Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 117)

AN93
Rev. 1.3 117
Bit 6 (ADD) attempts DTMF dial, then falls back to pulse dialing if unsuccessful. The first digit is dialed as DTMF. If
a dial tone is still present after two seconds, this suggests that the DTMF digit was not taken into account by the
central office. In that case, the ISOmodem redials the first digit and remaining digits as pulses. If a dial tone is not
present after two seconds, the ISOmodem assumes that the first DTMF digit was recognized and dials the
remaining digits as DTMF. However, in a typical PBX environment, where dialing a DTMF digit (typically 8 or 9) is
required to obtain an outside line, this method does not give any indication that the outside line can accept TDMF
dialing.
Bit 1 (HDLC) controls whether the normal asynchronous mode (default) is used or the transparent HDLC mode is
enabled. See "5.14. Legacy Synchronous DCE Mode/V.80 Synchronous Access Mode" on page 125 for more
details on these modes.
Bit 0 controls whether the normal ITU/Bellcore modem handshake (default) or a special fast-connect handshake is
used. Fast connect is typically used in specialized applications, such as point-of-sale terminals, where it is
important to connect and transfer a small amount of data rapidly (see Table 79).
Table 79. U7A Bit Map
Bit Name Function
15 V29FC Enable V29 Fast Connect; used in conjunction with AT +FCLASS=1.
1 = Enable
0 = Disable
14 CNSMS Chinese EPOS SMS enable
1 = Enable
0 = Disable
13 V29EM Use EM shielding to change direction of half duplex V.29FC.
0 = EM shielding
1) <EM><rrn>=<0x19><0xBC> to receive a V29FC packet.
2) <EM><rtn>=<0x19><0xBD> to send a V29FC packet.
1 = RTS pin toggle.
12 Reserved Read returns zero.
11 ARMLO 0 = Normal operation.
1 = Accomodate remote modem with large clock offset, such as 340 ppm. May degrade
training for normal modems; enable only when necessary.
10:8 Reserved Read returns zero.
7 DOP 0 = Normal ATDTW operation.
1 = Use ATDTW for pulse/tone dial detection (see "6.10. Pulse/Tone Dial Decision" on page
169 for details).
6 ADD Adaptive Dialing.
1 = Enable
0 = Disable
5 Reserved Read returns zero.
4 NEWFC New V.22 handshake enable. This bit is mutually exclusive with bit 0. This bit makes hard-
coded U80 timing unnecessary. Without this bit, the appropriate value in U80 is required.
3:2 Reserved Read returns zero.
*Note: When HDLC or FAST is set, the \N0 (Wire mode) setting must be used.