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12. Direct Memory Access Controller: 8257 - An Introduction To Microprocessor 8085

📖 From An Introduction To Microprocessor 8085 • 122 questions available

Practice MCQs for 12. Direct Memory Access Controller: 8257. Test your knowledge with carefully crafted questions across easy, medium, and hard difficulty levels.

🔄 Last updated: 2026-07-30

26
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📝 Sample Questions

Q1. How many 16‑bit registers are provided for each channel in the 8257 DMA controller?

🔹 A. One
🔹 B. Two
🔹 C. Three
🔹 D. Four

💡 Difficulty: easy | ✅ Correct: B

Q2. What is the purpose of the acknowledge (AEN) signal sent by the CPU to an I/O device during a DMA request?

🔹 A. It initiates the transfer of data from the device to memory.
🔹 B. It informs the device that the CPU has released the address and data buses.
🔹 C. It resets the DMA controller after the transfer.
🔹 D. It selects the DMA channel to be used.

💡 Difficulty: medium | ✅ Correct: A

Q3. During a DMA operation on channel 2, the 8257 takes control of the bus. Which of the following best describes the CPU’s activity while the DMA transfer is in progress?

🔹 A. The CPU continues executing instructions using the address bus but not the data bus.
🔹 B. The CPU is halted and does not perform any bus cycles until the DMA controller releases the bus.
🔹 C. The CPU only reads the status of the DMA controller but does not write.
🔹 D. The CPU shares the bus with the DMA controller in a time‑multiplexed fashion.

💡 Difficulty: hard | ✅ Correct: A

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