[NTLK] NCU and serial connection at 230k and 115k

I have always read about the fast serial connection so I wanted to give
it a try.
I downloaded and installed the Serial Enabler Control Panel (v 1.0.3),
the Ser230400 extension and the Ser115200 extension as well. I have 0S
X 10.3.9 with Classic, the USA-28X Keyspan Serial Adapter (say, I use
port 1) and a 2100 with SER-001.

The summary is that, if I choose "Serial 115200" on the Dock and I lock
the Serial Enabler to 115200, NCU connects and transfer stuff rather
quickly (though some rough measurements give me a figure around 78k).
On the other hand there is no way to make the 230k connection work with
NCU: if I set the Serial Enabler at 230400, I can not establish the
connection with the Newton (where of course I am using the "Serial
230400" extension).
I have read that I should set the speed in the "Keyspan USA28X Serial
Assistant" Control Panel but the Advanced button simply doesn't do
anything. Also the "Keyspan Serial Assistant" under OS X doesn't look
like being so helpful in terms of setting a 230k speed.

Given that occasionally some success has been reported on this list for
the 230k connection with NCU (but I could not trace the useful and
practical details of the story):
- Is there something I am missing? Or is NCU (or the USA-28X) limited
to 115k? I read somewhere about a possible limitation to 115k for the
previous USA-28 model.
- Is it normal that the Advanced button of the Keyspan Assistant in
emulated Classic doesn't do anything but "click"? If that is the case,
where can I set the 230k speed in order to make it work with NCU?

Thanks,

Giulio

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