Start by going to the Device Manager. Once there do the following:Expand the Ports ‘(COM& LPT)’You should be looking at something like this:As you can see Windows has set the port to COM10. However many legacy applications expect the port to be between 1-4. Let’s change that:Right click on the device and click on ‘Properties’.Click on ‘Port Settings’.

The host computer requires serial port drivers (otherwise known as “Virtual. Sections describe Mac OSX and Android installation instructions. Not sure about OSX but on other systems you can monitor the serial port by going to Tools-Serial Port Monitor in the Arduino IDE – Moog Sep 4 '12 at 9:04 Consider changing the title of this question to something that reflects the selected answer.

Then click on ‘Advanced’.Once you’re in ‘Advanced Settings for COM10’ on the bottom you can see the ‘COM Port Number: COM10’. Click on that to change it to the lowest possible number (between 1-4).Then click ‘OK’ on all open Property Windows.Now the device should look like this. I found a code that allows you to remove old associations to COM Ports. You can then plug your adapter in and then associate it with the COM Port you need.1. Start, All Programs, Accessories, Right-click “Command Prompt” in Accessories and choose “Run as Administrator”2. Enter “set devmgrshownonpresentdevices=1″ – without the quotes obviously3. Enter “start devmgmt.msc”4.

In the box that opens, select “Show hidden devices” in the ‘view’ menu.Now if you expand the section on COM ports, all the COM ports that have everbeen created will be displayed, the non present ones being in grey. You canuninstall away anything that you don’t want (right click, select uninstall). I also have the problem where the Prolific USB to serial is installed on com11 and the “advanced” button leads to anohter screen, but there is no provision for changing com port there. Might be IT department blocks that on company PC. I blame the device driver installation software -it SHOULD show defaults and ASK the user if they want to make changes before installing. No nothings can just push the button to install defaults, those of use who know what settings we need could then get it right.Brad Fluharty. Hi Bernie – I’m not sure if your postings on this topic has closed.I had an “Ham” HF radio connected to a desktop XP and a logging program via RS-232.

As I changed bands on the radio, the log program would follow, recording time and date and the frequency of operation. Then, the PC was struck by lightning and I got another PC with new motherboard running Windows 7.I now have a radio that runs a USB cable that controls a Contest Logging program However when using an RS232 cable to control my normal logging for contacts, the program does not see the radio or the cable.I have tried changing the port numbers but the program still does not see the radio. The two existing ports are 1 and 3 both with Nuvoton Drivers.

I tried deleting them but then can not create a new COM1. With the drivers back into the PC, I tried using COM3 for the Ham Logging program but there is still no ‘comms’ between the radio and PC.Please HELP!!Ham/Sam.Jeanie.

Hi JeanieI’m a complete computer illiterate!! Still not sorted yet. I used to run Swisslog with my TS-2000S using a serial cable. A few months ago, I acquired a TS-590S after selling the TS-2000., I entered a small contest and had N1MM installed using a USB cable.

The RS-232 port was used to control the Experk 1K-FA linear. During the contest, N1MM and the linear worked fine.After the contest, I tried running SwissLog but the program could not see the COM port. Reading user comments that N1MM and any logging program can not run together, I removed N1MM although they were on different COM ports Now, I keep getting a message that the Com port I am setting up for Swisslog is being used by another device although there are no other devices connected to the PC. I’ve tried changing the Start and Stop bits and tried various combinations and getting more frustrated!I trust that your dad will have better luckRegardsSam.Richard.

Hi, I am trying to connect a UT61B multimeter to my dell laptop win7 home via a usb to serial cable. They do not specify one.The meter comes with a female 9 pin connector which works fine when connected to an older WXP desktop unit with traditional com ports. I borrowed a Prolific (green) cable to try it on the Dell laptop; loaded the software and can see the cable identified in the Device Manager; set the com port to 1 as required by the meter, but no data is transferred from the meter.The local computer shop says that the BIOS needs to be set up for the USB ports to be seen as COM ports, but the Dell BIOS has nothing that appears to affect this. I believe it’s a hardware problem, maybe a bad green cable. Any comments?.David Roberts. Thanks for posting your question.

There should be no need to set up COM ports in the BIOS for USB serial. Windows does this in software. We have sometimes seen difficulties with multimeters that expected higher voltages for RS-232 than with our serial that uses the Prolific chip. The chip itself only provides TTL logic outputs, and then a serial interface chip takes those outputs and changes them to RS-232, with +7 volts for a one and -7 volts for a zero. The RS-232 standard allows up to +/-15 volts, and some multimeters appear ot require more than the +/-7 volts our chip supplies.

