PL/M was created by Gary Kildall as an adaptation of PL/I. He used it to write CP/M for the 8080, and later sold the compiler to Intel. So I'm guessing Intel PL/M-51 was simply a derivative of the original. Intel doesn't appear to sell it anymore. Just from the examples I've read in various places, it appeared to be a useful little language. I've read that it was somewhat difficult to write a compiler for.


As for your idea of adapting CP/M as an MCS-51 RTOS... Was CP/M placed in the public domain, copylefted, or otherwise released for derivative use? I know there's some archives, but I don't know what restrictions have been placed on it's use.


See: http://www.cpm.z80.de/source.html


There's appears to be a PL/M-80 compiler source there too.