Exercise: Msi Logic Circuits

Questions for: Msi Logic Circuits

Refer to the keyboard encoder in figure (a). Sometimes when the 5 key is pressed, the system attached to the keypad does not respond. The 5 input on the 74147 is monitored with a digital storage scope while repeatedly pressing the 5 key, and the waveform in figure (b) is obtained; the P above the trace indicates the points at which the technician pressed the key. What is most likely wrong with the circuit?

A:
The switches on the 5 key are intermittent; the contacts need to be cleaned or the switch replaced.
B:
The pull-up resistor connected to the 5 key is bad and should be replaced.
C:
The common ground connection at the bottom of the 0 key has a bad solder connection; repair the connection.
D:
The 74147 is intermittent, possibly due to high temperature, and should be replaced.
Answer: A
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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?

A:
The output is shorted to Vcc; 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.
Answer: B
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One can safely state that the output lines for a demultiplexer are under the direct control of the:
A:
input data select lines.
B:
the internal AND gates.
C:
the internal OR gate.
D:
Input data line.
Answer: A
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Which statement below best describes the function of a decoder?
A:
A decoder will convert a decimal number into the proper binary equivalent.
B:
A decoder will convert a binary number into a specific output representing a particular character or digit.
C:
Decoders are used to prevent improper operation of digital systems.
D:
Decoders are special ICs that are used to make it possible for one brand of computer to talk to another.
Answer: B
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