Hexam is a machine code editor, assembler and monitor in a "cartridge" that fits in the expansion port, made by ACE Software.
For the monitor, |MON and for the editor, |EDT .
The E.ROM is on bank 2.
The C.ROM is on bank 8.
Now, thanks to Jose Leandro, the hardware specialist of the spectrum, with his famous page :
We can know more about this hardware.