Not all functions under CP/M 3.x are compatible to those of CP/M 2.2.
Particularly direct BIOS calls may cause crashing CP/M 3.x.
Also the BDOS function 27 — Return address of allocation map — may cause incorrect results.
(User of TURBO-PASCAL 3.x know the problems determining the free disc space.)
Use this RSX if you are running programs making problems as described above.
After installing the RSX CP/M 3.x acts like CP/M 2.2.
Here the source files: