HP Fortran Programmer's Guide (March 2010)

Compiling and linking
Compiling with the f90 command
Chapter 280
NOTE The compiler generates a .mod file for each file that defines a Fortran module.
It also reads the .mod files when compiling source files that use modules. Do
not specify .mod files on the command line. If you do, the compiler will pass
them to the linker, which will try (and fail) to link them into the executable. For
more information about .mod files, see “Compiling programs with modules” on
page 88.