pySerial与UART转USB转换器通信异常问题求助

Hey there, let's break down this communication issue you're hitting. The fact that an Arduino Mega works as a middleman but direct connections (either PSoC's built-in UART/USB or external FTDI) don't gives us some solid clues to work through. Here are the most likely culprits and steps to fix them:

1. Double-Check Serial Parameter Consistency #

First, make absolutely sure every serial configuration parameter matches between your PSoC, USB converter, and pySerial setup. Even a tiny mismatch (like a stopbit set to 2 instead of 1) can cause silent data loss or garbled streams.

In your pySerial code, explicitly define all parameters instead of relying on defaults:

import serial

# Replace 'COMx' with your actual port (check via Device Manager on Windows or /dev/tty* on Linux/macOS)
ser = serial.Serial(
    port='COMx',
    baudrate=9600,  # Match this exactly to your PSoC's UART baudrate
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_1,
    bytesize=serial.EIGHTBITS,
    timeout=2,  # Adjust based on your data transmission rate
    xonxoff=False,  # Disable software flow control unless PSoC uses it
    rtscts=False,   # Disable hardware flow control unless PSoC uses it
    dsrdtr=False
)

Go back to your PSoC's UART configuration in the PSoC Creator tool and verify every setting matches—including the clock source (a low-precision clock can cause subtle baudrate drift that the Arduino's more robust UART tolerates better).

2. Fix Flow Control Mismatches #

This is a common gotcha. Your PSoC might be configured to use hardware flow control (RTS/CTS) or software flow control (XON/XOFF), but your USB converter or pySerial setup isn't matching it:

• If your PSoC uses hardware flow control: Ensure the RTS/CTS pins are properly wired between the PSoC and USB converter, then set rtscts=True in your pySerial config.
• If you're not using flow control: Double-check that both the PSoC and pySerial have flow control disabled. The Arduino Mega might be ignoring flow control signals entirely, which is why it works as a middleman.

3. Adjust pySerial Buffer and Read Logic #

Sometimes the default pySerial buffer size is too small, or read logic isn't handling continuous data streams correctly. Try these tweaks:

• Increase the buffer size to handle larger bursts of data:

  ser.set_buffer_size(rx_size=4096, tx_size=4096)
  

• Use a loop to read data as it arrives instead of relying on one-shot reads:

  try:
      while True:
          if ser.in_waiting > 0:
              # Read all available data at once
              raw_data = ser.read(ser.in_waiting)
              # Process data (adjust decoding based on your PSoC's output format)
              print(f"Received: {raw_data.decode('utf-8').strip()}")
  except KeyboardInterrupt:
      ser.close()
      print("\nSerial port closed.")
  

• Add ser.flushInput() and ser.flushOutput() at the start of your script to clear any leftover data in the buffers.

4. Verify PSoC's Transmission Logic #

The Arduino Mega acts as a buffer between the PSoC and your laptop, which suggests the PSoC might be sending data too quickly without accounting for the USB link's latency. Try modifying your PSoC code:

• Add small delays between data packets to give the USB converter time to catch up.
• Implement a simple handshake: Have the PSoC wait for an acknowledgment from your laptop (via pySerial) before sending the next packet. This ensures the receiver is ready for more data.

5. Test with a Serial Monitor First #

Rule out pySerial as the issue by using a standalone serial monitor tool (like TeraTerm, PuTTY, or the Arduino Serial Monitor) to connect directly to the PSoC's built-in USB or FTDI converter:

• If the serial monitor has the same flow issues: The problem is with your PSoC's hardware configuration or transmission logic, not pySerial.
• If the serial monitor works fine: The issue is in your pySerial code configuration—double-check the parameters and read logic steps above.

6. Check Hardware Connections and Grounding #

Don't overlook the basics:

• Ensure you've crossed the TX/RX pins correctly (PSoC TX → USB converter RX; PSoC RX → USB converter TX).
• Make sure all devices (PSoC, USB converter, laptop) share a common ground. A floating ground can cause signal interference that corrupts data streams.

内容的提问来源于stack exchange，提问作者Driss Oulad-abbou