RS-232 / EIA-232 pinout (DB-25, DTE) For a standard EIA-232 (RS-232C) DB-25 DTE connector, which pin carries the Transmitted Data (TxD) signal from the terminal (DTE) to the modem (DCE)?

Introduction / Context:RS-232 (EIA-232) is a classic serial interface. Correctly identifying signal pins is essential for troubleshooting and cable fabrication. The DB-25 pinout distinguishes transmitted and received data as viewed from Data Terminal Equipment (DTE) such as a computer or terminal.

Given Data / Assumptions:

• Connector type: DB-25 on a DTE device.
• We need the pin carrying Transmitted Data (TxD) from DTE to DCE.
• Conventions follow RS-232C standard assignments.

Concept / Approach:On a DB-25 DTE connector: Pin 2 = TxD (transmitted data out of DTE), Pin 3 = RxD (received data into DTE), Pin 7 = Signal Ground, Pin 4 = RTS, Pin 5 = CTS. Note that DB-9 assignments are different (TxD is Pin 3 on DB-9), which often causes confusion.

Step-by-Step Solution:Identify interface and viewpoint: DB-25 on DTE.Recall canonical mapping: Pin 2 is TxD on DB-25 (DTE side).Confirm that Pin 3 is RxD and Pin 4 is RTS; therefore Pin 2 is the answer.Select “Pin 2.”

Verification / Alternative check:Consult any RS-232 DB-25 DTE pinout: 2-TxD, 3-RxD, 7-GND. Loopback plugs and breakout boxes also confirm signal directions in practice.

Why Other Options Are Wrong:Pin 3: corresponds to RxD on DB-25 DTE; not transmitted data.Pin 4: corresponds to RTS control; not data.All of the above / None: incorrect because only one pin is used for TxD on DB-25 DTE.

Common Pitfalls:

• Mixing DB-9 and DB-25 numbering (DB-9 TxD is Pin 3).
• Forgetting DTE vs. DCE perspective; the directions swap on DCE connectors.
• Assuming proprietary cables follow standards; always verify wiring diagrams.

Final Answer:Pin 2