Epson GT-6500 EN - Manual (Page 85)

Function Level and Commands
Each function level builds on the previous level, so all commands and
parameters in previous levels are included in higher levels. Extended
commands are available regardless of function level.
Using the function level
Higher function levels include all the commands of lower function
levels. Your programs should always check the function level of the
connected scanner and should send only those commands available on
that level.
Note:
All settings have initial default values, and some models have settings
that can be set using DIP switches or the control panel. However,
settings made using commands take precedence over these other
setting methods; to avoid errors and confusion, it is recommended you
make necessary settings using commands whenever possible.
Command Usage 2-47