Epson PX4 info page

Picture of a PX4
Pinouts and circuit diagrams:

Also i have summarised the PX4 manual with this CP/M command reference.

Extra Info:
A bunch of useful programs for use on and with the px4 can be found here such as EPROM images for the utilities, a cp/m emulator, filink file transfer tools, and assorted other utils.

If you don't find what you are looking for here, try this PX-4 Document Archive.