MultiModemDSVD User Guide | C Loopback Tests |
3.Dial the remote modem and establish your online connection.
4.Type the escape sequence +++AT and press ENTER to bring your modem into online command mode.
5.Type AT&T6 and press 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 online com- mand mode and enters data mode.
6.Enter data from your keyboard. For this test, typing multiple uppercase U char- acters is a good way to send an alternating test pattern of binary ones and zeroes. Data received by the remote modem enters its analog receiver, is converted to digital data, is reconverted into analog, and then is transmitted back to your modem. Your modem passes this test if the characters received on your monitor are the same as entered from your keyboard.
7.To exit the test, type the escape sequence +++AT and press ENTER. This puts the modem in online command mode. The modem should respond with an OK mes- sage. If you wish to stay on line with the remote modem for normal data trans- mission, type AT&T and press ENTER to exit the test, then type ATO and press ENTER to return on line. If you wish to terminate the call, type ATH and press ENTER to hang up.
Local Digital Loopback Test (V.54 Loop 2)
The local digital loopback test is identical to the remote digital loopback test with one exception. Instead of using your modem to signal a remote modem to place it- self in digital loopback mode, your modem is placed in digital loopback mode while the remote modem is not. Data is entered and transmitted from the remote modem, sent across the phone line to your modem, and looped back to the remote modem.
AT&T3
OK
UUUUUUUUUUU UUU
Digital Analog | Analog Digital | ||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Computer or Terminal Local MultiModem | Remote MultiModem Computer or Terminal |
Figure C-3. Local digital loopback test
Test procedure
1.Open your communication software and go into terminal mode. Type AT and press ENTER; you should get an OK message. Type AT\N and press ENTER to dis- able error correction. Type AT+MS=9,1,9600,9600 and press ENTER to set the lo- cal modem to V.32 mode at 9600 bps.
2.Dial the remote modem and establish your online connection.
66