FTDI USB to Serial converter chip

[mwhatley]

Excuse the slightly off topic question but ... Has anyone used any of these chips? I'm working on a 18F2321 project that uses this chip. The project works fine but my problem is on the PC that we were going to use to test the finished board. The FTDI part sets up a virtural comm port when connected to the PC's USB port. The problem is that each time a new board is connected it creates a COMXX where XX is the the last comm port number plus one. I'm up to COM82 after testing a few boards (It started with COM3). The test program on the PC is a VB6 routine and VB6 only allows up to COM16. I have seen this same thing on commerical USB-Serial products. I know I can go into the device manager and change the comm numbers but that sure makes testing the board a lot harder. Anyone encountered this? Is there a way to make the Windows/FTDI start at COM3 each time? Anyone have any suggestions?
Thanks,
Mark

[keithdoxey]

Hi Mark,

Not sure if this reply will help or not !!!!

I have had "similar" problems with other USB converters. I have several converters using different chipsets and I have discovered the following.

1. When first installed Windows will allocate a COM port. eg "3"

2. If that SAME device is plugged into the SAME PC on a DIFFERENT USB Port, Windows will allocate a DIFFERENT COM Port. eg "4"

3. Another adapter using the same chipset eg Prolific, can be inserted into the first USB port and will be treated as COM 3 but if a different brand is inserted it will become COM 5

4. As you correctly point out, you can use Device Mangler to change the port number but what you cant do is uninstall an existing adapter if it isnt plugged in because it doesnt exist even though it is assigned resources.

Now the reason why this might not help......

I have a couple of the FTDI MM232R converters but havent got round to using them yet, to be honest I cant find the bloody things!!!! was looking the other night

Looking at the datasheet I see the following sentance.....
Device supplied pre-programmed with a unique USB serial number

I wonder if this is causing Windows to see each of your boards as a "new" device so giving each board a different COM port.

If your FTDI chip is basically the same as the ones in the MM232R and you dont use the serial number for anything perhaps trying to overwrite it with identical numbers may cure the problem.

The way USB Plug and Pray had been implemented is a nightmare. Why can things like Cameras and Scanners be plugged into any USB port or hub but USB Com Ports need you to remember exactly which front/rear socket you used and which outlet on which hub. GGGGGRRRRRRRRRRRRRRRRR!!!!!!!

[dhouston]

If you are using MSCOMM32.OCX you are limited to COM10. If you use the CreateFile method you can use up to COM256 but have to use a different syntax for ports above COM16. I can dig up the details if you need them. I've also seen a patch for MSCOMM32.OCX to allow all 256 ports but am leary of it.

[dhouston]

With CreateFile use "\\.\" before "COMnn" e.g. "\\.\COM99"

To modify MSCOMM32.OCX, Google using "MSCOMM32.OCX 3D 10 00".

You might also ask FTDI Support for suggestions.

[JElliott]

I also have had similiar issues with the FTDI devices. I definately know if you change the serial number of the device it will open a new comport. I don't have a solution for this but after much web searching I did find a solution for reclaiming these ports. I have enclosed PDF of the web page that provides the directions. Helps ease the pain

Regards,

Jeff E.

[tenaja]

If you are up to 82, and you aren't using it for an open free-for-all com port, then you really should get your own PID's from FTDI. You should also be using the d2xx drivers, and eliminate the vcp's all together.

Doing this will place your device in the USB controllers list of Device Mgr, and not in the Port list. Not only that, by getting your free PID number, it will make your product look a little more custom, and will remove all the hassles of selecting the proper COM port in the program.

All of this is covered in the data sheets. It is worth the effort to learn, because it makes your product more professional looking and much more user friendly--especially if someone randomly happens to have an FTDI serial converter cable plugged into their computer.

[tenaja]

By the way, there are d2xx communications code samples for using the DLL's on the ftdi web site, too. They show how to use the chip without a COMx assigned at all.