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Old 05-03-2016, 10:42 AM
chrischen chrischen is offline
Junior Member
Join Date: Apr 2016
Posts: 4
Exclamation PySerial issue


I have a premierwave xn communication with a omron PLC through serial port with hostlink protocol.
My script is working fine with sending command to PLC and receive the response from the PLC.

But when I disconnect the serial cable, the script will hang.
Here is my code:

import os
import serial
import datetime

ser = serial.Serial(port = '/dev/ttyS2', bytesize = 7, stopbits = 1, parity = serial.PARITY_EVEN)

def recv(serial):
while True:
buffer = ''
buffer = = 15) #step A
if buffer:
return buffer

def send(data):

command ='@01RR0000000140*\r'

while True:
send (command)
response = recv(ser)

When I disconnect the cable, the script is not dead with exception, it hangs at step A. Even I set a read timeout, it won't return me empty string. It hangs too.
I want to know, how can I make my script work even disconnecting happened.

Thanks and best regards,
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Old 05-12-2016, 01:44 AM
chrischen chrischen is offline
Junior Member
Join Date: Apr 2016
Posts: 4

I have solved this issue. I think the problem is my in my recv function, I put thie in a loop. And after that I put it with the write function in a loop too. That's why when I disconnect, it stuck at reading.
After not put the read in a loop, it works fine now.
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