Loopback Tests - ZyXEL Communications U-336S User Manual

temporary power-on reset problem and will not affect modem
operation.

Loopback Tests

The Analog Loopback Test, Local Digital Loopback Test, Remote
Digital Loopback Test can all be initiated with AT commands from the
terminal. Use the AT&T0 command to terminate the test.
Analog Loopback (AT&T1)
This test can check almost every part of the modem and the 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 it is looped back 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.
This test can only be initiated while the modem is off-line.
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 with the Analog Loopback Test. In asynchronous mode, the
pattern consists of printable ASCII characters. You can see the result
on the screen. In the synchronous mode, the pattern is made up of
scrambled binary 1 and the Throughput Meter will change to a Bit Error
Rate Meter. The left reader displays accumulated bit errors while the
right reader displays accumulated bits sent.
This test can only be initiated when the modem is off-line. The following
Bit Error Rate Meter example shows 11120 Kbits sent, 22 bits in error.
When the number exceeds 99999 Kbits, it will reset itself back to zero.
130 Diagnostics & Troubleshooting