Question

The generation of a square wave is possible in the mode

(a) mode 1

(b) mode 2

(c) mode 3

(d) mode 4

The question was asked in semester exam.

This intriguing question comes from Programmable Interval Timer 8254 in chapter Special Purpose Programmable Peripheral devices and their Interfacing of Microprocessor

Answer 1

The correct choice is (c) mode 3

The 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.