This is the pinout of the serial connectors. As we shall see below, there is an easy method for matching this to RS-232. We are now carefully removing the pins from the connector, soldering the wires to the pin, then replacing the pin in the connector body. On later Macintoshes there are logic and a line driver for this line. SOME of the older terminal programs don't have the code to explicitly drive HSKo high.
SOME terminal programs drop HSKo when they close down.
SOME modems require DTR and will drop carrier if DTR goes away. Of course, some people consider B a feature, in that it will hang up the phone when you switch off the computer. Personally, I hang up the phone when I am done and I like to switch from terminal program to terminal program. If one of the above conditions happen, there are only three alternatives. Look for a DIP switch for this.