3Com Courier Reference page 167

Command Function
&T1
&T2
&T3
&T4
&T5
&T6
&T7
&T8
&T9
&Wn Write the current settings to NVRAM.
&Xn External modems only: Designate the source of synchronous
transmit clock timing signals.
&X0
&X1
&X2
&Yn Break handling. This command lets you send a break to stop
data transfer without disconnecting.
&Y0
&Y1
&Y2
&Y3
If the call is under MNP5 data compression, destructive breaks cause both
modems to reset their data compression tables. When transmission
Ampersand (&) Command Set
Local digital loopback
Local analogue loopback
Not used (error)
Grant Remote Digital Loopback request
Deny Remote Digital Loopback request
Request Remote Digital Loopback
Not used (error)
Local digital loopback with test pattern
Local analogue loopback with test pattern
The Courier V.Everything modem sends transmit
clock timing signals to the DTE over the serial
interface. DTE rate follows the connection rate.
The DTE sends transmit clock timing signals to the
modem over the serial interface. Typical use:
multiplexed leased lines.
The Courier V.Everything modem sends receiver
clock timing signals, which are looped to the
transmit clock and sent to the DTE over the serial
interface. Typical Use: Systems that require
synchronisation of data flowing in both directions.
Destructive, don't send break.
Destructive, expedited.
Nondestructive, expedited.
Nondestructive, unexpedited; the modem sends a
break-in-sequence with data received from your
computer or terminal.
B-11