• UART
  • Beginner
  • 5 min
  • Serial CLI

Recipe · Beginner · UART

How to auto-detect an unknown UART baud rate

You found a serial header, but 9600 8N1 is not producing readable text. This recipe uses UART autobaud as a first-pass check before bridging or transmitting anything.

UART autobaud signal traces.
Watch RX timing first, then configure the UART session around the measured baud rate.

Wiring View

BP TXBP RXGNDBP GND
Generated from the wiring summary: to BP.
Step 1

Commands

Run the commands below after selecting the right Bit Pirate mode and confirming the wiring.

Result

What success looks like

You get a stable baud estimate and readable output with read. If the result jumps around, the signal may be idle, inverted, noisy or not UART.

Troubleshooting

  • No common ground between target and Bit Pirate.
  • RX is connected to the wrong side of the link.
  • The signal is inverted or not TTL UART.
  • The target only prints during boot; reset the target while autobaud is running.

Next steps

  • Use read for passive ASCII output.
  • Use raw if the traffic is binary.
  • Connect BP TX and use bridge only after confirming it is safe.

UART autobaud FAQ

What does autobaud measure?

Autobaud estimates the serial rate from transitions seen on the receive line. It is a discovery helper, so the final baud should still be confirmed with readable text or known protocol output.

Should I connect TX before running autobaud?

No. Start with target TX to Bit Pirate RX plus shared ground. Keep Bit Pirate TX disconnected until you know the voltage, baud rate, serial format and whether it is safe to talk to the target.

How should I use autobaud output in the next step?

Treat the detected value as a starting point for UART mode setup, then confirm it with readable output, known prompts or repeated boot messages before moving to bridge or write tests.

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