1. 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?
2. A breadboard-circuit design using a BCD-to-decimal decoder has a problem wherein the operation of the system is erratic. The technician uses his scope to examine the waveforms throughout the system and doesn't really see any problems. While he's scratching his head, what helpful advice can you offer him as to what might be wrong and what to do to correct the problem?
3. How is the number one (1) indicated on the outputs of a 7447 BCD-to-seven-segment code converter?
4. For the input values (A0–A3, B0–B3, Data Select = 1) given for the circuit given below, what will be indicated on the displays?
5. It is suspected that the comparator in the figure given below has a problem. The inputs are activated in the table shown below and the corresponding outputs noted. What is most likely wrong with the circuit?
For P0 – P3 = 1 and Q0 – Q3 = 0, P > Q = 1, P = Q = 1, P < Q = 0
For P0 – P3 = 0 and Q0 – Q3 = 1, P > Q = 0, P = Q = 1, P < Q = 1
For P0 – P3 = 1 and Q0 – Q3 = 1, P > Q = 0, P = Q = 1, P < Q = 0
6. Which statement best describes the given figure, and what is the function of the terminal labeled EN?
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?
8. The IEEE/ANSI symbol for a decoder has the internal designation bcd/dec. This means the decoder is a:
9. Multiplexing of digital signals is usually required when:
10. Referring to the figure given below, what output code will appear on the output (A3,A2,A1,A0) when the 5 key is pressed?
11. What type of device is shown in the given figure, and what inputs (A3,A2,A1,A0) are required to produce the output levels as shown?
12. What are the outputs of a 7485 four-bit magnitude comparator when the inputs are A = 1001 and B = 1010?
13. Determine the correct output for the multiplexer and its associated timing diagram given below.
14. Which is the decimal number for the BCD number, 10110110?
15. In an AHDL BCD to binary code converter, how is multiplication by 10 accomplished?
16. What is the HDL key issue in the design of the MUX and DEMUX?
17. Why are control inputs included in an HDL magnitude comparator?
18. What VHDL techniques are used to describe a priority encoder?
19. What is an important attribute of the conditional signal assignment statement?
20. There appears to be a problem with a 7-segment display on a DMM sometimes skipping certain numbers. How would you test the display?
21. What is the purpose of a decoder's inputs?
22. Refer to the display multiplexer given below. The MSD display is blank, while the LSD seems to be OK. The input and output lines to the 74157 and 7449 are checked with a scope and can be seen changing levels. The A input on the 74139 also changes; however, the 0 output on the 74139 is always LOW and the 1 output is always HIGH. The B and EN inputs on the 74139 are always LOW. What could cause the problem and what should be done to correct it?
23. The circuit in Figure 9-8 is defective; data is not appearing on the output lines. A check with the scope shows data pulses on the serial data line and multiplex control lines, S0–S2; no parity error is indicated. A further check with a logic probe indicates that Vcc and ground appear to be present. What might be wrong with the circuit?
24. What must be done in the given figure in order to use two 7485 4-bit comparators to compare two 8-bit numbers?
25. A device that selects one of several inputs to be placed on the output is a multiplexer.