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In mode 2, if N is loaded as the count value, then after (N − 1) cycles, the output becomes low for

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Answer & Explanation

Correct AnswerA. 1 clock cycle

Quick Explanation

In Mode 2 (rate generator), after N counts the output produces a LOW pulse lasting exactly one input clock period, then automatically reloads and repeats. Thus the LOW interval is one clock cycle.

Formula / Key Relation

f_out ≈ f_clk/N

LOW pulse width = 1 clock period

Detailed Explanation

Concept & Reasoning

Mode 2 behaves like a divide-by-N periodic rate generator. OUT is normally HIGH. When the count reaches 1/terminal event, OUT goes LOW for one clock and then returns HIGH as the count reloads. This makes it useful for periodic interrupt or baud-rate generation.

How to Solve It in the Exam

8253/8254 Mode 2 → one-clock LOW pulse every N clocks.

Important Exam Point

Do not confuse Mode 2 with Mode 3 square-wave generator.

Related Revision Path

This question sits in the revision path Microprocessors and Interfacing → 8253/8254 Timer → Operating Modes .

Mode 2 Rate Generator explanatory diagram

Quick Trick

8253/8254 Mode 2 → one-clock LOW pulse every N clocks.

Common Mistake

Assuming LOW lasts N−1 clocks because the output is described after N−1 cycles.

Exam Tip

Do not confuse Mode 2 with Mode 3 square-wave generator.

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Study concept · Mode 2 Rate Generator →Practice concept Practice topic

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