Your opinion wanted!
Most Hayes modems use commands to control the behavior of RS-232 circuits.
Among these are the &C command, which controls the behavior of the "Carrier
Detect" circuit, and &D, which controls the behavior of the "Data Terminal
Ready" circuit.
&C0 (the current default) causes the Carrier Detect circuit to be
constantly in the ON condition. &C1 causes the circuit to be ON only when
carrier is actually present on the line. The &C0 default was selected
because some software, particularly those which use the PC ROM BIOS serial
port routines, are unable to even send commands to the modem if CD is in
the OFF condition. However, virtually all recent comm software expects CD
to reflect the actual line condition. This means that users of such
software very often must change to &C1 and save this in the modem's
non-volatile memory.
&D0 (the current default) causes the modem to assume that DTR is always ON
from the terminal or computer (DTR is ignored). &D1 causes the modem to
return to command state on an ON-to-OFF transition of DTR; &D2 causes the
call to be disconnected and auto-answer to be supressed; &D3 causes the
call to be disconnected and the modem to be reset to its stored profile.
Most recent comm software expects a drop in DTR to result in the call being
disconnected, which again means that users often have to change the stored
profile from the default &D0 to &D2.
The Systems Engineering department at Hayes is studying whether the factory
defaults should be changed to &C1 and &D2. The decision will be based on
whether or not selection of these defaults would still, as it has in the
past, make it impossible for some people to use or configure our modems.
If acceptable workarounds would exist, however, the greater convenience for
the majority of users of not having to change these defaults would justify
the change.
If you have an opinion on this matter, particularly if you are aware of
programs or applications which would be negatively affected by this change,
please contact me by email. Thanks!
— Toby Nixon, Principal Engineer, Hayes Microcomputer Products Inc.