M377-2 MULT BOARD

Nissan ecu daughterboard with 2x 27C256 eprom chips (27C256HGJ85).
ECU jumpers must be soldered to read from daughterboard. Daughterboard jumpers must be soldered to match the ecu they are placed in.
Data is stored ODD/EVEN or SKIP byte order, depends on daughterboard solder configuration. Most popular is U1-ODD-H bytes, U2-EVEN-L bytes. ECU map bin file can be imported to/exported from nistune software.
This is oldschool technology from 90ies when large memory chips where expensive. Two low memory chips were used to lower the costs.

Some of the daughterboards uses encryption to disable the alteration of ROM images. In that case you will need to read all rom data and compare to stock ecu image data files.

More daughterboard manufacturers and models:
PLMS SR20 daughterboards
Nistune
RS-Enthalpy
JWT
Calum Daughterboard (Calumsult)