 1, a = 0, b = 0, c = 0, d = 0, e = 1, f = 0, g = 0

Question 9

Three cascaded decade counters will divide the input frequency by ________.

Accepted Answer

1,000

Answer

10

Answer

20

Answer

100