Answer

Correct option: (ii) Internal clock pulses

Explanation

A timer in a microcontroller is generally driven by the internal system clock or a clock derived from it. It increments its count at regular intervals and is used for generating delays, measuring time intervals, scheduling tasks and producing periodic events.

A counter can instead be configured to count external events or pulses.

Example

If a timer receives a 1 MHz clock, one clock period is:

$$T = \frac{1}{1\,MHz} = 1\,\mu s$$

The timer can therefore measure time by counting these clock periods.

Therefore, the correct answer is (ii).