It only takes 4 bits for all the controls. I have the mode selection implemented in switches. It was necessary to add buffers between the parallel port and the PIC inputs. Communications Quarterly for full info. FAR Circuits has the boards.
Article gives parts list, adjustment and applications info.
I hastily added a page of notes at the front of the source listing to orient the reader. Without the hardware description and schematic it's only likely to be of casual interest to anyone but a fairly hardcore PIC user. They have fixed a number of bugs and have modified many of the subroutines to make them more efficient and easier to understand. Most of all, they documented the code thoroughly. Subroutines now have headers with inputs and outputs listed.