Intel MD566X manual Class 1 DTE-Generated Hdlc Frame Information AT+FTH=mod

56K V.92 Data, Fax, and Voice Chipset

After receiving a frame correctly using the AT+FRH command (FCS is OK), the DCE returns an “OK” message to the DTE. If the frame is received in error (FCS is not OK, carrier is lost, or data is lost due to data overflow), the DCE returns an “ERROR” message to the DTE; the DTE should then discard the frame.

Note: If the telephone line is on-hook, the modem responds back to the DTE with an ‘ERROR’ message whenever any of the fax AT commands, except the +FCLASS command, are sent to the modem.

Address

Field

Control

Field

Facsimile

Control

Field

Facsimile

Information

Field

Figure 5-2. CLASS 1 DTE-Generated HDLC Frame Information

(AT+FTH=<mod>)

		Facsimile	Facsimile	Frame
Address	Control			Checking
		Control	Information
Field	Field			Sequence
		Field	Field
				(FCS)

Figure 5-3. CLASS 1 DTE Reception of HDLC Frame Information

(AT+FRH=<mod>)

Like the data modem mode, the DTE needs to issue an ATD string or ATA command to the modem to originate or answer a fax call. Unlike the data modem mode, auto-answering is not supported by the modem while in fax mode. It is recommended that S-register S0 be set to “0” (that is, use ‘ATA’) whenever the modem is expected to receive a fax call.

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.

Programmer’s Guide Intel Confidential 75