[BALU] Query regarding comm ports in windows

Thomas Stover thomas at wsinnovations.com
Tue Dec 16 16:22:37 CST 2008

I've dealt with this issue at length. There might be a way to do it, but 
in my experience no. In fact I have had examples like this:

-2 usb-serial cables attached swap com ports after every reboot
-unplugging and replugging usb-serial cables assigns the cable 
continually incrementing com ports
-plugging the cable in different usb ports give all sorts of different 
-no constancy across version of 'doz

Some cables have drivers that let you go in and assign a port - but they 
still don't always work in my experience.

btw We have had terrible luck in buying cables that work at all. We even 
have a box behind me on the shelf with 50+ cables that send data, but 
wont receive it! (on those I have even taken them apart to make sure the 
leads were connected).

Serial cards, as Hiram suggest, are more expensive, but typically get 
the job done right the first time. Of course for laptops and PC104 
systems that gets even more pricey.

Hiram Lester wrote:
> I can't speak to the ability to do this programmatically, but from the couple of times I have used such adapters, I have observed the same behavior of the COM port number changing from one time/port to another. Are cheap serial cards an option or do these machines actually have the com port header on the motherboard and just not exposed to the outside world?
>>>> <andrew at asi-web.com> 12/16/2008 3:35 PM >>>
> I've got a small problem relating to windows-side comm ports, and I'm  
> hoping some of the windows-afflicted on the list might be able to help  
> me figure it out.
> I've got a program written in Delphi (think Visual Pascal) which  
> requires a serial connection to download information off of a handheld  
> unit.  Some of the people who will be using the unit are using systems  
> which don't have serial ports, so I was asked to test a serial to usb  
> adaptor cable alongside working on the program.
> The serial/usb cable works nicely, but it's causing a problem for me.   
> Because there are third-party uploader/downloader programs being  
> invoked, I have to be able to specify which serial port I'm using to  
> download from the handheld unit.  But the user has also requested that  
> the cable needs to be shiftable - that is, that they can swap it from  
> one USB port to another without having problems running the program.   
> And this particular cable seems to swap out comm ports when swapped  
> between USB slots.  (That may be inherent in the way usb ports work -  
> I don't know enough about them to tell.)
> I can, manually, go investigate the device manager and see which port  
> is being assigned to the cable.  Is there some way to duplicate that  
> effect in code from behind the scenes, and what would be the best way  
> to go about doing that?
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