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Chapter 5 - Testing the Modem
5.3 Digital Loopback Test/V.54 Loop 2(Remote/Automatic)In this test, your modem must be On-line with another modem set up to
respond to a request for Digital Loopback. The test is as follows:
1. Enter Terminal mode.Type AT and hit ENTER. An OK message
displays.
2. Dial the remote modem by entering the Dial command and the phone
number, to establish On-line mode.
Note: Set the &T4 command on the remote modem prior to running test.
3. Type the Escape Sequence (+++AT<CR> or <BREAK>AT<CR>) to
enter Command mode, maintaining the remote modem connection.
4. Type ATU2 and hit ENTER. The local modem transmits an
unscrambled marking signal. The remote modem enters Digital
Loopback mode. The local modem exits Command mode and enters
pseudo On-line mode.
5. Type multiple uppercase "U" characters to send an alternating test
pattern of ones and zeros. The data received by the remote modem
enters the analog receiver and is converted to digital data. The data is
reconverted into analog, then looped through the transmitter back to the
local modem. If the data entered from the keyboard is the same as the
data received on the monitor, the modem has passed the test.
Figure 5-3. Digital Loopback Test (remote / automatic)
Digital Analog Analog Digital
Computer or Terminal Computer or Terminal
Local Modem Remote Modem
UUUU