Telebit T3000 Reference Manual page 123

When S51 is set to 252, the modem examines each
AT prefix to derive the current interface speed, and
you cannot enter a new command line until the result
code from the previous command is displayed. Ifno
command lines have been entered after powering on,
the speed at which the default configuration was
saved is the speed the modem uses to send RING and
CONNECT messages when it receives an incoming
call.
When S51 is set to 253, 254, or 255, the modem
checks the interface speed on the first AT prefix only
after one of the following events occur:
• The modem is powered on or reset.
• S51 is set to 253, 254, or 255 while in
command mode.
• A data call disconnects and the modem goes
on-hook.
• A break is received.
• A NO CARRIER condition is generated
because connect time has expired (S7 register),
dial command is aborted, or the carrier is lost.
Since the interface speed is not checked after each
command line, you can enter multiple command
lines without waiting for the results from the
previous command. This may be useful for
communications software scripting.
If no command lines have been entered after
powering on, themodem uses 38,400bps (S51=253),
19,200 bps (S51=254), or 9,600 bps (S51=255) to
send RING and CONNECT messages when the
modem receives a call.
6-16 AT Register Descriptions