8051 Architecture — I/O Port Functions Which 8051 I/O port does not have any dual-purpose or alternate function pins and serves only as general-purpose digital I/O?

Introduction / Context:
The classic 8051 has four 8-bit ports named P0, P1, P2, and P3. Several pins have alternate roles such as address/data bus, control strobes, or serial I/O. Knowing which port lines are pure GPIO simplifies interface design and pin planning.

Given Data / Assumptions:

• Standard 8051 pinout is assumed.
• P0 and P2 can support external memory interfacing.
• P3 carries multiple special functions per pin.

Concept / Approach:
Identify ports with multiplexed functions: P0 is AD0–AD7 when external memory is used; P2 is A8–A15; P3 houses control and serial functions (INT, T, RXD, TXD, WR, RD). The only port that remains pure GPIO without built-in alternates is P1.

Step-by-Step Solution:
1) List each port and its known alternates.2) Exclude ports with address/data or control roles.3) The remaining port without alternates is P1, therefore it is the correct answer.

Verification / Alternative check:
Inspect any standard 8051 block diagram and pin table; only P1 lacks an alternate function column.

Why Other Options Are Wrong:

• port 0: Multiplexed address/data bus AD0–AD7.
• port 2: Higher address bus A8–A15 in external memory mode.
• port 3: Special functions such as RXD, TXD, INT0, INT1, T0, T1, WR, RD.

Common Pitfalls:
Confusing the ability to use a port as GPIO with the presence of built-in alternates; although P0 and P2 can be GPIO, they have additional roles that complicate external hardware.

Final Answer:
port 1