Measure first
Capture the TX waveform with equipment suited to RS232 voltage levels. Measure the shortest stable bit interval across repeated transitions; its reciprocal suggests the baud rate. A logic analyzer decoder can test candidate rates, data bits, parity and stop bits, but its electrical input must be protected or level shifted.
| Consistent framing errors | Candidate rate close but parity/data/stop configuration wrong. |
|---|---|
| Readable fragments with periodic corruption | Timing drift, adapter clock error or wrong framing. |
| Repeated stable byte pattern | Use known headers/ASCII to validate candidate settings. |
Controlled confirmation
- Observe both startup and normal exchanges.
- Test nearby standard rates in offline decoding, not by transmitting.
- Confirm multiple messages and both directions.
- Only send a known-safe query after framing is verified.
Capture methods are covered in RS232 traffic capture. Continue with protocol decoding after settings are known; resolve uncertain wiring through pinout troubleshooting and see the serial pillar.
Provide raw waveforms/captures, measurement setup, connector/pinout and any known text or message pattern.