Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version VT3.4 8/17/84; site vortex.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!mcnc!decvax!vortex!lauren From: lauren@vortex.UUCP (Lauren Weinstein) Newsgroups: net.micro.pc Subject: Re: Additional COM ports available for PC's Message-ID: <421@vortex.UUCP> Date: Fri, 19-Oct-84 07:44:12 EDT Article-I.D.: vortex.421 Posted: Fri Oct 19 07:44:12 1984 Date-Received: Sun, 21-Oct-84 15:03:27 EDT References: <9478@watmath.uucp> Organization: Vortex Technology, Los Angeles Lines: 18 Note that unless very specialized software is going to be used, the practical limit on PC serial ports will usually be 3. This is accomplished by buying a 2 port serial add-on board (like the AST cards) to provide COM1 and COM2. Then, a third port may be added as COM3, *if* you are willing to steal one of the (few) interrupts from some other device. In my case, I have a modified standard PC async port that is addressed at an unusual location. I use the printer interrupt for this third async line, and let the printer run busy wait instead of interrupt driven (no big deal -- it all works fine). However, the critical point is that as soon as you go beyond 3 ports (unless you are willing to steal yet another interrupt from the system) you start getting into complex interrupt-sharing techniques that will be by definition completely non-standard and incompatible with much (or most) software that uses the async lines. --Lauren--