Andrew S. Tanenbaum (OS) Edition 4 Exercise 5 Question 38 (Page No. 432)

Question

A computer uses a programmable clock in square-wave mode. If a $500\:MHz$ crystal is used, what should be the value of the holding register to achieve a clock resolution of

1. a millisecond (a clock tick once every millisecond)?
2. $100$ microseconds?

Answer 1

a) $500000$

b)$5000$

Explanation:

a) The  frequency of crystal used $=500\;\text{MHz}$

Decrement  in counter $=2\;\text{nsec}$

Register Value$ = \dfrac{1000000}{2}\\=500000$

b) The frequency of crystal used $=500 \; \text{MHz}$

Decrement in counter$=100\; \mu \text{sec}$

$\therefore $Register Value $=\dfrac{\frac{1000000}{2}}{2} \\\\\\=\frac{5000000}{100}\\\\\\=5000$