Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!iuvax!bsu-cs!cfchiesa From: cfchiesa@bsu-cs.bsu.edu (Christopher Chiesa) Newsgroups: comp.sys.ibm.pc Subject: Re: Hardware Weirdness with add-on boards Summary: Comments on comments on Hardware Weirdness Message-ID: <6831@bsu-cs.bsu.edu> Date: 17 Apr 89 19:40:22 GMT References: <6809@bsu-cs.bsu.edu> <2929@ihuxy.ATT.COM> Organization: CS Dept, Ball St U, Muncie, IN, USA Lines: 98 In article <2929@ihuxy.ATT.COM>, vg55611@ihuxy.ATT.COM (Gopal) writes: > In article <6809@bsu-cs.bsu.edu> cfchiesa@bsu-cs.bsu.edu (Christopher Chiesa) writes: > > {stuff deleted} > A few things about COM ports which will help you figure things out: > > 1. COM ports reside at (sets of) physical addresses. Only one COM port > can be set to one range of addresses. The range of addresses are > well defined for COM1 and COM2 but not for COM3,COM4 etc.. Okay... informative but not particularly helpful; read on... > > 2. Usually add-on serial port boards can be configured so that they are at > a specific range of port addresses. You must ensure that there is no > conflict of port addresses. Remember that only COM1 and COM2 have > well defined addresses. > I don't think I have any way of doing this. On the computer-with-modem (call it computer "M"), the modem can be toggle-switched to COM1 or COM2, and the interfering serial/parallel (and game port, even...) card can be set to two different jack-number-to-COM-number (COM1 and COM2 only) corres- pondences OR to a "disable serial ports" position -- but no matter WHAT combi- nation I try, even with "disabled" serial ports, the second board still interferes with the modem -- it merely has to be PRESENT. > 3. Many PCs come with built-in serial ports. Check your hardware manual > to see if there is (are) any. Also, you should know what port it is > set up to be (usually this is COM1 or COM2) so that you know the range > of port addresses that it uses. Based on the (possibly wrong) assumption that a "built-in serial port would 'show' its presence by the presence of a serial port jack on the computer," I can state definitively that NEITHER of the two computers ("M" or the video- thingie one, let's say "V") has a built-in port. On the other hand, if the port can BE there but not SHOW, it's anybody's guess. I don't think EITHER of the owners even HAS a "hardware manual," but I can at least ASK. > > 4. If you have add-on serial ports, ensure that they are at different port > addresses from the built-in ones. No way whatsoever that I am aware of, for me to do this -- can you recommend a technique? The most "technical" manuals available are those covering (mini- mally, I guess) the DIP switch settings; and there's NO mention of "selectable addresses." (I've installed boards on MicroVaxen, so I know the type of set- ting you're talking about, but they appear to be absent on both these PC add- ons...) > > 5. COM ports also generate interrupts when a character comes in. The > interrupt number generated for COM1 and COM2 are well defined. Just > like the port addresses, usually the interrupt number has to be set on > the add-on board when you want it to be COM3, COM4 etc.. Usually > the interrupt numbers used are the same as the ones for COM1 and COM2 > - this means that the software that you are running has to be smart > enough to figure out which COM port generated the interrupt. Many > pieces of software are not that smart. Hmmm... Kermit and other software on Computer M was quite well able to "talk to" the modem once the other card was removed; Computer V was running one pro- prietary package written specifically for use with the card(s) they've got in there. The cards allow you to select "COM1" vs. "COM2" by a slide switch, but that's all.. (It is beginning to sound as though these people are seriously up a creek.) > > 6. Check to see if the software that you run allows you to set up COM3, COM4 > etc. and whether you can tell the software what port addresses and what > interrupt number you will be using. I don't know; this is another of those areas where I don't know how to go about it, although I do understand what you're talking about. Don't know enough about the PC. > > 7. Unless you need more than 2 serial ports, the easiest thing to do is to > have only COM1 and COM2 in the system. > Absolutely. That much is obvious from the fact that these "overgrown" systems don't work! :-/ Unfortunately, EVERY board in there seems to want to be COM1 or COM2, with no options to "sit quietly and make nice." Thanks for the info. I await any further input. > Hope that helps. Yeah, a little. > > Venu P. Gopal > UUCP: att!ihuxy!vg55611 > Internet: vg55611@ihuxy.att.com > BITNET: com%"vg55611@ihuxy.att.com" or com%"vg55611%ihuxy@research.att.com" -- UUCP: !{iuvax,pur-ee,uunet}!bsu-cs!cfchiesa cfchiesa@bsu-cs.UUCP