COM port number too high

[kranenborg]

Hello,

I have a perfectly running ZBASIC system using Elba's ZBASIC USB-TTL converter. The COM port number is now very high (33) due to the fact that I had to use MPROG many times to arrive at the proper settings for the converter regarding inverted/non-inverted signal settings.

Like said this does not pose any problem for the ZBASIC configuration itself, but many other support programs that I want to use (for example PLX-DAQ from Parallax for downloading results from the active serial port directly into MS-Excel) only support selection of COM port numbers up to number 15. Therefore I would like to do a reinstall of the converter such that I get a much lower port number. Is there a way to do that? Do I need to remove the port driver in Windows XP while I have the converter plugged in? Do I need to change something in the EEPROM settings of the converter's FT232R chip? (Note that there is not the issue of inactive but still present COM ports in the range of 10-32, they are simply not there but still some mechanism increases the new port number after each application of MPROG)

Thanks,
Jurjen

[dkinzer]

I would like to do a reinstall of the converter such that I get a much lower port number. Is there a way to do that?

You can remove all FTDI devices from your system using FTDI's FTClean Utility. After running that utility, plugging in an FTDI USB device will require installing the drivers again and the COM numbers will be much lower.

An alternate method is to change the COM port assigned to the particular device you're using (as described in the USB-TTL Reference Manual). You can choose a lower numbered one that is marked "in use" and then force it to use that port number. You do have to be careful, however, to avoid re-using a COM port that is assigned to another device that you intend to use in the future.

I usually find it simpler to just use FTClean.

[kranenborg]

Hello Don,

Thanks for the quick response. I have used the quick-and-dirty forced port number approach which works out well. At some point I will though use FTClean since to my surprise all ports below number 33 were marked as in-use

Regards,
Jurjen

[GTBecker]

FWIW, on the 16-port limit, a fix that allows 255 ports on many
applications exists.

If the application uses it, overwriting system file
...\System32\MSCOMM32.OCX with a modified version will permit 255
ports. A modified MSCOMM32.OCX is in a folder in
http://rightime.com/LF/DBR_Control.zip .

[dkinzer]

[T]o my surprise all ports below number 33 were marked as in-use

That just means that the association was made at some time between each of those COM ports and some device. That doesn't mean that all of those devices are actually in use at the moment.

For example, if you have two FTDI-based USB devices, when you plug them in and install the drivers, Windows will assign the next two COM ports to them. If you then unplug those USB devices and plug in a different FTDI-based device, install the drivers, and then go look at the device properties, you'll see the the COM ports for the first two FTDI-based USB devices are marked as "in use" even though they're not currently plugged in.

I believe that Windows associates the COM port number with the USB device serial number and that association remains (irrespective of whether the device is actually plugged in) until you manually delete the device.

[stevech]

I think it's common knowledge that in Windows' Device Manager's View->show hidden devices, unplugged USB things are listed. So perhaps under Ports, you can delete prior USB to serial thingies and next time you plug that item in, it can get a new COM port number.

And to change the COM port number for a USB or hardware UART device, you can use the properties and advanced settings choice.