Michael Graff <explorer@flame.org> writes:

> The Keyspan ones use a small microcontroller.  I'd _really_ like to
> hack together a special firmware which will let me have more than one
> output as a transmit line.

Yep, the Cypress (formery Anchor) EZ-USB.

You might be interested in "Hacking the Keyspan USB Serial Adaptor",
http://www.omnigroup.com/~wiml/soft/pic/keyspan.html

        - Nathan