Funnily enough, I did the exact same thing last night and had the exact same problem

- Newton 2100

- Prolific PL2303 chipset based USB ---> serial adapter

- Mac serial cable with DB25 connector on end (I don't think I've ever come across the mac serial to DB9 connector)

- DB25 female to DB9 female adapter

- NCX set up and running on G4 Cube (OS X 10.4.11)

Tried a couple of different drivers; all detected the adapter with no hassles as did NCX. Did the same thing as you - different serial speeds, hard reset, but no connection could ever be found.

I'm assuming the pinout has perhaps changed when you couple the Mac serial cable with the adapter; I could try making my own adapter or find a mac serial --> DB9 cable.

In the end, I fired up my Powerbook 2400c and NCU. I'd had problems with downloading Newton .pkg files under OS X and finding their resource forks damaged when copied to the OS 9-based Powerbook. Ended up finding a small utility that fixed the forks, so at least I was finally able to copy over some of the apps I had saved.

So any thoughts on our plight would be appreciated

JB