Topic: Windows Dropps Comm Port using USB to Serial Adapater

By: Tim S

Posted on: Oct 16 2010 at 09:15:13 PM

Hello all.
Occasionally while using the microsoft MSCOM object, the COMM port will go away. It may re-appear and it may not. Can you tell me for certain, if your object will have the same problem. The flavor of windows does not matter, XP, Vista, Win7 - all flavors of each.

Thank you
Tim

By: Support

Posted on: Oct 17 2010 at 12:32:23 AM

An ocx must rely on the windows api and if windows thinks the port has gone then there's not much any ocx can do about it.

From what you're saying it sounds as if the USB cable was physically disconnected. As you know USB doesn't have any locking mechanism to ensure a connector remains connected. It doesn't take much to dislodge a usb plug. Just a fraction of an inch, sometimes just a knock on the cable, is enough to kill the device and even if it reconnects instantly any open port handles are lost.

Consider power saving - actually I don't know but do usb ports have power saving capability? If they do then it's possible that after periods of inactivity the port closes down making Windows think the RS232 port has been disconnected. If that was a possibility then consider using the port every so often to keep it alive. Polling/inputting wouldn't do that unless actual data was received. Inputting just reads the ocx receive buffer. Only sending data or changing the state of one of the control lines would be seen as port activity. If it's possible that power saving is kicking in then try toggling DTR or outputting some data which would be ignored by the other side such as a null or an xon char.

If it's possible that usb ports are being physically disconnected - I've seen that often on laptops where users keep sliding them around the desk and of course when you ask they'll deny all knowledge.

But, to answer your original question honestly - if Windows says the port has been disconnected then any ocx is going to have the same problem so no, our ocx isn't going to fix that problem.

By: Holland

Posted on: Oct 19 2010 at 09:44:17 PM

I have seen this happen with some USB to Serial adapters when the laptop went into power suspend. If you take it out of suspend, it will not restart the USB adapter. I select the ATEN US232A adapter because it's driver could recover from such a power suspend. It also has Windows 2000, XP, VISTA and 7 both 32 and 64 bit drivers.

By: Tim

Posted on: Dec 2 2010 at 05:55:14 AM

All power settings are set to never change (always on). The physical connector is not touched since it is behind a counter out of reach, AND there are a growing number of customers who have the same exact problem, all using Prolific USB to Serial Adapter (driver anyway).

I don't think it is the hardware at all since it happens across many different PC's, some more often than others. In fact these computers have different OS
versions, do not auto update Windoz and happen at totally random times of day.

Any more thoughts? This is a killer problem to have!
Tim

By: Support

Posted on: Dec 2 2010 at 10:49:38 AM

In your first post back in October you said that it was using the MSComm control and you asked if ours would solve the problem.

I said that it depends on what the problem is.

When the port "goes away" I assume you mean that it disappears from Device Manager. If the port is disappearing from device manager then that means that Windows no longer has the port in which case the port has gone and that affect any software using that port no matter what OCX you were using - so, in that case, it's unlikely that our OCX could solve that problem.

However - if you mean that the port just stops working for a while which blocks the software and then sometimes it unblocks and carries on. Then that is a different problem - the port hasn't "Gone away". It's still there, it's just locked up. In that case it is possible that our OCX might solve that problem - assuming that there is no problem in the application software.

Did you actually try with our OCX ?