USRobotics V.34 user manual Options are as follows, RS-232 Signal Operations

COURIER HIGH SPEED MODEMS

The options are as follows.

&N1	300 bps	&N9	16.8K bps (HST, terbo,
&N2	1200 bps		V.FC, and V.34 only)
&N3	2400 bps	&N10	19.2K bps (terbo, V.FC,
&N4	4800 bps		and V.34 only)
&N5	7200 bps	&N11	21.6K bps (terbo, V.FC,
&N6	9600 bps		and V.34 only)
&N7	12K bps	&N12	24K bps (V.FC and V.34 only)
&N8	14.4K bps	&N13	26.4K bps (V.FC and V.34 only)
		&N14	28.8K bps (V.FC and V.34 only)

RS-232 Signal Operations

&Cn Carrier Detect operations. At power-on and reset, the modem operates according to the setting of DIP switch 6. This command is not stored in nonvolatile memory as a power- on/reset default.

&C0	CD override, CD always ON.
&C1	Normal CD operations. The Courier sends a CD signal
	when it connects with another modem and drops the CD
	when it disconnects.

&Dn Data Terminal Ready (DTR) operations. At power-on and reset, the modem operates according to the setting of DIP switch 1. This command is not stored in nonvolatile memory as a power- on/reset default.

&D0	DTR override. The modem operates as though the DTR
	is always ON.
&D1	Advance usage: If issued before connecting with another
	modem, the modem can enter online command mode
	during a call by toggling DTR. (Most communications
	software packages have a method for toggling DTR.)
	&D1 functions similarly to the escape code (+++), except
	that this setting is independent of DIP switch 9.
	If DIP Switch 1 is ON (DTR override) when you issue the
	&D1 command, the DTR override is automatically turned
	off. However, if you change the setting of DIP switch 1
	after issuing &D1, the DIP switch setting takes
	precedence.

Data Mode Operations 4-23