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Author Topic: FT4232H causing communication problems on another device  (Read 874 times)


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FT4232H causing communication problems on another device
« on: March 16, 2021, 10:16:12 AM »

Hello there,

First post. I am not really sure if this post should go into the drivers section or hardware/software section, anyway:

At the moment I am making use of FT4232H FTDI device to be able use up to 4 RS232/485 COM ports from a given USB. Currently the O.S. I am using is a custom Linux distribution with kernel 4.14.92 .
After much debugging and testing I have discovered that, whenever I make use of one of the four COM interfaces that the device creates , particularly COM2, another device communications are interrupting and stops communicating from that moment . This is weird for me as this device, which is a ST60 2230-PU Wifi+ Bluetooth device, is connected on another USB bus on the same HUB . Hub model is  USB5807. For more details, Wifi+Bluetooth device is connected to downstream P5 and the FT4232H is connected to the downstream P7 of this HUB. 
I attach a image of my setup for clarification purposes.

Whenever I use any of the other 3 COM interfaces created by the FTDI I find no compatibility issues. I have some doubts regarding what may be happening:

- Could there be any difference in the behavior of the 4 ports (COM1 to COM4 ) regarding USB communications ? 
- What can be producing USB communication issues in the other USB bus?
- Is there anything we may have not considered in the hardware design regarding FTDI ?

I already contacted the Wifi+ Bluetooth manufacturer and they are not aware of problems like this one.

Thank you very much! Any help will be appreciated!

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Re: FT4232H causing communication problems on another device
« Reply #1 on: March 18, 2021, 04:32:35 PM »


This is not a known issue with our product with our Linux drivers and the IC and driver is widely used.

There is no difference in the behaviour of the 4 ports (COM1 to COM4 ) regarding USB communications.

The nature of USB communication has to be taken into account.
The communication with USB devices depends on multiple factors such as other USB devices on the bus, USB Host scheduling, USB latency, OS processing, etc.

You attached your setup. Is this all inclusive on custom hardware or are the elements separate?

Is your COM2 operating much differently from the other COM Ports? For example, is there more traffic?
What is each of the FT4232H ports connected to externally and what is the expected throughput of each?
Are you using flow control on all the FT4232H ports?

Could there be issues with the Linux board running out of CPU resources to access more than one device concurrently?

You could perform tests with our known good hardware and maybe connect that to a different Linux system to see what the results are like:

FT4232H-56 Mini-Module
FT4232H Mini-Module

The FT-MOD-4232HUB might be useful as the ST60 2230-PU Wifi+ Bluetooth device can be connected to one of the ports.

Can you also test with our D2XX Drivers (rather than VCP drivers) to see if the results are the same? See the Linux Driver Installation Guide and D2XX Programmer’s Guide for more information.

Maybe there are other FTDI Community users who can help you further.

Best Regards,
FTDI Community