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536EX Chipset Developer’s Manual 67
Intel Confidential
Fax Class 1 AT Commands
The ATDT <telephone number> command string causes the modem to originate a fax call. After
dialing the telephone number, the modem sends out a calling tone (1100 Hz), recognizes the remote
fax modem answer tone, and looks for the remote fax HDLC flags at 300 bps. If the HDLC flags
are detected, the modem sends the DTE a ‘CONNECT’ message followed by the Class 1 HDLC
frame information. If the HDLC flags are not detected within the time limit defined by S-register
S7, the modem sends a ‘NO CARRIER’ message to the DTE and then hangs up the line. If the
modem hangs up the line while processing the ATD command (that is, while the modem is on-
hook), the modem responds back with an ‘ERROR’ message whenever the DTE issues one of the
data stream AT commands.
The ATA command causes the modem to answer a fax call. After going off-hook, the modem sends
the answer tone followed by HDLC flags. The modem then sends a ‘CONNECT’ message to the
DTE and waits to receive the HDLC frame information from the DTE. In general, the ATA
command performs three functions:
1. It places the modem off-hook.
2. It causes the modem to transmit the answer tone.
3. It causes the modem to act as if it received an AT+FTH=3 command from the DTE.
The following data mode and voice mode AT commands are supported in fax mode:
Data: All
Voice: +FCLASS, +VDR, +VNH, +VIP, and + VCID
Table 24. Fax Mode Command Descriptions
Command Default Description
+FCLASS
=1
0
Fax Mode Selection: This command is used to select a fax class, indicate current fax
class mode setting, and indicate supported fax classes. All fax mode commands,
except for +FCLASS, are valid only in fax mode.
+FCLASS? Indicates current fax class selection
+FCLASS = ? Indicates supported fax classes
+FCLASS = n Configures DCE for selected fax class. The modem
responds back with an ‘OK’ message at the same
DTE-to-modem data rate used to issue this command
Range: 0, 1, 8
n = 0* Configures DCE for data modem operation
n = 1 Configures DCE for fax Class 1 modem operation
n = 8 Configures DCE for IS-101 voice mode
NOTE: An asterisk (*) denotes the factory-default setting.