difference between cu and putty for serial connections

[Talayeh Asadi]

hi all,

i'm trying to activate my custom boot0 on a headless server. i got my
required results while connecting by cu, but not when i use putty to
connect..

here's the scenario:
one of my goals in this custom boot0 is to deactivate all keys but F2 for
some reasons..
i applied required changes to the boot0.S code and applied DONLY_F_KEYS in
the Makefile and changed the flags BOOT_BOOT0_FLAGS to required values and
got required output using cu.

but when i connect to the mentioned server using putty, my F keys don't
work and i  have to remove DONLY_F_KEYS in Makefile so '2' Key become
available (SIO mode activated??)

i don't know so much things about this sio mode here.. would someone please
explain  their difference to me? i have no idea.. is it related to the
keymap differences?

any suggestions are really appritiated.. Thank you all  :)

Best Regards,
t.a.k