RS-232: put a transceiver between UART and cable

Applies to: Signal path only. Choose a transceiver and supply circuit from its datasheet; DTE/DCE roles determine the cable wiring.

When to use it

Interfacing a microcontroller with an instrument or legacy serial port.

Why it works this way

The transceiver translates the electrical levels and polarity while the UART handles byte framing.

Connection reference

Make the connection

1. Identify both port roles and whether hardware flow control is required.
2. Use the equipment pinouts to select a straight-through or null-modem cable.
3. Match baud and framing after checking the electrical connection.

Check before powering

• Never apply an RS-232 signal directly to a GPIO input.
• A DE9 shell does not prove a port is RS-232; similar connectors carry CAN and other interfaces.

Sources & review

Source documents inspected; independent electrical and bench review pending. Reviewed 2026-09-27.

• Analog Devices: RS-232 fundamentals
  DTE / DCE and RS-232 electrical interface · checked 2026-09-27

Original writing and diagram by Kal / Valleytech Solutions, CC BY 4.0. Manufacturer artwork and documentation retain their own rights. CC BY 4.0

Continue learning

• UART: TX, RX and a shared reference
• CAN bus: controller, transceiver and termination

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