Input Output Interfacing Questions and Answers

Q: \(IO/\overline{M}\) signal is generally used for distinguishing between :

The keyed answer is memory mapped IOs and IO mapped IOs.In the 8085, the \(IO/\overline{M}\) line tells external circuits whether the address on the bus belongs to the I/O space or to memory. It is high for IN and OUT instructions, which address ports in the separate I/O space (I/O mapped I/O), and low for memory operations, which include devices placed in the memory address space (memory mapped I/O).It plays no part in telling keyboard input from memory, serial from parallel communication, or synchronous from asynchronous transfers.

\(IO/\overline{M}\) signal is generally used for distinguishing between :

A.Data entry from keyboard and memory device
B.Memory mapped IOs and IO mapped IOs
C.Serial and parallel communication
D.Synchronous and asynchronous data transfers

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: B

The keyed answer is memory mapped IOs and IO mapped IOs.

In the 8085, the \(IO/\overline{M}\) line tells external circuits whether the address on the bus belongs to the I/O space or to memory. It is high for IN and OUT instructions, which address ports in the separate I/O space (I/O mapped I/O), and low for memory operations, which include devices placed in the memory address space (memory mapped I/O).

It plays no part in telling keyboard input from memory, serial from parallel communication, or synchronous from asynchronous transfers.

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Assertion (A) : \(\mathrm{IO}/\overline{\mathrm{M}}\) pin is used to access memory.
Reason (R) : In memory mapped I/O the input/output ports are accessed as memory.

A.Both (A) and (R) are true and (R) is the correct explanation of (A)
B.Both (A) and (R) are true but (R) is not correct explanation of (A)
C.(A) is true but (R) is false
D.(A) is false but (R) is true

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: B

Both (A) and (R) are true but (R) is not the correct explanation of (A).

In the 8085, the \(\mathrm{IO}/\overline{\mathrm{M}}\) signal tells the system whether the current cycle is an I/O or a memory operation: low for memory, high for I/O. So it is used when accessing memory, and the assertion is true.

The reason is also true: in memory-mapped I/O the ports are given memory addresses and are accessed with memory instructions. But that is a different scheme. In memory-mapped I/O this pin is not needed to tell ports from memory, so the reason does not explain why the pin exists.

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Input Output Interfacing Questions and Answers

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