Wed May 30 17:39:07 EDT 2012
Reading the 18F2550 datasheet, here's something I missed:
126.96.36.199 Internal Regulator
The PIC18FX455/X550 devices have a built-in 3.3V reg- ulator to
provide power to the internal transceiver and provide a source for
the internal/external pull-ups. An external 220 nF (±20%) capacitor
is required for stability.
I found it looking up "VREGEN" from inspecting the configuration bits
EDIT: Adding the 220nF did the trick.
Another one for later:
The data in the USB Status register is valid only when the TRNIF
interrupt flag is asserted.