Multi-Tech Systems MT5600BL - Manual (Page 102)

MultiModemII User Guide
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2. Dial the remote modem and establish your online connection.
3. Type the escape sequence +++AT and press E NTER to bring your modem into
online command mode.
4. Type AT&T3 and press E NTER . Once you receive an OK message from your mo-
dem (if responses are enabled), your modem is placed in digital loopback mode.
5. Have someone enter data from the remote keyboard. For this test, typing multiple
uppercase U characters is a good way to send an alternating test pattern of binary
ones and zeros. The data received by your modem enters its analog receiver, is
converted to digital data, is reconverted into analog, and then is transmitted
back to the remote modem. Your modem passes this test if the data received on
the remote monitor is the same as the data entered from the remote keyboard.
6. To exit the test, turn off the modems.
Note: You can also start and stop a local digital loopback test by using the front panel
LCD and buttons. See “Diagnostic Options Trunk” in Chapter 3.
Back-to-Back Test
This test verifies proper operation by connecting two MT5600BLs back to back using
an RJ-11 cable. By using an MT5600BL that is known to be good, you can test a second
MT5600BL that is suspect.
Computer or Terminal
Digital Analog
Local MultiModem MultiModem under test
Digital Analog
UUUUUUUUUUU
UUU
Jumper RJ-11 cable
Figure C-4. Back-to-back test.
1. Connect two MT5600BLs by plugging an RJ-11 cable into their LEASED jacks.
2. Set the terminal and modems to the same serial port speed. For instance, if you
are using a terminal that is limited to 9600 bps, set the modems to 9600 bps by
sending the command AT$SB9600&W0 to each modem.
3. Following the instructions in Chapter 7, set both modems to two-wire leased-
line mode. One should be set as the originate modem and the other as the an-
swer modem, but it does not matter which is which.
4. Turn on both units and wait for carrier detect (CD).
5. On the modem under test, short pins 2 and 3 of the RS-232C connector with a
paper clip or other metal device.