AC International MTA128ST-USB manual String normally it is issued by itself ATZ

MultiModemISDN User Guide

	result is the same as turning the modem off and on. When you enter ATZ,
	the state of the &W command determines where the default values originate.
	The &W0 defaults come from the customized configuration in NVRAM, and
	&W1 defaults come from the factory default configuration in ROM. Because
	Z clears the command buffer, it must be the last command in a command
	string; normally it is issued by itself: ATZ.
	Note that whereas the &F0 reset command always restores the factory
	default profile, the Z reset command restores either the factory default or the
	stored profile, depending on how the &W command is set.
Command: &Cn
Function:	DCD Control
Values:	n = 0, 1, or 2
Default:	&C1 (DCD normal)
Description:Controls behavior of the DCD (Data Carrier Detect) signal (pin 8 on the
	RS232E/V.24 interface). Normally, DCD goes high when the TA establishes a
	connection and drops when the connection is lost. However, you also can
	force DCD to remain high at all times or to remain high except for a brief
	drop following a disconnect.
	&C0 DCD is forced high at all times
	&C1 DCD goes from low to high when TA establishes a connection (DCD
	normal)
	&C2 DCD drops briefly following disconnect, then goes high again. Register
	S10 defines how long DCD signal remains low after disconnect
Command: &Dn
Function:	DTR Control
Values:	n = 0, 1, 2, 3, or 4
Default:	&D1 (exits data mode and re-enters AT command mode)
Description:Controls how TA responds to DTR (Data Terminal Ready) signal on pin 20 of
	RS232E/V.24 interface. A high DTR signal tells the TA that the connected
	computer is ready to communicate.
	&D0 TA ignores the DTR signal
	&D1 When DTR goes low, TA exits data mode and re-enters AT command
	mode
	&D2 If DTR goes low, when TA is on-line, the TA hangs up, returns to
	command mode, and disables autoanswer. If TA is offline, it neither
	answers nor dials while DTR is low.
	&D3 When DTR goes low, TA resets the data port and disables
	autoanswer. If DTR goes low when TA is online, TA hangs up, resets
	active configuration to the stored configuration, and disables
	autoanswer.

Note: If the user wants to accept calls while DTR is low, the TA must be configured to ignore DTR. To do this, enter AT&D0<cr>. With this configuration, the TA is able to accept calls while DTR is low. If this configuration setting is not made, the TA rejects incoming calls until DTR is high while the calls comes in.

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