PySerial and termios

Diez B. Roggisch deets at
Mon Nov 30 17:15:22 CET 2009

a b wrote:

> I have a pain in the a** problem with pyserial- it works 90% of time
> but on the 10% of time it thorows and termios.error exception with the
> value (5, 'Input/output error') and i cannot get rid of it :(
> The system works as follows:
> A device sends out rs485 data -> rs485 to rs232 converter converts it -
>> an rs232->usb cable attatched to a computer reads the data. Until
> now it hasn't bothered me too much since it hasn't been a lot of data
> (every time i get this exception i unload the pl2303 module from
> kernel, then reload it, open the com port and hope it won't happen
> soon). But now the amount of data is getting bigger and the exceptions
> in the log are quite bothering already so if anyone has a good idea
> what could affect it i'd be very glad...
> oh and the settings for the port opening are:
> self.ser = serial.Serial(self.port, self.baudrate, rtscts=0,
> xonxoff=0, timeout=0)

Did you try a different usb2serial-converter? I've got plenty of them used
in the past few years, and frankly, they mostly suck. Big time.

With them, all kinds of timing-issues and other problems arose, and some
hardware refused to outright work with them.

So, I suggest you try & get a hold on as many usb2serial-converters you can
get from friends and colleagues, and try out which one works best.

There is nothing on the software-side you can do (short from lowering the
bps, as this might cover up for some issues due to relaxed timing. But I
had to cut down to like 2400 bps or some crap like that, which isn't really


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