Also, you didn’t mention if your adapter was from Plugable. We don’t supply any green cables. Some devices that claim Prolific chips actually have clones that won’t work with the latest Prolific drivers. If you have a Plugable device, please contact us at, and we can help.

Thanks!.Paul Aeberli. Hello,I want to ask about COM ports when there are multiple users on a PC.We use a piece of document tracking software at work which has barcode scanners attached by USB to each machine.The software has to be configured to look on a specific port for the scanner, which is a global setting for the PC.However, when someone different logs on to the PC, Windows 7 assigns a different COM port number to the scanner for that person (presumably the first available) and this does not always match the COM which has been set up in the software, so needs to be reconfigured each time. The scanners don’t usually get unplugged.Is there a way to fix the COM port for a specific device so it never gets changed, regardless of who is logged in?This would save us considerable effort if these is a way.ThanksDicegirly.David Roberts. Hi, I am using a device which requires COM1. I made this change successfully some while ago but I want to understand what I did and why I did it. The COM port setting in Windows is an arbitrary number that points to a particular address in the computer’s memory where data that is sent back and forth over a serial connection.

If that number has not already been put into use to support a serial device, Windows will let you assign it to any serial device you have currently connected to the computer, such as Plugable’s serial adapter. Since the Port number is assigned by Windows when you connect a serial port, and released when you disconnect it, there would be no advantage in setting all ports to COM1. If two ports were set to COM1 and in use at the same time, this would cause problems, because one serial device would overwrite the information from the other in memory. However, this shouldn’t happen because Windows will not let you assign a COM port to more than one device at a time.The COM ports are arbitrarily assigned by Windows. They are not set with any purpose, so feel free to change to any open COM port when necessary. Some serial communications software will only work with a specified COM port or only with COM1 through COM4.

In those cases, you have to select an appropriate port in the Port Settings window.The numbers range from 1 to 256 in modern Windows versions to allow a large number of serial devices to be attached without causing problems. Modern computers have plenty of memory available, so there is no problem of setting aside enough memory to support 256 ports. The number 256 is selected because it represents the maximum number of ports that can be addressed with one byte (eight bits) of information.When you plug in a device known to Windows, it automatically loads the driver for it. When you unplug that device, Windows automatically unloads the driver. Devices that are similar to each other can use the same driver, and Windows just copies in into memory to be used to control a particular device on a particular COM port.When using USB serial devices, Windows tends to assign the same COM port number to devices plugged into the same USB port. That may be why you are frequently seeing COM10.I hope this helps.DavidPlugable Support.

Windows checks the USB Vendor ID(VID), Product ID (PID) and device serial number each time a USB-Serial device is plugged in, and assigns the next unoccupied COM port if it has not seen that combination of VID, PID, and serial number before. Also, if another serial device is set to use the COM port usually assigned to the Plugable adapter, a new port will be assigned to the PLugable adapter since its previous port is no longer available. There is no setting in Windows that will prevent this behavior.

If you only use one Plugable USB-Serial adapter on this computer, it is possible to set the registry so that Windows ignores the serial number of the adapter, and thereby assigns the same port to any Plugable adapter that is plugged in, but if you are using multiple Plugable adapters, this will make the situation worse. If you would like more information, please contact us directly at with some details about your setup, such as how many serial devices are connected, and how many Plugable devices are being used, and we can give more specific information.Ben. Hi Patryk,Thanks for asking! The COM port section in the device manager is only available when a Serial Port is detected on the system. This can be a built-in serial port, PCI or PCIe serial card, or a USB Serial Adapter like our Plugable PL2303-DB9 USB to DB9 RS232 Serial Adapter ( ). Without one of these physical serial ports the computer will not display the “Ports (COM or LPT)” section in the device manager.If you have any additional questions, please feel free to email our support team directly at “support@plugable.com”, we are happy to help!Pat.Mitchell. Dear Bernie,Thank you for your article.

It was very informative. I have a slightly off topic-question.I am writing some software that needs to know what COM ports are actually available/connected on a Windows machine i.e. It needs to know where to communicate before doing so.Can you suggest a means to determine this? (Think high level stuff like ‘open file COM1:’ and return a value for success or fail).

Yes, I know its odd but the language is new to me and I am unsure if I can even do BIOS calls from it.Any help would be appreciated.Pat.

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