The BCD/DEC decoder shown in figure (a) is examined with a logic analyzer and th

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Question
The BCD/DEC decoder shown in figure (a) is examined with a logic analyzer and the results are shown in the waveforms in figure (b). What, if anything, is wrong with the circuit?
Options
A. The "2" output is shorted to V_cc.
B. The A1 input is internally open.
C. The A1 input node is internally stuck LOW.
D. Nothing is wrong with the circuit.

Correct Answer

The A1 input node is internally stuck LOW.

MSI Logic Circuits problems

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1. One can safely state that the output lines for a demultiplexer are under the direct control of the:
Options
A. input data select lines.
B. the internal AND gates.
C. the internal OR gate.
D. Input data line.

2. What is the HDL key issue in the design of the MUX and DEMUX?
Options
A. Having the MUX and DEMUX part of the library
B. Using the case statement in the process
C. Describing the functions
D. Assigning signals under certain conditions

3. How is the number one (1) indicated on the outputs of a 7447 BCD-to-seven-segment code converter?
Options
A. Segment a is active.
B. Segment b is active.
C. Segments a and b are active.
D. Segments b and c are active.

4. There appears to be a problem with a 7-segment display on a DMM sometimes skipping certain numbers. How would you test the display?
Options
A. Remove the display unit and check each segment diode with an ohmmeter. Replace the defective segments.
B. Apply 5 V directly to each segment of the display and check for individual segment operation. Replace any segment that has voltage applied but is not lit.
C. Tie all of the segments together and connect to V_cc; the number 8 should appear on the display. Now check the display supply voltage to determine if the display is receiving the correct voltage.
D. Connect the DMM to a variable supply and very slowly increase the voltage, while observing for missing digits. Then check the segment voltage to determine whether the display or the display driver is bad.

5. A 16-input multiplexer is to be used to perform parallel-to-serial data conversion. Which of the following counters would be required to provide the data select inputs?
Options
A. MOD 8
B. MOD 16
C. MOD 4
D. MOD 2

7. The data transmission system shown in below has a problem; the parity error output is always high. A logic analyzer is used to examine the system and shows that the DATA IN on the left matches the DATA OUT on right. What might be causing the problem?
Options
A. The error gate could be defective.
B. The storage circuit could be defective.
C. The parity checker could be bad.
D. Any of the above.

8. What are the outputs of a 7485 four-bit magnitude comparator when the inputs are A = 1001 and B = 1010?
Options
A. A < B is 1
A = B is 0
A > B is 1
B. A < B is 0
A = B is 1
A > B is 0
C. A < B is 0
A = B is 0
A > B is 1
D. A < B is 1
A = B is 0
A > B is 0

9. Refer to the figure given below. The logic function generator being implemented with the multiplexer in this circuit produces a constant LOW on the output. The ABC inputs are checked and appear to be pulsing; also, the 0?7 and EN inputs are checked with the scope and all appear to be at 0 V. A check with the DMM confirms that power is on. What is the problem, and what should be done to correct it?
Options
A. The output is shorted to V_cc; replace the IC.
B. The scope's vertical input is in the AC mode and the common connection for the 0,2,3 and 5 inputs is bad. Set the scope's vertical input mode to DC, and repair the bad solder connection.
C. Power has not been applied to the circuit; apply power.
D. The output is shorted to ground; replace the IC.

10. Which statement best describes the given figure, and what is the function of the terminal labeled EN?
Options
A. Quad two-input multiplexer. EN is the enable input, which requires an active LOW for the device to work.
B. Quad two-bit multiplier, EN is the active HIGH trigger.
C. Dual quad-input multiplexer, which requires an active LOW on the EN terminal for the device to work.
D. Quad two-input AND gate, which requires an active LOW on the EN input to enable all the gates.

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