The once popular Kermit program. that helped transfer files from machine to machine by serial lines, was also implemnted on UCSD p_systems.
Here a collection of sources for various systems and versions of UCSD p-System
Apple II
IBM PC
Magiscan 2
Pecan Version IV.x UCSD p-System
Terak
Western Digital Pascal Microengine
A manual for UCSD p-system Kermit is not found, this manual of ckermit may help because Kermit is quite standardized.