Toshiba V.90 - Manual (Page 40)

AT Commands
AT command formats
21
Result Codes:
Nn Modulation handshake
This command controls whether or not the local modem performs
a negotiated handshake at connection time with the remote
modem when the communication speed of the two modems is
different.
Result Codes:
On Return online to data mode
M2 The speaker is always on when modem is off-hook.
OK n=0,1,2
ERROR Otherwise
N0 When originating or answering, this is for handshake
only at the communication standard specified by S37 and
the ATB command.
N1 When originating or answering, begin the handshake at
the communication standard specified by S37 and the
ATB command (default).
During handshake, a lower transmission speed may be
selected.
OK n=0,1
ERROR Otherwise
O0 Instructs the modem to exit online command mode and return
to data mode (see AT escape sequence, +++).
O1 This command issues a retrain before returning to online data
mode.