Re: 14.4 Modem: "CD" indicator light remains on

[dempson@actrix.gen.nz (David Empson)]

Phoenyx <quazar@dcnet2000.com> wrote:

> No, it was possible to drop the carrier signal on most PC comm
> programs to hangup the modem.

That would be a neat trick.  As I said, the carrier detect signal is an
INPUT to the computer.  There is no way the computer can "drop the
carrier detect signal".

It can indirectly cause the modem to make the carrier detect signal go
false, by telling the modem to hang up.  This was usually done by
setting the DTR signal (from the computer to the modem) false, or if not
supported (e.g. IIgs or Mac), then the software issued the "three
plusses" escape sequence and an ATH command.

The term "drop the carrier signal" is probably referring to the
connection between the two modems, not the carrier detect input to the
computer, which tells the computer that there is a valid carrier
betweens the modems.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand