Hello Bert,

SDCC is a free C Compiler and more stuff for uC like 8051.
http://sdcc.sourceforge.net/links.html

I don't think SDCC can generate object file in INTEL OMF-51 format. It is a little surprise because 8051 is an INTEL uC, but I could be wrong.

There may be a free/open source C compiler which can generate object files in OMF-51. Hope to hear what experts say about it.

Thanks,

Joseph