Path: utzoo!attcan!utgpu!watmath!iuvax!bsu-cs!cfchiesa From: cfchiesa@bsu-cs.bsu.edu (Christopher Chiesa) Newsgroups: comp.sys.ibm.pc Subject: Hardware Weirdness with add-on boards Message-ID: <6809@bsu-cs.bsu.edu> Date: 16 Apr 89 05:23:23 GMT Organization: CS Dept, Ball St U, Muncie, IN, USA Lines: 74 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: !{iuvax,pur-ee,uunet}!bsu-cs!cfchiesa cfchiesa@bsu-cs.UUCP