On this page
On this page
Troubleshooting checklist
Port does not appear:
- Re-plug the USB device and try another cable or USB port.
- Check Device Manager and install the correct CH340, CP210x, FTDI or vendor driver.
- Confirm the device is powered and not in firmware-update-only mode.
Port cannot open:
- Close other serial tools, IDE monitors and firmware flashing tools.
- Re-check the COM number after device reboot.
- Try unplugging and plugging the adapter again.
Device resets or enters the bootloader when the port opens:
- Clear DTR and, if the board uses it, RTS before opening the port.
- Confirm the board's boot strap sequence and remember that USB adapters may invert the logical signal.
- If
RTS/CTSflow control is enabled, RTS is driver-managed; disable hardware flow control before attempting a manual sequence.
No data received:
- Confirm baud rate, parity, data bits and stop bits.
- Confirm the target device actually sends data or replies to the command.
- Check TX/RX wiring and RS485 A/B wiring.
- Try a known-good command and a slower send interval.
Garbled data:
- Start with baud rate and parity.
- Switch between Text and Hex to decide whether the raw bytes are correct.
- If ASCII is fine and only Chinese, Japanese or Korean characters are wrong, it is a character encoding problem: set the encoding in Receive Setting to the one the device actually uses (GB18030, GBK and Big5 are common on Chinese devices). Receive and send are configured separately.
- If even ASCII is wrong, the cause is usually baud rate or parity rather than encoding — or the device speaks a binary protocol.
RS485 device does not respond:
- Confirm A/B wiring, termination and common ground.
- Make sure only one master is sending.
- Verify device address, function code and CRC.
High baud rate is unstable:
- Shorten the cable and use a better adapter.
- Reduce the display load and enable logging.
- Validate the exact rate before relying on it in long tests.