The RESET input initializes the DMA controller by clearing command, request and temporary registers and resetting internal sequencing such as the first/last flip-flop. Therefore RESET is the required pin.
Formula / Key Relation
RESET asserted → controller internal state initialized/cleared
Detailed Explanation
Concept & Reasoning
DMA controllers contain internal state that must return to a known condition at system initialization. RESET disables/clears operational state so channels and mode registers can be reprogrammed safely. HOLD/HLDA are bus arbitration signals and do not perform this internal register clearing.
How to Solve It in the Exam
Clear internal controller state → RESET.
Important Exam Point
Differentiate reset/init signals from bus request/acknowledge signals.
Related Revision Path
This question sits in the revision path Microprocessors and Interfacing → DMA Controller → 8237 DMA .
Quick Trick
Clear internal controller state → RESET.
Common Mistake
Choosing HLDA, which only acknowledges a bus hold request.
Exam Tip
Differentiate reset/init signals from bus request/acknowledge signals.
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