Input-Output Interface

Computer Organization & Embedded System — Input-Output Organization and Multiprocessor, NEC licence examination syllabus (Nepal Engineering Council).

Input-Output Interface: two addressing philosophies

Should I/O devices share the same address space as memory, or get their own?

🗺️ Isolated vs Memory-Mapped I/O

IsolatedI/O devices get their own separate address space, accessed only via special instructions like IN/OUT.

Memory-mappedI/O device registers occupy addresses within the same space as memory, so ordinary load/store instructions can access them. Most modern systems (including your PC) use this approach.

Asynchronous data transfer — strobe and handshaking

🤝 Strobe vs Handshaking

Strobe controlA single control signal telling the receiver "data is ready now" — simple, but no way to confirm the receiver actually got it.

HandshakingFixes this with a two-signal back-and-forth: sender raises "data valid," receiver raises "data accepted" back — guaranteeing reliable transfer regardless of device speed.

💡 Draw the handshaking timing diagram: Data Valid ↑ → Data Accepted ↑ → Data Valid ↓ → Data Accepted ↓. This exact 4-step cycle is what examiners want to see.

Syllabus points

I/O bus vs memory bus
Isolated (I/O-mapped) vs memory-mapped I/O
Asynchronous transfer: strobe, handshaking

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