What should I check if serial output is missing or unreadable?
Match the baud rate, data format and electrical interface on both sides, then inspect the cable and any serial-to-USB adapter. Also confirm whether the reader is sending raw content or a framed protocol message before treating additional bytes as corrupted data.
Why can output differ from the original QR content?
A reader in transparent output mode may send the original content, while a protocol or development mode can add a header, length, device information and check data. Select the mode that matches the host application and use the protocol reference for that model and firmware.
Can repeated scans of the same code behave differently?
Yes. Single-read and interval modes can treat repeated presentation of the same code differently, while a different code may still be accepted immediately. Confirm which modes and repeat intervals are available for the selected reader before defining the user flow.