ZyXEL U-90E User Guide - Page 124

Loopback Tests, Analog Loopback Test (AT&T1), Local Digital Loopback Test (AT&T3)

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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 selected from the terminal. Use the AT&T0 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 13-2 Diagnostics

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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 selected from the
terminal. Use the
AT&T0
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