For a basic serial communications link (e.g., RS-232 style asynchronous), what is the minimum number of wires required to send data reliably between two devices?

Introduction / Context:
Serial links can use many control signals, but at minimum they need a shared reference and one path in each direction if two-way data is required. Understanding the minimal wiring helps troubleshoot cabling and set expectations for simple null-modem or point-to-point connections.

Given Data / Assumptions:

• Consider a typical asynchronous serial link between two devices.
• No modem control (RTS/CTS, DTR/DSR) is strictly required.
• Goal is basic, reliable data exchange.

Concept / Approach:
Minimal RS-232-style links use three wires: Transmit Data (TXD), Receive Data (RXD), and Signal Ground (GND). TXD of one device connects to RXD of the other (and vice versa), with a shared ground to establish a reference. Although some current-loop or differential interfaces use pairs differently, the canonical minimum for classic single-ended serial is three conductors.

Step-by-Step Solution:
Identify necessary signals: TX, RX, and a common ground.Cross-connect TX↔RX between devices.Confirm that additional hardware flow-control lines are optional for basic operation.

Verification / Alternative check:
Count typical DB-9 connections: pin 2 (RXD), pin 3 (TXD), pin 5 (GND) suffice for simple terminal-to-host links when software flow control (XON/XOFF) is used or flow control is disabled.

Why Other Options Are Wrong:
1 wire: Cannot carry bidirectional data nor establish a reference.

2 wires: Lacks a shared ground in single-ended RS-232; unreliable.

4 wires: Works (adds hardware flow control) but is not the minimum.

None of the above: Incorrect because three wires suffice.

Common Pitfalls:
Confusing RS-232 with differential standards like RS-485 (which use pairs) or assuming hardware flow control is mandatory. For many simple setups, 3-wire null-modem works.

Final Answer:
3