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
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
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
Explanation: Mode 0 is also called as interrupt on 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
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 square wave is possible in the mode
a) mode 1
b) mode 2
c) mode 3
d) mode 4
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.
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
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
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
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
Explanation: If the GATE signal is enabled, then the counter starts counting.
10. The control word register contents are used for
a) initialising the operating modes
b) selection of counters
c) choosing binary/BCD counters
d) all of the mentioned
Explanation: The control word register contents are used for
i) initialising 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.
Sanfoundry Global Education & Learning Series – Microprocessors and Micro-controllers.