Multi-Tech Systems MT3334HD8 - Manual (Page 49)

3 AT Commands
CommPlete Communications Server 43
Un Loopback Test Modes
n = 0–3
Default: None
Loopback tests send data through the modem in such a way that it loops back to the terminal where it was
entered, testing all the circuits along the way. The U command selects from several loopback tests. See
Chapter 5, “Testing the MT3334HD8,” for more information.
ATU0 places the modem in originate mode for the local analog loopback test.
ATU1 places the modem in answer mode for the local analog loopback test.
ATU2 performs the remote digital loopback test.
ATU3 performs the local digital loopback test.