Subtopics in this chapter
- 2.1Digital logic
- 2.2Combinational and arithmetic circuits
- 2.3Sequential logic circuit
- 2.4Microprocessor
- 2.5Microprocessor system
- 2.6Interrupt operations
What is usually tested
Digital logic questions cover number systems and codes, logic gates, Boolean laws, Karnaugh maps, and the standard building blocks: multiplexers, decoders, encoders, adders, flip-flops, shift registers and counters. The microprocessor part asks about the internal architecture, registers, flags, addressing modes and simple instructions of the 8085 and 8086, memory types and interfacing, the 8255, serial transfer, DMA and the interrupt system.
Sample questions with answers
Choose an answer to check it, or open "Show answer". These 12 are taken from the 150 questions for this chapter in the practice bank.
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The minimum number of 2-input NAND gates required to implement an XOR gate is:
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Answer: B. 4
XOR can be built with 4 NAND gates.
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The hexadecimal number system has a base of:
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Answer: A. 16
Hexadecimal uses sixteen symbols: 0 to 9 and A to F.
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A multiplexer is a circuit that:
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Answer: C. Selects one of several inputs and passes it to a single output
A multiplexer is also called a data selector.
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A multiplexer with eight data inputs needs how many select lines?
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Answer: D. Three
n select lines can choose among 2^n inputs, and 2^3 = 8.
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Which flip-flop toggles its output when both inputs are 1?
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Answer: C. JK
A JK flip-flop toggles when J = K = 1.
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The output of a sequential logic circuit depends on:
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Answer: D. The present inputs and the past state of the circuit
Sequential circuits contain memory elements; combinational circuits do not.
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The Intel 8085 is a microprocessor of:
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Answer: B. 8-bit
8085 is an 8-bit microprocessor with a 16-bit address bus.
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The Program Counter (PC) holds:
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Answer: A. The address of the next instruction
PC stores the memory address of the next instruction to be fetched.
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A memory that loses its contents when the power is switched off is called:
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Answer: A. Volatile memory
RAM is volatile; ROM, flash memory and magnetic disks are non-volatile.
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Dynamic RAM needs periodic refreshing because each bit is stored as:
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Answer: B. Charge on a small capacitor, which leaks away
The charge must be restored every few milliseconds or the data is lost.
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An interrupt is a signal that causes the processor to:
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Answer: A. Suspend the current program and attend to a device or event
After the event has been serviced, the processor resumes the interrupted program.
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The program that is executed in response to an interrupt is called:
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Answer: B. An interrupt service routine
Each interrupt source has its own service routine.
Practise this chapter
The full mock tests mix 10 questions from this chapter with 10 from each of the other nine, under the real 2-hour limit. Chapter practice mode lets you work through this chapter alone, untimed, with the explanation shown after every question. Go to the mock tests