APPENDIX F. MODEM TESTING Testing is available with the &T command or Register S16. All loopback testing conforms to CCITT Recommendation V.54. Earlier USRobotics high speed modems, however, did not perform the &T test repertoire. NOTE: Only one test can be performed at a given time. If you send a test command while the modem is in test mode, you'll receive an ERROR message. TESTING WITH &T The tests supported through the &T command include analog loopback, digital loopback and remote digital loopback. Users can key in their own data during testing, or use the modem's internal test pattern and error detector. In all cases, disable error control before testing. If the modem is detecting errors and retransmitting the affected data, your results will be invalid. During testing, the MR status light flashes. Ending a Testę&T0, S18 Issuing the &T0 command terminates a test. Alternatively, set Register S18 to a specified number of seconds, for example, S18=10. When the 10 seconds are up, the modem automatically ends the test and returns to Command mode. If the test was Analog Loopback, the &T0 command hangs the modem up. If the test was Digital or Remote Digital Loopback, issue an ATH command to hang up the modem, or an ATZ command to hang up the modem and reset it to its defaults. NOTE: If you use the S18 test timer, but in the process of testing you issue an ATZ command, S18 resets to zero and the timer is disabled. You cannot store a value for S18 in nonvolatile memory: its power-on and reset default is always zero. ANALOG LOOPBACKę&T1, &T8 This test checks the operation of the modem's transmitter and receiver. Data flow is shown in Figure F-1. Figure F-1. Data Flow During Analog Loopback There are two analog loopback options. The first, &T1, involves your typing data that you can verify at your screen. The second option, &T8, is an internal self-test that does not involve the keyboard or screen. It isolates the modem from the computer interface to give you a more specific result. NOTE: HST or Dual Standard modems must be tested at 2400 bps or lower to avoid asymmetrical modulation at higher speeds. &T1 1. If you are testing an HST or Dual Standard modem, set your terminal or software to 2400 bps. 2. The modem must be in Command mode. If you wish, set Register S18 as a test timer, as explained earlier. 3. Send the modem the following command. AT &M0 &T1 The modem disables error control, enters analog loopback (AL) mode, and sends a CONNECT message. The MR status light flashes. 4. Type recognizable data so that you can verify it when it is looped back to the screen. 5. End the test. If you set S18, the modem automatically stops the test at the timeout, exits AL mode and responds OK. If you didn't set Register S18, wait one second and type +++ to bring the modem back to Command mode. If DIP switch 9 is UP, the modem also hangs up and ends the test. If DIP switch 9 is DOWN, type AT&T0 to end the test. Or send either ATH or the command that resets the modem, ATZ. The latter two commands end the test and hang up the modem. The modem responds OK. If the modem sends an ERROR message, you have issued an invalid command. 6. If there were no errors, reset the modem to &M4, for error control, unless you've issued the ATZ reset command. NOTE: If the modem is in online- command mode, that is, still connected to a remote modem, and you send it an &T1 or &T8 command, it drops the call, enters AL mode, sends a CONNECT result and waits for loopback characters. &T8 This AL option causes the modem to send an internal test pattern to its transmitter and loop it back to the receiver. An internal error detector counts any errors and, when the test is ended, sends the number of errors or 000 (no errors) to the screen. Since you don't type anything during this test, and the modem does not send anything to the screen, this option verifies only the modem. If there are no errors but your problem continues, it may be at the computer interface. 1. If you are testing an HST or Dual Standard modem, set your terminal or software to 2400 bps. 2. The modem must be in Command mode. If you wish, set Register S18 as a test timer, as explained earlier. 3. Send the modem the following command: AT &M0 &T8 The modem disables error control and enters AL mode. The MR status light flashes. The modem sends its internal test pattern to the trans- mitter, and loops the pattern back to the receiver. You will not see any data on your screen. 4. End the test. If you set S18, the modem automatically stops the test at the timeout. If you didn't set Register S18, type AT&T0 to end the test. Or use ATH or the command that resets the modem, ATZ. Both of the latter end the test and hang up the modem. The modem hangs up and returns a three-digit code, followed by OK. A code of 000 indicates no errors were found. A code of 255 indicates 255 or more errors. An ERROR message indicates that you issued an invalid command. 5. If there were no errors, reset the modem to &M4 for error control unless you issued the ATZ command. &T2 This option is reserved. DIGITAL LOOPBACKę&T3 If your modem has passed the AL test, this test can help you locate a problem with a remote modem or the telephone channel. Figure F-2 shows the data flow during DL testing. Figure F-2. Data Flow During Digital Loopback NOTE: This test requires the modem to establish a connection and return to online-command mode in response to the +++ escape code. DIP switch 9 must be set DOWN so that the modem does not hang up on receipt of the escape code. After you change the switch, issue ATZ to the modem to initiate the new setting. As with AL testing, HST and Dual Standard modems should be tested at 2400 bps or lower. 