hexl

This package implements a major mode for editing binary files.  It uses
a program called hexl, supplied with the GNU Emacs distribution, that
can filter a binary into an editable format or from the format back into
binary.  For full instructions, invoke `hexl-mode' on an empty buffer and
do M-x `describe-mode'.

NOTE: Remember to change `hexl-program' or `hexl-options' if needed.

Currently hexl only supports big endian hex output with 16 bit
grouping.

-iso in `hexl-options' will allow iso characters to display in the
ASCII region of the screen (if your Emacs supports this) instead of
changing them to dots.