Random DTR and RTS signal under Windows 7


I have installed the lastest PL2303_Prolific_DriverInstaller_v1.9.0.zip on windows 7 64 bits, and I have some random signal on the DTR and RTS pin.

I use the DTR pin to hard reset my circuit.

Under linux I have no problem, but under Windows I see sometimes DTR and RTS go UP and after 2 seconds go Down.

I’ve desactived all the “USB selective suspends settings” and “Allow the computer to turn off this device to save power” in windows.

On the first joined image, the first measure is the RTS and the second is DTR, with 500ms/div

DTR and RTS 500ms](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1033308/TEK0000.JPG?1394700548)

On the second image, it’s with 10s/div

DTR and RTS 10s](https://d2r1vs3d9006ap.cloudfront.net/s3_images/1033326/TEK0001.JPG?1394702553)

Have you seen the same thing, or have you a solution ?

It not seems to be random but every 32.6s (0x7fff ?) and only RTS and DTR change, not the other pin.

Hello Folg,

First of all, I need to commend you for bringing us such detailed information. I really appreciate what you have done here.

Are you dual-booting your box (meaning, are you using the same machine when you are doing this test)? There are three possible areas we could criticize here:

  1. Windows OS
  2. Hardware
  3. Drivers

The Windows OS could have some hardware or driver related options that could interfere here (I wonder if XP would have the same issue here).

Maybe the hardware or cable is picking up on some secondary hum (this theory sounds good in my head)… but I would like to see if you are using the same machine for your purposes.

We can also try and use older drivers to see if that will take care of the spikes.

Kind regards,
Plugable Technologies

More I test the less I understand :
For my firsts tests, I’ve tested on a Dell laptop with :
Windows 7 Pro x64
Ubuntu 12.04 x64
Windows 7 Pro x64 in virtualbox under Ubuntu.

On Linux it’s OK, on both Windows I’ve the strange signal.

On a desktop computer with Windows 7 Ultimate x64 it’s OK.

I’ve installed a fresh Windows 7 Pro x64 on my virtualbox and it’s OK.

I think the problem must be a software or a driver on my install.


I found the misapplication : it’s Sony PC Companion :
When it’s desactivated, there is no problem,
When I manually search a phone I’ve the problem,

It’s started at boot and seems to search for a phone every 32.6 sec…

Kind regards,

Hi Folg,

Thank you for following up and sharing the solution to this problem! It is strange that a program like this is polling the USB ports every so often, but that explains the regular spikes. I wish we could have a nice oscilloscope like you do because there is no way we could recreate this or analyze the output like you can. That is why I am glad this could be solved by the process of elimination. Thanks again for all your information.

Kind regards,
Plugable Technologies