I/O-mapped addressing — how are devices identified? In classic Intel-style I/O-mapped systems (separate I/O space), input/output devices are identified and selected by assigning each device a specific ________.

Introduction / Context:
Some CPU architectures, such as the 8085 and 8086 families, distinguish between memory space and I/O space. In an I/O-mapped (isolated I/O) scheme, IN and OUT instructions access ports addressed separately from memory. Understanding how devices are identified in this space is key to designing I/O maps and decoders.

Given Data / Assumptions:

• Intel 8085 uses 8-bit port addressing with IN/OUT instructions.
• Memory-mapped I/O (alternative scheme) uses memory addresses instead.
• We focus on the isolated I/O case.

Concept / Approach:
With I/O-mapped I/O on the 8085, each device is selected by an 8-bit port number (0–255). The CPU places this number on the lower address/data bus during I/O cycles, and IO/M along with RD/WR strobes indicate an I/O operation. The decoder then asserts the chip-select for the device assigned to that port, ensuring only the intended peripheral responds.

Step-by-Step Solution:

Verification / Alternative check:
Assembly examples show “IN 20H” or “OUT 10H” addressing ports directly, consistent with 8-bit I/O addressing on the 8085. The 8086 extends capability via DX for 16-bit ports, but the 8085 remains 8-bit.

Why Other Options Are Wrong:

• 16-bit port number: not for the 8085 (that is more associated with 8086/88 using DX).
• 8-bit buffer number and 8-bit instruction: not addressing schemes for isolated I/O.
• 7-bit device ID (I2C): different serial bus protocol, unrelated to 8085 I/O-mapped ports.

Common Pitfalls:

• Mixing isolated I/O with memory-mapped I/O; decoding differs substantially.

Final Answer:
8-bit port number