Question

A microprocessor scans the status of an output I/O device every 20 ms. This is accomplished by means of a timer alerting the processor every 20 ms. The interface of the device includes two ports: one for status and one for data output. How long does it take to scan and service the device, given a clocking rate of 8 MHz? Assume for simplicity that all pertinent instruction cycles take 12 clock cycles

Answer 1

Answer:

0.0000045 s

Explanation:

f = Frequency = 8 MHz

Clock cycle is given by

$\dfrac{1}{f}=\dfrac{1}{8\times 10^6}=1.25\times 10^{-7}\ s$

Time taken for 12 clock cycles

$12\times 1.25\times 10^{-7}=0.0000015\ s$

Time taken per instruction is 0.0000015 s

In reading and displaying information it requires 3 processes

1 for reading, 1 for searching and 1 for displaying.

$3\times 0.0000015=0.0000045\ s$

Time taken is 0.0000045 s