Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 171)

AN93
Rev. 1.3 171
6.11. Telephone Voting Mode
The telephone voting mode (TVM) of operation monitors the line to detect polarity reversals after dialing. It waits for
a busy tone to be detected and reports POLARITY REVERSAL or NO POLARITY REVERSAL followed by OK.
To enable TVM, use the G character in the dial string (eg. ATDTG1). The G character must be used for each TVM
call. The S7 timer operates during TVM and indicates NO CARRIER if a timeout occurs before the busy tone is
detected. Polarity reversal monitoring begins after the last digit is dialed and ends at the detection of the busy tone.
Any loss of line-side power (drop out) is considered a polarity reversal if loop current is restored within U51
milliseconds.
6.12. V.92 Quick Connect
The Si2493 supports ITU-T V.92 shortened Phase 1 and Phase 2 to decrease the time required to connect to a
server modem using the V.90 modulation. After the first call, the Si2493 will retain line parameters that allow it to
use shortened Phase 1 and 2 to reduce the total negotiation time. If line conditions change or the remote server
does not support the shortening of these phases, the modem will automatically connect with the normal Phase 1
and Phase 2 negotiation unless specifically commanded not to. Two AT commands control this feature: AT+PQC
and AT+PSS.
The AT+PQC command controls the enabling and disabling of shortened Phase 1 and Phase 2 individually
according to Table 108. It is recommended that both shortened phases be used to realize the maximum reduction
in connect time. The possible settings of the AT+PSS command are shown in Table 109. The AT+PSS command
may be used to force quick connect by setting AT+PSS = 1; however, this is not recommended because calling a
server that does not support this feature will result in a failed connection.
Table 107. Possible +PMHT Settings
<Value> Description
0 Deny V.92 Modem-on-Hold Request
1 Grant MOH with 10 second timeout
2 Grant MOH with 20 second timeout
3 Grant MOH with 30 second timeout
4 Grant MOH with 40 second timeout
5 Grant MOH with 1 minute timeout
6 Grant MOH with 2 minute timeout
7 Grant MOH with 3 minute timeout
8 Grant MOH with 4 minute timeout
9 Grant MOH with 6 minute timeout
10 Grant MOH with 8 minute timeout
11 Grant MOH with 12 minute timeout
12 Grant MOH with 16 minute timeout
13 Grant MOH with indefinite timeout