>As I understand it from the help files for MPLAB, using the "Make"
>option should build only _changed_ files and the "Build" option builds
>_all_ files.
>
>On my setup (using multiple .ASM files and a .LKR file) _all_ files get
>built regardless of which option I use.
>
>I am using version 4.12 of MPLAB.

This usually means that MPLAB can't locate the include files used by your
project. MPLAB then has no way of checking if those files have changed to
know what needs built and what doesn't, so it rebuilds everything, just to
be safe.

On the "Edit Project" dialog, there is an entry for include path and an
entry for linker script path. Make sure that both of these are populated
with the appropriate (';' delimited) path lists. Note that it's quite
possible that the build tools themselves will be able to find the include
files, but MPLAB will not, as the build tools often have additional innate
knowledge of how to find these files. E.g., MPLAB-C17/18 checks the
MCC_INCLUDE environment variable.

Jim