Black Box MD1640A, MD1641A manual Back-to-Back Test

CHAPTER 8: Modem Testing

3.Type the Escape Sequence (+++AT<CR> or <BREAK>AT<CR>) which brings your modem into Command mode, while still main- taining the connection with the remote modem.

4.Type ATU2 and hit ENTER. The local modem responds to this command by transmitting an unscrambled marking signal, which causes the remote modem to place itself in Digital Loopback mode. Then the local modem exits Command mode and enters pseudo On-line mode.

5.Type data from your keyboard. For this test, typing multiple upper case "U" characters is a good way to send an alternating test pattern of ones and zeros. The data received by the remote modem will enter its analog receiver, be converted to digital data, be reconvert- ed into analog, and then looped through its transmitter back to the local modem. Your modem passes this test if the data entered from the local keyboard is the same as the data received on your monitor.

8.5Back-to-Back Test

This test lets you connect two Series II Modems with an RJ11 cable to verify proper operation. (See Figure 8-4A on the next page.) Using a Series II Modem that is known to be operational, you can test a second Modem that is suspect.

1.Plug the modular ends of an RJ11 cable into both Modems’ LEASE jacks (336+ models) or LINE jacks (336 models).

2.Force DTR ON in both local and remote modems (Switch #1 DOWN).

3.Enter the command AT$SB9600$BA0&W0<CR> on both local and remote modems. This sets the serial speed to 9600 bps. Make sure that the terminal/computer is also set for 9600 bps.

4.Set both modems in Leased-Line mode (DIP-Switch # 10 DOWN).

5.Set one Series II Modem to Answer enabled (DIP-Switch #5 UP) and the other Modem to Originate enabled (DIP-Switch #5 DOWN). Note that it does not matter which modem (local/remote) is set to Answer/Originate—just so they are set opposite.

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