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?
Options
A. The decoder is thermally intermittent; replace it.
B. There is probably a bad connection on the wire wrap protoboard; recheck the wiring.
C. Glitches are probably the culprit; strobe the decoder.
D. The decoder is thermally intermittent and must be replaced; or there is probably a bad connection on the wire wrap protoboard, and the wiring must be rechecked.
Correct Answer
Glitches are probably the culprit; strobe the decoder.
A. A dropping resistor must be used on the CMOS 12 V supply to reduce it to 5 V for the TTL.
B. As long as the CMOS supply voltage is 5 V, they can be interfaced; however, the fan-out of the TTL is limited to five CMOS gates.
C. A 5 V Zener diode must be placed across the inputs of the TTL gates in order to protect them from the higher output voltages of the CMOS gates.
D. A pull-up resistor must be used between the TTL output-CMOS input node and Vcc; the value of RP will depend on the number of CMOS gates connected to the node.
Correct Answer: A pull-up resistor must be used between the TTL output-CMOS input node and Vcc; the value of RP will depend on the number of CMOS gates connected to the node.
9. The input levels to a flip-flop must be maintained for a minimum time period both before and after the edge of the clock signal is applied.