1. Set the modem to &M0, to disable error control. HST and Dual Standard modems should be set to 2400 bps or lower to avoid asymmetrical modulation at higher speeds. Establish a connection with the remote modem. 2. Bring the modem back to Command mode with the +++ escape code. Then send it the AT&T3 command. The modem enters DL mode and the MR status light flashes. 3. The remote user should type a short message. It will be looped back by your modem's transmitter for verification on the remote screen. You will not see the message or any other data. 4. When the remote user has completed the test, issue the AT&T0 command to end the test. Or send either ATH or the command that resets the modem, ATZ. The latter two commands end the test and hang up the modem. The modem responds OK. If the modem sends an ERROR message, you have issued an invalid command. 5. Reset DIP switch 9 UP if you normally use the factory default. Reset the modem to &M4 unless you used the reset command, ATZ. &T4, &T5 The &T4 option causes the modem to grant a remote modem's request for a Remote Digital Loopback test. The &T5 option cancels &T4, and the modem fails to recognize such a request. This is the default so that your modem isn't subject to another user calling and tying up your modem without your permission. REMOTE DIGITAL LOOPBACKę&T6, &T7 This test, like the local digital loopback test, verifies the condition of both modems and the phone link. Data flow is shown in Figure F-3. Figure F-3. Data Flow During Remote Digital Loopback The request for and granting of Remote Digital Loopback testing requires that both modems use CCITT V.22 standard signaling. The test must be performed at 2400 bps or lower. If the remote modem does not have the capability or is not set to respond, you will get an ERROR result code. As with Analog Loopback, there are two Remote Digital Loopback options. If you select &T6, you send keyboard data to the modem and verify it when it is returned over the phone lines and to your screen. If you select &T7, the modem sends its internal test pattern and returns an error count to your screen. NOTE: Both test options require the modem to establish a connection and return to online-command mode in response to the +++ escape code. DIP switch 9 must be set DOWN so that the modem does not hang up on receipt of the escape code. If necessary, set the switch DOWN and then issue the ATZ command to the modem to initiate the new switch setting. &T6 1. Set the software to 2400 bps or lower. Set the modem to &M0. If you wish, set the S18 timer. Establish a connection with the remote modem. If you haven't already done so, arrange with the remote user to cooperate with your testing and, if necessary, set the remote modem to acknowledge the RDL request. For example, older USRobotics high speed modems need to be set to S16=8. 2. Bring the Modem back to Command mode with the +++ escape code. Send it the AT&T6 command. The modem enters RDL mode and the MR status light flashes. 3. Type a short message. It will be looped back to your modem by the remote modem and to your screen for verification. (The remote user will not see your data.) 4. End the test. If you set Register S18 the modem automatically ends the test when the test timeout is reached. If you didn't set S18, type AT&T0 to end the test. Or send either ATH or the command that resets the modem, ATZ. The latter two commands end the test and hang up the modem. The modem responds OK. If you issue an invalid command, the modem sends an ERROR message. Data errors indicate a problem with the remote modem or the phone link. If you have not performed analog loopback testing with your modem, the problem may also lie with your modem. 5. Reset DIP switch 9 UP unless you normally set that switch DOWN, and issue ATZ to the modem to initiate the new setting. Reset the modem to &M4 unless you used the reset command, ATZ. &T7 This test option causes the modem to send an internal test pattern through the Remote Digital Loopback. An internal error detector counts any errors and, when the test is ended, sends the number of errors or 000 (no errors) to the screen. You don't need to type anything during this test. The modem sends only its final error count to your screen. 1. Set the software to 2400 bps or lower. Set the modem to &M0. If you wish, set the S18 timer. Establish a connection with the remote modem. If you haven't already done so, arrange with the remote user to cooperate with your testing and, if necessary, set the remote modem to acknowledge the RDL request. For example, older USRobotics high speed modems need to be set to S16=8. 2. Bring the modem back to Command mode with the +++ escape code. Then send it the AT&T7 command. The modem enters RDL mode and the MR status light flashes. The modem sends its internal test pattern to the remote modem, which loops it back to your modem. You will not see the data on your screen. 3. End the test. If you set S18, the modem automatically stops the test when the timer times out. If you didn't set Register S18, type AT&T0 to end the test. Or send either ATH or the command that resets the modem, ATZ. The latter two commands end the test and hang up the modem. The modem responds OK. If you issue an invalid command, the modem sends an ERROR message. When you terminate the test, the modem returns a three-digit code, followed by OK. A code of 000 indicates no errors were found. A code of 255 indicates 255 or more errors. If you've performed an Analog Loopback and know your modem is working properly, errors indicate a problem with either the phone connection or the remote modem. 