Intel MD566X - Manual (Page 36)

56K V.92 Data, Fax, and Voice Chipset
36 Intel Confidential Programmer’s Guide
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.
Figure 3-2. Local Analog Loopback Test
Local Modem (or Test Modem)
AT&F &W 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
DTE
TXD
RXD
TRANSMITTER
RECEIVER
LOCAL MODEM