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56K V.92 Data, Fax, and Voice Chipset
74 Intel Confidential Programmer’s Guide
bytes of fax data before sending it to the remote modem (AT+FTM command). If the modem
detects the two terminating characters <DLE><ETX> within the data stream, it transmits the data
immediately to the remote modem without waiting for the buffer to fill up.
When the modem transfers data to the DTE, the DTE must filter the data stream by removing all
character pairs beginning with <DLE>. The DTE also must recognize <DLE><ETX> as the stream
terminator. Upon detecting <DLE><DLE>, the DTE must reinsert a single <DLE> in its place. The
modem buffers up to 512 bytes of fax data received from the remote modem if the DTE cannot
read the data immediately (AT+FRM command).
For the AT+FTH and AT+FRH commands, data is sent and received using HDLC formatting. The
format for HDLC framing is provided below. When sending the HDLC data, the modem
automatically generates the flags and the frame checking sequence (Frame Check Sum). All the
other fields are transmitted to or received from the DTE (that is, these fields are under the control
of the DTE).
Figure 5-1. T.30 HDLC Frame Format
Table 5-2. <mod> Selection Table
Value Modulation
Speed
(bps)
3 V.21 ch 2 300
24 V.27 ter 2400
48 V.27 ter 4800
72 V.29 7200
73 V.17 7200
74 V.17 with short train 7200
96 V.29 9600
97 V.17 9600
98 V.17 with short train 9600
121 V.17 12,000
122 V.17 with short train 12,000
145 V.17 14,400
146 V.17 with short train 14,400
FlagFlag
Address Control
Facsimile
Control
Facsimile
Information
Frame
Checking
Sequence
Flag
FieldField
Field Field
(FCS)