My Prolific Technology, Inc. PL2303 Serial Port adapter doesn't work in either ubuntu 13:10 or 14:04

Question

I have a USB to Serial port adaptor, Prolific Technology, Inc. PL2303 Serial Port which works on ubuntu 10.04, and win xp, win7 machines. However, I have problems with it on Ubuntu 13.10 and 14.04 LTS. It enumerates OK and shows up as /dev/ttyUSB0 or /dev/ttyUSB1. Currently I am trying to connect to a cheap RS232 multimeter which connects to pin 2 (Rx data) and the pin 4 (DTR) line.

1.)Does anybody know whether the usb-serial drivers for PL2303 work or are broken? If they are OK, then 2.)does anyone know how to set or reset the DTR line? This is used to enable or suppress the output from the multimeter.

currently using tcl/tk for accessing hardware.

Answer 1

To answer my own questions:

1. the usb-serial drivers for PL2303 do work and are not broken. I think most of the problems arise from the initialization where the DTR line defaults to -ve volts ie 0. Previous versions of Ubuntu (i.e. 10.04) the default was +ve volts on the DTR line. Note that other usb to serial converters such as Belkin F5U409 in UBUNTU 14.04 default to +ve volts on DTR line thus work OK. Confirmation of working drivers was done using GTKterm and toggling the DTR line. Furthermore connection to a Stanford Research SR830 Lock-in amplifier was established and its identify verified.

2. Having established working drivers, the solution in tcl/tk is to use the -ttycontrol switch within the fconfigure command. i.e.:

   ...
   
   set device "/dev/ttyUSB0"
   
   set dh [open $device r+]
   
   fconfigure $dh -mode $baud_rate,$parity,$data_bits,$stop_bits -translation binary -encoding binary -blocking 0 -buffering line -ttycontrol {RTS 0 DTR 1}
   
   set tmpstr [ read $dh ]
   
   close $dh 
   
   ...
   

Works for me :).