When testing new RS232 devices, I tend to short RX and TX and then use
But you say that you are experiencing the device vanishing when using it with FreeBSD? There isn't too much I can recommend for that. Perhaps try it in VirtualBox running on FreeBSD and use the USBv1.1 passthrough? Luckily v1.1 won't be the bottleneck in this case.
It is strange that it works with Linux but not FreeBSD. Possibly it could be a power thing but usb / serial adapters specifically do tend to use very little.
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or some code I wrote a while back to see if bytes get through. They all seem to say they use some random Prolific chip but none of them are really the same, often some are dead.But you say that you are experiencing the device vanishing when using it with FreeBSD? There isn't too much I can recommend for that. Perhaps try it in VirtualBox running on FreeBSD and use the USBv1.1 passthrough? Luckily v1.1 won't be the bottleneck in this case.
It is strange that it works with Linux but not FreeBSD. Possibly it could be a power thing but usb / serial adapters specifically do tend to use very little.