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536EX Chipset Developer’s Manual 65
Intel Confidential
Fax Class 1 AT Commands
The fax AT+FCLASS command is used for changing between fax classes, determining the current
class selection, and determining the supported fax classes. Both data/fax Class 0 (data modem
mode) and Class 1 (fax modem mode) are implemented by the modem. In Class 0, the DTE-to-
modem data rate can be set from 300 bps to 115,200 bps. In Class 1, it is recommended that the
DTE-to-modem data rate is set to 19,200 bps.
The silence-time timers consist of AT+FTS=<TIME> and AT+FRS=<TIME>. Silence time is
defined as the length of time when the modem neither receives nor transmits energy (that is,
modem transmit carrier) on the telephone line.
The modem exchanges streams of data with the DTE while executing the data transfer commands
AT+FTM=<mod>, AT+FTH=<mod>, AT+FRM=<mod>, and AT+FRH=<mod>. The values
supported for <mod> are provided in Table 23.
During data transfer, an ASCII
<DLE> character ($10h) is used as a special character to shield
other special characters.
Special characters in the data stream are used in the following way:
any data ... <DLE><ETX> end of data stream
any data ... <DLE><DLE> single 10h<DLE> in data stream
any data ... <DLE>
<not DLE or ETX> delete both <DLE> and next character
When the DTE transfers data to the modem, the DTE must insert a <DLE> for each <DLE> in the
original data stream. In addition, when data is no longer available, the DTE must add the stream
terminator
<DLE><ETX> to the end of the data stream. The modem buffers up to one thousand
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.
Table 23. <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