cfchiesa@bsu-cs.bsu.edu (Christopher Chiesa) (04/16/89)
Greetings... I am not normally a PC user, hacker, or devotee, but through a
strange series of circumstances have found myself poking about in the guts of
two VERY "separate and distinct" PC-clone systems in the past week, trying to
diagnose "non-working hardware" problems and coming to almost identical conclu-
sions despite relatively large differences (my opinion) in the two systems.
Both "PCs" (Please allow me to call them that, even though they're clones?)
have been configured with third-party boards plugged into the internal expan-
sion slots; both appear to be clones of either an "AT" or "XT" (I don't know
what the distinction is), with a hard drive and a single floppy drive. One
is trying to use a "Practical Peripherals" internal modem, the other is trying
to use a couple of boards that together are supposed to perform interactive
video for instructional use -- the intent is to overlay PC graphics and
laserdisk video, and have the PC able to tell the laser disk what frame to
play, freeze, display, etc. etc. etc., "on the fly" under software control.
The only other thing these two systems have in common is that they DON'T
WORK, and that the problem appears to be due to something else "stealing" the
COM2 port signals!
The first system's trouble manifests in the strange fact that you can run
a terminal program and send commands to the modem, and have it obey them --
proving that data is getting FROM the PC circuitry TO the modem -- but that
NOTHING -- modem response codes, modem internal-data-echo, remote host data
-- makes it BACK TO the PC circuitry FROM the modem, for display. At first
I thought the modem was simply flaky, but then I noticed another board in
a nearby slot, driving two "serial ports." It seemed unlikely that the PC
could properly drive THOSE serial ports and still drive the modem on COM1
or COM2 as it was doing. I powered down, removed that serial-port card,
booted back up, and VOILA! Perfect performance from the modem. Somehow,
that other card "steals" or "masks out" whatever signals are trying to
send data in from the modem. Unfortunately, the serial-port card has also
the responsibility for a PARALLEL port, to which the system's PRINTER is
attached, so must remain in the system. My questions on this are obvious:
is there any reasonable way to let these cards coexist in the system and
BOTH work? No use is made of the two "jamming" serial ports, but even
when dip switches are set to "disable" both of them, the modem signals
are still blanked.
The second system, the interactive-video thing, actually works fine EXCEPT
that the PC fails to command the Laser Disk properly. This problem is less
well-defined, since there's no real proof yet that the Laser Disk player
actually would respond to commands even if they GOT to it. But on the assump-
tion that if commands GOT there, they'd command the player, the problem appears
to be that the commands just aren't getting out. On this one, I actually
phoned the manufacturer (in Colorado; I am in New York (forget the Indiana
username here...)) and verified that the driver software was in the right
place on the disk, CONFIG.SYS had the proper line in it, and the DIP switches
on the Laser Disk player were set properly. The circuit boards involved in
this system, again, have "COM2" involvement, and that day's session with the
manufacturer ended with his surmise that "... maybe there's a serial COM2
port built into the main board on that PC clone, and it is STEALING INTERRUPT
THREE..."
"Stealing interrupt three!" Sounds like he knows more about the PC than I
do, but maybe less than someone reading these words! If someone here can
suggest anything I haven't tried, or a way to verify or disprove this diag-
nosis, I'd sure appreciate hearing it. The lady with the modem may be
forced to yank circuit boards every time she wants to use it, and the people
with the video system may have several thousand bucks worth of "white ele-
phant" on their hands, without your help.
Thanks in advance... by the way, I'm not only not a REGULAR reader of this
group, I've never read it at ALL til now. Please respond via email so I'll
SEE the response.
