Microprocessors Questions and Answers – Programmable Interval Timer 8254

This set of Microprocessor Multiple Choice Questions & Answers (MCQs) focuses on “Programmable Interval Timer 8254”.

1. The number of counters that are present in the programmable timer device 8254 is
a) 1
b) 2
c) 3
d) 4
View Answer

Answer: c
Explanation: There are three counters that can be used as either counters or delay generators.

2. The operation that can be performed on control word register is
a) read operation
b) write operation
c) read and write operations
d) none
View Answer

Answer: b
Explanation: The control word register can only be written and cannot be read.

3. The mode that is used to interrupt the processor by setting a suitable terminal count is
a) mode 0
b) mode 1
c) mode 2
d) mode 3
View Answer

Answer: a
Explanation: Mode 0 is also called as an interrupt on the terminal count.

4. In mode 2, if N is loaded as the count value, then after (N-1) cycles, the output becomes low for
a) 1 clockcycle
b) 2 clockcycles
c) 3 clockcycles
d) 4 clockcycles
View Answer

Answer: a
Explanation: After (N-1) cycles, the output becomes low for only 1 clockcycle. If the count N is reloaded and again the output becomes high and remains so for (N-1) clock pulses.

5. The generation of a square wave is possible in the mode
a) mode 1
b) mode 2
c) mode 3
d) mode 4
View Answer

Answer: c
Explanation: When the count N loaded is even, then for half of the count, the output remains high and for the remaining half it remains low. If the count loaded is odd, the first clock pulse decrements it by 1 resulting in an even count value.
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6. In control word register, if SC1=0 and SC0=1, then the counter selected is
a) counter 0
b) counter 1
c) counter 2
d) none
View Answer

Answer: b
Explanation: SC denotes select counter.

7. In control word format, if RL1=1, RL0=1 then the operation performed is
a) read/load least significant byte only
b) read/load most significant byte only
c) read/load LSB first and then MSB
d) read/load MSB first and then LSB
View Answer

Answer: c
Explanation: To access 16 bit, first LSB is loaded first, and then MSB.

8. If BCD=0, then the operation is
a) decimal count
b) hexadecimal count
c) binary count
d) octal count
View Answer

Answer: b
Explanation: If BCD=0 then hexadecimal count. If BCD=1, then the operation is BCD count.

9. The counter starts counting only if
a) GATE signal is low
b) GATE signal is high
c) CLK signal is low
d) CLK signal is high
View Answer

Answer: b
Explanation: If the GATE signal is enabled, then the counter starts counting.

10. The control word register contents are used for
a) initializing the operating modes
b) selection of counters
c) choosing binary/BCD counters
d) all of the mentioned
View Answer

Answer: d
Explanation: The control word register contents are used for
i) initializing the operating modes (mode 0-mode 4)
ii) selection of counters (counter0-counter2)
iii) choosing binary or BCD counters
iv) loading of the counter registers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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