4. Reset DIP switch 9 UP unless you normally operate with it DOWN. Issue an ATZ command to initiate the new switch setting. Reset the modem to &M4 unless you've sent it the ATZ reset command. TESTING WITH REGISTER S16 Register S16 is a bit mapped register with the following bit functions: Bit Value Function 0 1 Analog Loopback (AL) 1 2 Dial Test 2 4 Test Pattern 3 8 Remote Digital Loopback (RDL) NOTE: Earlier USRobotics modems require bit 3 to be enabled in order to grant RDL to a remote modem. The modem now requires its default &T4 setting instead. To perform RDL with a USRobotics modem that does not use the &T test repertoire, that modem should be set to S16=8 before it can grant RDL testing. ANALOG LOOPBACK (AL)ęS16=1D As with the &T AL test, do not attempt this test under error control. HST and Dual Standard modems should be tested at 2400 bps or lower, to avoid asymmetrical modulation at higher speeds. To use the modem's Test Pattern (S16, bit 2) instead of typing your own data, see Test PatternęS16=4 later in this appendix. 1. To initiate testing, type AT&M0S16=1D. The modem disables error control, enters AL mode and sends a CONNECT result code. The MR status light flashes. 2. Type data to the modem for the modem to transmit, loop to its receiver, and output to the screen. An alternative is to use the Test Pattern, described later. 3. End the test by not typing anything for one second, then typing three pluses (+++), and waiting another second. This forces the modem back to command mode. If DIP switch 9 is UP, the modem exits AL mode and returns to Command mode. If DIP switch 9 is DOWN, the modem maintains the connection when it receives the +++ escape code. Issue the ATH command to end AL mode. 4. Reset the modem to Data mode, S16=0, and error control (&M4), or issue the ATZ (reset) command. DIAL TESTęS16=2 The Dial Test is used for factory testing the frequencies of Touch-Tone values. When S-Register 16 is set to 2 and a single Touch-Tone is dialed (e.g., ATD7 ), the modem continues to transmit that tone until you type another Carriage Return. TEST PATTERNęS16=4 The test pattern can be used instead of your typed data during Analog Loopback (AL) or Remote Digital Loopback (RDL), using &T commands or S16. The test pattern is available at all speeds. At 300 bps, the modem's DTE rate must be fixed (&B1) and the link rate fixed at 300 bps (&N1). At rates over 9600 bps, just set the modem for a fixed DTE rate (&B1). To use the test pattern during AL testing with S16, type the following command. The test pattern is sent through the loopback. AT&M0S16=5D To use the test pattern during RDL testing with S16, type the following command. AT&M0S16=12 To use the test pattern with the &T AL or RDL tests, insert the test pattern command, S16=4, before issuing the test command. The first of the following commands initiates AL, the second RDL: ATS16=4&T1 ATS16=4&T6 The test pattern alone (ATS16=4) is used for testing equipment and the phone line. When S16 is set to 4, the modem transmits the test pattern upon connec- tion with a remote modem. Ending Testing with the Test Pattern Pressing any character key cancels all test pattern tests and hangs up the modem. If you used Register S16, be sure to reset Register S16 to Data mode when you reset the modem to its error control defaults, for example, ATZ or AT&M4S16=0. REMOTE DIGITAL LOOPBACKęS16=8 Responding Modem The responding modem must be ready to act on the Courier's RDL request. USRobotics high speed modems should be set to &T4. If they do not have &T testing capability, they should be set to S16=8. Initiating Modem 1. If DIP switch 9 is UP, set it DOWN so that it does not hang up on receipt of the +++ escape code. Issue an ATZ command to initiate the new switch setting. 2. Set the software to 2400 or 1200 bps. The CCITT-specified RDL signals are defined only for connections at 2400 or 1200 bps. 3. Disable error control by setting the modem to &M0. Then establish a connection with the remote modem. 4. Bring the modem back to Command mode by sending it the escape code: one second of no data, three pluses (+++), and another second of no data. 5. When the OK result code appears, send the modem the following command. ATS16=8 O The modem enters RDL mode (S16=8), the MR status light flashes, and the modem goes back online (O command). Then it transmits the CCITT-defined RDL signals, causing the remote modem to enter RDL mode. 6. Type any data at the keyboard. (Or send the test pattern.) 7. To end the test, send the modem the +++ escape code again to bring it back to Command mode. 8. When the modem sends the OK result, reset the modem to Data mode with the following command. ATS16=0 The modem signals the responding modem that RDL testing is over. Terminate the call as you normally would, and reset the modem to its normal error control setting, &M4 or &M5. Or, if you wish to resume data transmission with the remote modem, add the O command to the ATS16=0 string to return the modem online. Keep in mind, however, that error control is disabled. Because error control is negotiated during the con- nection sequence, its status cannot be changed until the modem is back on hook and in Command mode.