wiring rs232 interface

RS-232: put a transceiver between UART and cable

Understand why an RS-232 port cannot connect straight to a logic-level UART.

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.

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Connection reference

Layer	Job	Check
MCU UART	TX / RX logic	I/O voltage
RS-232 transceiver	Translate electrical levels	Supply, capacitors, channel direction
Serial cable	Connect endpoints	DTE/DCE and pin-numbered connector views

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.

Matching module references

This is a general interface guide; match your own hardware documentation.

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 · SHA-256: 0d951725f1935e801a58f2d87f3a6dbfbfff5a0aed8832e7b36638265f68aa78

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