56K V.92 Data, Fax, and Voice Chipset
3.9 Diagnostic Testing [S18, &Tn]
The &Tn command initiates loopback tests. Setting S-register S18 to a non-zero value determines the length of testing after the modem receives the &Tn command. After the testing period elapses, the modem halts the test and returns to command mode. To abort the test before the test timer has timed out, enter the escape code sequence followed by AT&T0. Setting S18 to an ’0’ disables the test timer. In this case, the loopback test continues to run until an escape code, followed by AT&T0 (or ATH), is sent to the modem.
The modem provides a local analog loopback test (see Section 3.9.1) and local analog loopback self-test (see Section 3.9.2) for testing modem-to-modem and DTE-to-modem communication integrity in all modes except V.90 and V.92. After entering the loopback mode, the communication integrity is checked by the DTE sending data to the modem and then checking the looped-back data for errors. In addition, in the self-test mode the modem implements an internal data pattern generator and checker that detects errors. When a data error occurs in self-test mode, the modem increments an internal error counter. Upon completing the test, the modem sends a three-digit error count to the DTE. These tests are illustrated in the following examples.
3.9.1 Local Analog Loopback [AT&T1]
This test is used by the local DTE to check the DTE-to-modem communication integrity. The local DTE will not initiate the test from online command mode.
LOCAL MODEM
TRANSMITTER
RECEIVER
Figure 3-2. Local Analog Loopback Test
Local Modem (or Test Modem)
AT&F &W<CR> | Returns the modem to the factory de- |
| faults. |
AT S18 = 0 &T1 | Causes the modem to run local analog |
| loopback without self-test. |
CONNECT 115200 | Modem response code indicates that an- |
| alog loopback is enabled with a DTE |
| speed of 115200. |
This is a test. | Test string that the user could type at |
| the keyboard. If the received data is |
36 | Intel Confidential | Programmer’s Guide |
