pyserial read to USB-to-UART device fails with hw flow control on Windows 10

Question

I have a Silicon Labs CP2102 USB to UART Bridge device. I am writing some python to script writing/reading data to a serial device with pyserial on Windows 10.

It works fine without flow control. However, it fails to read and times out if I enable either DSR/DTR or RTS/CTS.

import serial

ser = serial.Serial()
ser.baudrate = 230400
ser.port = "COM13"
ser.dtr = 1
ser.dsrdtr = True
ser.write_timeout = 1
ser.timeout = 1
ser.open()

n = ser.write(bytes([1]))
n += ser.write(bytes([2]))
n += ser.write(bytes([3]))
print("bytes written ", n)

byte_read = []
byte_read += ser.read(1)
byte_read += ser.read(1)
byte_read += ser.read(1)
print(byte_read)

ser.close()

The same device works fine with TS232 terminal tools, like Termite or TeraTerm, on Windows 10.

It seems like an issue with pyserial.

https://stackoverflow.com/a/19319414/8777946 ```ser.xonxoff=True``` — Misplaced Southerner, Apr 23 '23 at 07:59
xonxoff is for software-based flow control, I am after the hardware-based ones — user97576, May 06 '23 at 14:29

score 0 · Answer 1 · answered May 18 '23 at 17:06

The pyserial documentation appears to allude that hardware flow control is not supported with Windows.

set_output_flow_control(enable)
  Platform: Posix (HW and SW flow control)
  Platform: Windows (SW flow control only)

However, Amulek1416 appears to have come up with a solution that might work if you want to manually toggle the flow control:

import time
import serial

#Since we are doing the RTS and CTS logic ourselves, keep rtscts=False
mySerial = serial.Serial(port='COMX', baudrate=9600, rtscts=False)

# To send some information:

dataToSend = 'HelloWorld!'
mySerial.setRTS(True)

# Wait for CTS signal
while not mySerial.getCTS():
    pass

mySerial.write(bytes(dataToSend, 'ascii'))
time.sleep(0.25) # Wait for the data to have sent before disabling RTS
mySerial.setRTS(False)

pyserial read to USB-to-UART device fails with hw flow control on Windows 10

1 Answers1