Specifications

AN93
130 Rev. 0.9
The following steps will allow the spurious data and bit errors to be eliminated while preserving the valid data.
1. Ignore 19 B0.
2. Use 19 B2 to discard all collected receive data.
The filtered version of the HDLC frames, based on this algorithm, is shown below with the valid data in bold.
0D 0A 43 4F 4E 4E 45 43 54 20 31 32 30 30 0D 0A 19 BE 20 20 19 B1 19 B0 19 B2 30 93
19 B1 19 B2 30 93 19 B1 19 B2 30 93 19 B1 19 B2 30 93 19 B1 19 B2 19 B2 B6 9E F7 46
19 B0 19 B2 29 C6 19 B0 19 B2 FF 98 89 18 19 B0 19 B2 92 6E EF 14 65 19 B0 19 B2 DA
BE C6 07 EA D8 31 C2 05 3C FA C8 86 C4 40 E6 19 A0 CA EA A8 F9 19 B2 8D 00 57 A5 43
29 19 B0 19 B2 05 CB 14 9F 7C 2D 19 B0 19 B2 19 B2 19 BA 0D 0A 4E 4F 20 43 41 52 52
49 45 52 0D 0A
3.5.17. Modem-On-Hold
The Si2493 supports modem-on-hold as defined by the ITU-T V.92 specification. This feature allows a connected
Si2493 to place a server modem-on-hold while a second call, typically a voice call, uses the phone line. The
maximum time the modems will remain on-hold is controlled by the modem receiving the modem-on-hold request.
Once the second call has completed, the Si2493 will reinitiate the data connection if the time elapsed has not
exceeded the time negotiated by the two modems. The Si2493 can also be placed on hold itself by a remote
modem allowing a far-end user to make or receive a voice call. Modem-on-hold is only supported on the Si2493 for
V.34 (14400–33600 bps) and higher speed modulations. The AT+PMH command is used to enable (+PMH = 0) or
disable (+PMH = 1) modem-on-hold.
3.5.17.1. Initiating Modem-On-Hold
Modem-on-hold is typically initiated when a connected client modem receives a subscriber alert signal (SAS) tone
as described in "3.5.4. Type II Caller ID/SAS Detection" on page 112. However, it may be initiated any time the
modem is on-line in command mode. The AT+PMHR command is used to initiate a modem-on-hold request. After
this command is issued, the modem will place a modem-on-hold request to the server, and the +PMHR: command
response will indicate the server’s response to the request. The possible responses may be seen in Table 87.
19 B0 Followed by a data byte with > 6 mark bits in a row. The
modem looks for HDLC flags.
19 B2 HDLC Flag detected
Beginning of Packet
05 CB 14 9F 7C 2D
Spurious data
19 B0 Followed by a data byte with > 6 mark bits in a row. The
modem looks for HDLC flags.
19 B2 HDLC Flag Detected
19 B2 If there is 1 bit error received in an HDLC flag, the
modem assumes a new single-byte packet. Since a 1-
byte packet is invalid, 19 B2 is generated by the modem.
19 BA Loss of Carrier Detected
0D 0A 4E 4F 20 43 41 52 52 49 45 52 0D 0A NO CARRIER
Table 86. Bit Errors (Continued)
Data Meaning