I'm afraid I didn't explain what I was referring to.

I have 3 USB devices that contain micro-controllers/processors. What I'm
trying to do is get them to communicate with my PC via USB. Sometime when I
plug one of the devices in it comes up as
/dev/ttyUSB0
Occasionally as
/dev/ttyUSB1
Occasionally, but rarely as
/dev/ttyUSB2

The comm program I using gtkterm has to be set/changed to match the port
designation Linux decides to call it even though I may be using the same
physical USB hole. In the days of RS232 the physical port set up as COM1
was always called COM1, or something similar, in the software. The software
did not name them dynamically. (I believe the comms could be ASSIGNED other
names but I never used or tried that.)

Anyway, is there a way to have a certain physical USB port be assigned a
specific ttyUSBx?

If not how can I get gtkterm find the port designation and change to it?

I have tried Minicom and Cutecom. Minicom did communicate after a few
minutes of setup but then for some reason, probably something I did,
decided not to work. A new install has not corrected this. Cutecom, it
seems like it is connected all the time. Characters typed are returned even
without the device on the other end Tx and Rx pins not strapped for
loop-back and echo is supposedly turned off.

I'm also open for trying another comm program.