State whether the following sentences are true or false. (i) With…
2019
State whether the following sentences are true or false. (i) With memory-mapped I/O, a single read line and a single write line are needed on the bus. (ii) With isolated I/O, the address space for I/O is isolated from that for memory.
Answer: A. (i) – True, (ii) – True — ConceptAn address space is a logical set of addresses interpreted within a transaction type; it does not mean a separate bundle of physical address wires.…
- A.
(i) – True, (ii) – True
- B.
(i) – False, (ii) – False
- C.
(i) – False, (ii) – True
- D.
(i) – True, (ii) – False
Attempted by 942 students.
Show answer & explanation
Correct answer: A
Concept
An address space is a logical set of addresses interpreted within a transaction type; it does not mean a separate bundle of physical address wires.
Memory-mapped I/O places device registers in the memory address space and uses memory-style read/write controls. Isolated I/O creates a separate port address space selected by I/O instructions or control signals.
Application
In memory-mapped I/O, memory and I/O transactions use the same read and write control paths, while an address decoder selects either memory or a device register. Therefore one read line and one write line can serve both.
In isolated I/O, the same numerical address can identify an I/O port during an I/O cycle and a memory location during a memory cycle. Separate I/O instructions or control signals select the logical namespace, so the I/O address space remains separate even if the physical address and data bus wires are shared.
Cross-check
Feature | Memory-mapped I/O | Isolated I/O |
|---|---|---|
Logical namespace | I/O registers share the memory address space | I/O ports use a separate address space |
Control selection | Memory read/write controls select the transaction | I/O instructions or control signals select the transaction |
Physical address/data lines | The bus lines may be shared | The bus lines may also be shared; sharing does not merge the logical spaces |
Therefore both statements are true: (i) True and (ii) True.