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📝 Block Diagram of 8251A in 8085A Microprocessor

📖 From An Introduction To Microprocessor 8085 • 14. Serial Communication and Programmable Communication Interface • 7 questions available

Practice MCQs for Block Diagram of 8251A in 8085A Microprocessor. Test your knowledge with carefully crafted questions across easy, medium, and hard difficulty levels.

🔄 Last updated: 2026-07-30

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Q1. What is the size of the terminal count field that stores the number of bytes to be transferred in the 8257 DMA controller?

🔹 A. 8‑bit

🔹 B. 14‑bit

🔹 C. 16‑bit

🔹 D. 12‑bit

💡 Difficulty: easy | ✅ Correct: B

Q2. Why are the two most significant bits of the terminal count register used to indicate the operation type rather than storing additional count bits?

🔹 A. Because the DMA controller only supports 14‑bit addressing

🔹 B. Because those bits are needed to select read, write, or verify modes

🔹 C. Because the two most significant bits are used to indicate the operation type (read/write) while the lower 14 bits hold the count

🔹 D. Because they are reserved for future expansion and have no current function

💡 Difficulty: medium | ✅ Correct: C

Q3. How does the Data Bus Buffer cooperate with the Read/Write Logic to guarantee correct data direction during a DMA transfer?

🔹 A. The buffer isolates the DMA controller from the CPU, allowing the Read/Write Logic to control bus drivers based on the operation flag

🔹 B. The buffer stores data temporarily while the Read/Write Logic decides whether to increment the address

🔹 C. The buffer converts parallel data to serial form for the Read/Write Logic

🔹 D. The buffer only works during memory‑to‑memory transfers, not I/O transfers

💡 Difficulty: hard | ✅ Correct: A

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🔗 Related Topics

📝 Serial Data Communication IC 8251 in 8085A Microprocessor 📝 Modem IC 8251 in 8085A Microprocessor 📝 Serial Communication Standard IC 8251 in 8085A Microprocessor 📝 Asynchronous Software Approach IC 8251 in 8085A Microprocessor 📝 Programmable Communication Interface IC 8251 in 8085A Microprocessor

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