Chris Chiesa
former Ball State Student
Now trying to render assistance in the Real World
--
UUCP: <backbones>!{iuvax,pur-ee,uunet}!bsu-cs!cfchiesa
cfchiesa@bsu-cs.UUCP vg55611@ihuxy.ATT.COM (Gopal) (04/17/89)
In article <6809@bsu-cs.bsu.edu> cfchiesa@bsu-cs.bsu.edu (Christopher Chiesa) writes: {stuff deleted} >Both "PCs" (Please allow me to call them that, even though they're clones?) >have been configured with third-party boards plugged into the internal expan- >sion slots; both appear to be clones of either an "AT" or "XT" (I don't know >what the distinction is), with a hard drive and a single floppy drive. One >is trying to use a "Practical Peripherals" internal modem, the other is trying >to use a couple of boards that together are supposed to perform interactive >video for instructional use -- the intent is to overlay PC graphics and >laserdisk video, and have the PC able to tell the laser disk what frame to >play, freeze, display, etc. etc. etc., "on the fly" under software control. >The only other thing these two systems have in common is that they DON'T >WORK, and that the problem appears to be due to something else "stealing" the >COM2 port signals! >The first system's trouble manifests in the strange fact that you can run >a terminal program and send commands to the modem, and have it obey them -- >proving that data is getting FROM the PC circuitry TO the modem -- but that >NOTHING -- modem response codes, modem internal-data-echo, remote host data >-- makes it BACK TO the PC circuitry FROM the modem, for display. At first >I thought the modem was simply flaky, but then I noticed another board in >a nearby slot, driving two "serial ports." It seemed unlikely that the PC >could properly drive THOSE serial ports and still drive the modem on COM1 >or COM2 as it was doing. I powered down, removed that serial-port card, >booted back up, and VOILA! Perfect performance from the modem. Somehow, >that other card "steals" or "masks out" whatever signals are trying to >send data in from the modem. Unfortunately, the serial-port card has also >the responsibility for a PARALLEL port, to which the system's PRINTER is >attached, so must remain in the system. My questions on this are obvious: >is there any reasonable way to let these cards coexist in the system and >BOTH work? No use is made of the two "jamming" serial ports, but even >when dip switches are set to "disable" both of them, the modem signals >are still blanked. >The second system, the interactive-video thing, actually works fine EXCEPT >that the PC fails to command the Laser Disk properly. This problem is less >well-defined, since there's no real proof yet that the Laser Disk player >actually would respond to commands even if they GOT to it. But on the assump- >tion that if commands GOT there, they'd command the player, the problem appears >to be that the commands just aren't getting out. On this one, I actually >phoned the manufacturer (in Colorado; I am in New York (forget the Indiana >username here...)) and verified that the driver software was in the right >place on the disk, CONFIG.SYS had the proper line in it, and the DIP switches >on the Laser Disk player were set properly. The circuit boards involved in >this system, again, have "COM2" involvement, and that day's session with the >manufacturer ended with his surmise that "... maybe there's a serial COM2 >port built into the main board on that PC clone, and it is STEALING INTERRUPT >THREE..." {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.. 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. 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. 4. If you have add-on serial ports, ensure that they are at different port addresses from the built-in ones. 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. 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. 7. Unless you need more than 2 serial ports, the easiest thing to do is to have only COM1 and COM2 in the system. Hope that helps. 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" Silence those silent letters and save the world 500 million keystrokes a day.
cfchiesa@bsu-cs.bsu.edu (Christopher Chiesa) (04/18/89)
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: <backbones>!{iuvax,pur-ee,uunet}!bsu-cs!cfchiesa cfchiesa@bsu-cs.UUCP
silver@eniac.seas.upenn.edu (Andy Silverman) (04/18/89)
In reference to the previous postings trying to resolve conflicts between serial ports, it should be noted that not only serial cards should be checked for these potential conflicts. For example, my Microsoft Bus Mouse card can use any of several hardware interrupts, two of them being the interrupts usually used by the COM ports. In my case, I had no choice but to use this setting since all the other alternatives were taken up by my HD controller, EGA card, etc. The point here is that other cards which use the COM port interrupts for their own purposes may be causing the problem. +----------------+-----------------------------------------+ | Andy Silverman | Internet: silver@eniac.seas.upenn.edu | | "Why?" | Compu$erve: 72261,531 | +----------------+-----------------------------------------+