Apple Express Fax/Modem - Manual (Page 145)

6 Remote digital loopback test In this mode, characters sent to the
remote modem are echoed back to the local modem exactly as they
were received by the remote modem. This mode tests both local
and remote modems and telephone circuits.
7 Remote digital loopback with self-test Initiates a Remote Digital
Loopback (like &T6) with self-test data pattern generation and
error checking.
8 Local analog loopback with self-test Initiates a Local Analog
Loopback (like &T1) with self-test data pattern generation and
error checking.
The tests terminate when an AT&T0 command is issued or when
register S18 expires. In the self-test mode, an error counter counts the
number of errors and sends the final result to the host at the end of the
test. The maximum number of errors that can be counted is 255.
Note: &T1 takes an optional parameter (a single character, A or O) to indicate
whether the analog loopback must be done in originate (default) or
answer mode.
&U n Trellis coding Enables/disables Trellis code modulation in V.32.
0 Enable Trellis coding.
1 Disable Trellis coding.
&V n Display profiles Displays the following information:
m Active profile
m Stored profile 0
m Stored profile 1
m Stored telephone numbers (see AT&Z).
&W n Profile saving This command saves the current active profile:
0 Saves the active profile into profile 0.
1 Saves the active profile into profile 1.
133 M O D E M C O M M A N D S E T