8051 Port Count — Parallel I/O Availability How many parallel 8-bit I/O ports are available on a standard 8051 microcontroller?

Introduction / Context:
Knowing the number of available GPIO ports is essential for system pin budgeting. The baseline 8051 exposes multiple 8-bit ports that can be read and written in software for digital interfacing.

Given Data / Assumptions:

• Standard 8051 package and feature set.
• Ports are named P0, P1, P2, P3.
• External memory mode may repurpose some pins, but the count as ports remains unchanged.

Concept / Approach:
The 8051 provides four parallel ports, each 8 bits wide, totaling 32 general purpose lines. Although some pins have alternate roles, software can still configure and read or write port latches as appropriate to the application and hardware wiring.

Step-by-Step Solution:
1) List ports: P0, P1, P2, P3.2) Count them: 4 ports.3) Conclude that there are four parallel ports.

Verification / Alternative check:
Pinout diagrams show 32 I/O lines divided into four groups, even though P0 and P2 may serve the external bus in some designs.

Why Other Options Are Wrong:

• 2 or 3: Underestimate the available ports.
• 5: Exceeds the number present on the baseline 8051.

Common Pitfalls:
Confusing the presence of alternate bus functions with the absence of general purpose I/O capability; overlooking the need for external pull-ups on P0 when used purely as GPIO.

Final Answer:
4