14-8 CHAPTER 14: TESTING THE CONNECTIONTesting Using aBuilt-in Test Pattern(AT&T7)This test option causes the modem to perform a remote digital loopbacktest by sending a built-in test pattern. An internal error detector countsany errors and, when the test is ended, sends the number of errors or 000(no errors) to the screen.Follow the steps below. However, you don't need to type anything duringthis test. The modem sends only its final error count to your screen.1 Send AT&M0&N3S14.0=0 to prepare the Business Modem for testing.This command disables error control, fixes the connection rate at 2400bps, and makes the Business Modem return to command mode whenyou type the escape code (+++).2 Establish a connection with the remote device.3 If you haven't already done so, arrange with the remote user tocooperate with the test.If necessary, set the remote device to acknowledge the remote digitalloopback request. For example, older 3Com modems need to be set toS16=8.4 Send AT&T7 to the modem. The modem enters remote digital loopbackmode, and the MR status light flashes.The Business Modem sends its built-in test pattern to the remote device,which loops it back to your Business Modem. You will not see the data onyour screen.5 Send the escape code, +++, and then AT&T0 to end the test. You can alsoend the test by sending ATH, ATZ, or ATZ! Be careful, though, becauseATZ and ATZ! reset the Business Modem in addition to ending the test.If you issue an invalid command, the Business Modem sends an ERRORmessage. If you set Register S18, the Business Modem automatically endsthe test when the test timeout is reached. See the example in theprevious section, Stopping a Test for an example of using S18.When the test ends, the Business Modem returns a three-digit code,followed by OK. A code of 000 indicates no errors were found; a code of255 indicates 255 or more errors.Data errors indicate a problem with the remote device or with the phonelink.6 Send AT&M4, unless you used a reset command (ATZ or ATZ!).
