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<== Date ==> <== Thread ==>

Subject: Re: USB-to-serial
From: Dirk Zimoch <[email protected]>
To: <[email protected]>
Date: Wed, 20 May 2015 16:43:00 +0200
Hi Eliot

If the USB device would not be recognized or permissions were wrong you would see:
/dev/ttyUSB0 Can't open  No such file or directory
or
/dev/ttyUSB0 Can't open  Permission denied

Since you reported no such error I assume that Linux has successfully recognized the USB device and loaded the driver. Thus running modprobe manually is not necessary and will not help. Also permissions seem to be ok.

If the device is has a RS232 port (what I assume because most PCs have only RS232 serial ports), there should be no pinout problem, because that is standardized. If you did not need a null-modem cable to connect to the serial port of the PC you should not need one for the USB-to-serial either.

However are you sure that the USB-to-serial is RS232 and not maybe RS485? You may be able to find out with lsusb -v (maybe you need to be root to get all information).

Also make sure that serial parameters like baud rate, parity, stop bits, are set correctly.

Hardware handshake may also be an issue. Maybe the device expects it and the USB-to-serial does not have it or the other way round.

Of course the device may simply be broken. Do you have a serial tester like this one? http://www.chipkin.com/rs-232-mini-tester/

How to test quickly:
Connect the USB-to-serial to a USB port of your PC and to the serial port of your PC with a null-modem cable (i.e. crossed serial cable).

Make sure the two ports have the same baud rate:
stty -F /dev/ttyUSB0
stty -F /dev/ttyS0

in one terminal run
cat /dev/ttyS0

in another terminal run
{ echo Hello world; sleep 1; } > /dev/ttyUSB0

If you see the output in the first terminal, then your USB device can send. Also try the other way round to check if it can receive.

Good luck!
Dirk


On 19.05.2015 21:33, Specht, Eliot D. wrote:
​I have a Eurotherm 2416 temperature controller which travels with me. I
was using a desktop computer to run an EPICS IOC, but I realized this
was foolish and am replacing it with a laptop. The desktop has a
built-in serial port, while the laptop uses a USB-to-serial port. I'm
running the same EPICS configuration with some updated modules, but the
serial communications which worked on the desktop do not work on the
laptop. I get errors with "No reply from device".


I'm hoping someone can explain the confusing results of my search of
tech-talk. Some posts suggest that I just plug in the USB-to-serial and
use the /dev/ttyUSB0 device which is automatically created. Others
suggest that I need to use a command like "modprobe ftdi_sio
vendor=0x67b product=0x2303", which gives the error "ftdi_sio: unknown
parameter 'vendor' ".


Question: do I need to use the "modprobe ftdi_sio" command, and if so
why is the 'vendor' parameter giving it trouble?


Details:

Eurotherm 2416 temperature controller with serial interface

base-3.15.1

asyn-4-26

stream-2-6a

sateco Eurotherm protocols from X.L. Wang



References:
USB-to-serial Specht, Eliot D.

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