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U-90E Data/Fax Modem
13.2 Loopback Tests
The Analog Loopback Test, Local Digital Loopback Test, Remote Digital Loopback Test,
Analog Loopback with Self-Test, and Remote Digital Loopback with Self-Test can all be
AT&T0
selected from the terminal. Use the
command to terminate the test.
13.2.1 Analog Loopback Test (AT&T1)
This test can check almost every part of the modem and RS-232 cable except the
telephone line outgoing interface. During Analog Loopback testing, data from the terminal
or computer is sent through an RS-232 cable into the modem's transmitter and is
modulated to an analog signal then loopbacked to the receiver, demodulated to digital
form and sent through the RS-232 cable back to the terminal or computer's screen. You
can tell if anything is wrong by looking at the screen. The screen should show the data
you have sent to the modem.
The U-90E will have the TST LED On during the test. This test can only be initiated while
the modem is off-line
13.2.2 Analog Loopback with Self-test (AT&T8)
This test generates data from the modem itself instead of input data from the RS-232
interface. The data will go through the same path as it would be with the Analog Loopback
Tes In the asynchronous mode, the pattern consists of printable ASCII characters.
This test can only be initiated when the modem is off-line. The U-90E modem's TST LED
flashes for any bit error.
13.2.3 Local Digital Loopback Test (AT&T3)
This test will loopback the digital form data demodulated from the receiver to the input of
the transmitter. During testing, all data received from the remote modem will be returned
to the remote modem. This test is applicable when the remote modem does not provide
V.54 Remote Digital Loopback capability
Diagnostics
13-2
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