Multiple choice

If the timer 8254 is used in a microprocessor, then the counters always count down. To accomplish this, the counters contain which of the following registers?

  1. Serial-in and serial-out

  2. Parallel-in and parallel-out

  3. Parallel-in and serial-out

  4. Serial-in and parallel-out

  5. Clock in at parallel-out and no clock at clock input
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In 8254, one has to provide the initial value in binary form. This value will provide the required delay. At start, this binary value is loaded to the counter. This is done using parallel-in concept of the shift register. The counter counts down and provides the value to 8254 for comparison with zero. For this, a parallel output stream is used. So, the concept of shift registers is parallel-in and parallel-out.

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