FT232R COM port issue over time

[Pack34]

On a project I'm using an FT232R to provide simple control and configuration to a project. Everything works fine until its been used for an extensive amount of time (weeks). I end up needing to attempt to connect to the chip repeatedly before it will connect.

I had originally thought that the customer was doing something wrong with the prototype, either the USB cable was loose, windows update issues (tested on XP and 7) or the battery supply for the system was disconnected. However, suddenly the prototype I had in the lab started exhibiting the same issue. The feedback I'm getting in the program's debug is that the access to the COM port is being denied. If I attempt to connect to the system a couple more times it connects fine. I haven't touched the chip using FTDI's configuration program so I'm seeing the TX (to the board) LED go off but not the RX (to the computer). I'm doubting it's a firmware issue on my end because of the error I'm getting in the debug.

I lifted the schematic directly from the datasheet (the same one SparkFun uses) and I'm at a bit of a loss as to why the chip appears to be failing. Since the system uses a switching supply for the 5V rail I decided to have the FTDI chip be powered by the USB and I think that this might be where it's failing.

I'm planning on modifying one of the prototypes to use the board's 5V rail instead of the USB to power the FTDI circuit and leaving the USB's 5V pin floating. This seems like a long shot and I was wondering if anyone else here started seeing the same issue arise on the FT232R since it seems to be a rather common chip.

Thoughts?

[Psi]

When exactly does the problem present itself?
After you have plugged the usb into a freshly booted PC.
Or after it has been removed/reinserted a few times.
Or in the middle of a serial data transfer does it disconnect and give the access denied message?
etc..

Sounds to me like the serial port code/component your using in your program to connect to the port maybe locking up the windows driver preventing it from unmounting/remounting until after a timeout has occurred.

It maybe to do with pulling out the USB cable at the precise time some communication is happening and reinserting too quickly.


Also, how are you locating the com port for the device? Are you scanning all system comports in sequence looking for a responce to your protocol etc..
or asking windows which comport is a USB ft232 chip etc..

[Andreas]

Thoughts?

Perhaps a EMC problem?
Is the PC and the system powered from the same wall outlet?
Eventually series resistors (470R-1K) in the data lines could help.

With best regards

Andreas

[tszaboo]

Thoughts?

Perhaps a EMC problem?
Is the PC and the system powered from the same wall outlet?
Eventually series resistors (470R-1K) in the data lines could help.

With best regards

Andreas

It could be ESD. But that value seems much more I've ever seen on USB, maybe 33-47 ohm. Also, ferrite here and there might help.
But I've seen other strange things from FTDI. Once I saw a plugged in FTDI converter identified as a mouse. And the device was constantly sending data. The mouse on the screen was jumping all over the place opening random applications and rearranging the computer. It really made my day.

[nctnico]

I recommend using the CP2102 from Silabs. I have the same issues with the FT232 which is annoying to say the least. In most cases switching something on/off causes the FT232 to stop working. Grounding everything can help a bit. I didn't try a USB isolator but that could be a solution as well.

[Andreas]

But that value seems much more I've ever seen on USB, maybe 33-47 ohm. Also, ferrite here and there might help.

the 470R-1K are not for the high speed USB data lines. But for the TX and RX line on the other side of the chip.
A ferrite 600-1000 Ohms in the GND line might also help.
I recommend this measures only for BUS powered USB - RS232 devices. For the system powered devices the EMC problem is transferred to the USB side.

with best regards

Andreas

[amyk]

Tried Linux? This can help isolate whether the problem is really hardware or software.

[Jon Chandler]

One problem I have had with USB serial adapters is that they eventually hang if they are sending data to the PC and the PC is ignoring it.  Works find if a terminal window is receiving the data but hangs if the data is just being ignored.