Apple Express Fax/Modem - Manual (Page 143)

&D n DTR options Bus modems do not have a DTR line. For bus modems,
an on-to-off DTR transition occurs when you close the connection tool
or the application currently using the modem. In this case, the modem
goes on-hook.
This command has no effect and remains for scripting compatibility.
0-3 Return OK. Default value is 3.
&F Recall default profile The current active profile is replaced by the
default factory configuration.
&Gn Guard tones This command specifies whether guard tones should be
transmitted. Guard tones are used in some telephone systems to allow
proper data transfer over the network. They are not used in the United
States.
0 Disables guard tone.
1 Same as 2.
2 Sends 1800 Hz guard tone.
&K n Local flow control This command specifies which kind of local flow
control is used. Since bus modems have built-in flow control
mechanisms between the DTE and the DCE, this command has no
effect. Flow control characters generated by the application software are
always passed to the line.
This command has no effect and remains for scripting compatibility.
0-5 Respond OK, no action taken.
&L n Switched/Leased line This command affects the modem’s behavior
during the call setup and carrier handshake phases at the beginning of a
connection.
0 Selects switched (dial-up) line.
1 Selects conditioned leased line.
&P n Pulse mode make/break ratio
0 Sets the dial pulse make/break ratio at 39%/61%.
1 Sets the dial pulse make/break ratio at 33%/67%.
131 M O D E M C O M M A N D S E T