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Sunday, September 17, 2017

Microprocessor Questions for KERALA PSC Computer Science Exam

1. The interrupt for which the processor has highest priority among all the external interrupts is
a) keyboard interrupt
b) TRAP
c) NMI
d) INT

Answer: c
Explanation: The Non-Maskable Interrupt input pin has the highest priority among all the external interrupts.
2. The interrupt for which the processor has highest priority among all the internal interrupts is
a) keyboard interrupt
b) TRAP
c) NMI
d) INT

Answer: b
Explanation: TRAP is the internal interrupt that has highest priority among all the interrupts except the Divide By Zero (Type 0) exception.
3. In case of string instructions, the NMI interrupt will be served only after
a) initialisation of string
b) execution of some part of the string
c) complete string is manipulated
d) the occurrence of the interrupt

Answer: c
Explanation: When NMI is activated, the current instruction being executed is completed and then NMI is served. In case of string instructions, it is served after the complete string is manipulated.
4. The NMI pin should remain high for atleast
a) 4 clock cycles
b) 3 clock cycles
c) 1 clock cycle
d) 2 clock cycles

Answer: d
Explanation: The NMI pin should remain high for atleast 2 clock cycles and need not be synchronized with the clock for being sensed.
5. The INTR signal can be masked by resetting the
a) TRAP flag
b) INTERRUPT flag
c) MASK flag
d) DIRECTION flag

Answer: b
Explanation: The INTR signal can be masked by resetting the interrupt flag.
6. For the INTR signal, to be responded to in the next instruction cycle, it must go …….. in the last clock cycle of the current instruction
a) high
b) low
c) high or low
d) unchanged

Answer: a
Explanation: The INTR signal must go high in the clock cycle of the current instruction in order to respond in the next instruction cycle.
7. The status of the pending interrupts is checked at
a) the end of main program
b) the end of all the interrupts executed
c) the beginning of every interrupt
d) the end of each instruction cycle

Answer: d
Explanation: At the end of each instruction, the status of the pending interrupts is checked.
8. Once the processor responds to an INTR signal, the IF is automatically
a) set
b) reset
c) high
d) low

Answer: b
Explanation: The IF is automatically reset when the processor responds to an INTR signal. If the processor wants to respond to any type of INTR signal further then, the IF should again be set.
9. If the pin LOCK (active low based) is low at the trailing edge of the first ALE pulse, then till the start of the next machine cycle, the pin LOCK (active low) is
a) low
b) high
c) low or high
d) none of the mentioned

Answer: a
Explanation: The pin LOCK (active low) remains low till the start of the next machine cycle.
10. With the trailing edge of the LOCK (active low), the INTA (active low) goes low and remains in it for
a) 0 clock cycle
b) 1 clock cycle
c) 2 clock cycles
d) 3 clock cycles

Answer: c
Explanation: The INTA (active low) goes low and remains low for two clock cycles before returning back to the high state.

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