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Thread: Question about ISA bus frequency

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    Default Question about ISA bus frequency

    I discovered the reason why my OPTi 929 outputs garbage out of the YMF262 every time I play the floppy disk version of Star Wars X-Wing with this sound card, and it seems the reason, according to this: http://www.oldskool.org/guides/oldonnew/sound

    Is due to the ISA bus frequency being too fast. Now, my question is this: I found this pinout of the ISA connector: http://pinouts.ru/Slots/ISA_pinout.shtml

    And I'm not sure what each arrow means. CLOCK, pin B20, has an arrow pointing right, which I'm not sure if it means input or output. Can anyone tell me what it is(I'd assume it's an output from the ISA slot to whatever device is plugged into it)? I'm positive the ISA bus frequency is too fast on my IBM Personal Computer 300PL, which is what I use for MS-DOS and Windows 95/98 gaming, as the OPTi 929 outputs a bunch of garbage notes whenever I play the floppy disk Star Wars X-Wing, but the SoundBlaster AWE64 I have that's also plugged into the computer appears to be immune to the problem, and someone who upgraded to a SoundBlaster AWE64 says he experienced no such garbled notes after upgrading his SoundBlaster AWE32 to a SoundBlaster AWE64. The only problem I have with using the AWE64 is that some notes coming from its ASIC-based YMF262 are different from a discrete YMF262, so I'd like to figure out a way to fix up my OPTi 929 to work properly with the floppy disk Star Wars X-Wing. Would I be able to remove the connection to pin B20 and solder any oscillator between 7.16 and 8MHz without causing any problems? The only thing I've been able to do to fix the problem is disable the CPU's cache, which makes the computer unbearably slow and makes Star Wars X-Wing INCREDIBLY jittery. CPU slowdown programs suck as well, so those are out of the question. So, can I just feed a 7.16 to 8MHz signal into the CLOCK pin of the OPTi 929 without any problems occurring?
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    Whuff! Outrunner Jax184's Avatar
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    I don't think the machine will be very happy with its ISA bus running out of sync with the rest of it. Can you tell us a little bit more about the specs of the machine?

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    These are its specs:

    -Intel Pentium III 500MHz
    -192MB of RAM
    -ATI Rage II graphics card
    -OPTi 929 and SoundBlaster AWE64 sound cards
    -Twin hard drives, one 5GB, the other 7GB
    -LG 52X CD-ROM drive
    -Intel 82430HX chipset on the motherboard(it's an Intel motherboard

    And I'm not talking about slowing down the ISA bus of the computer, but rather delivering a slower frequency to the OPTi 929 sound card, which freaks out and outputs garbage whenever I play the floppy disk Star Wars X-Wing without disabling the CPU's cache, and that slows down the computer A LOT. Maybe is there some way of reducing the amount of cache available without disabling it entirely?
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    YM3438 Master! ESWAT Veteran evildragon's Avatar
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    I believe if you change the frequency of the card, it'll get out of sync with the bus then, and the garbage will get worse..

    Honestly, just get an old PC.. ISA is designed to run at the old original X86 speeds (8086)..
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    I'm not doing that. This is a dual-purpose PC meant for old Windows games and MS-DOS games. I want everything in one computer, no exception. I do have an old computer with an Intel 80386, but it only has ISA slots, which means I can't use a graphics card with TV out(a necessity for video capture), and the stupid thing likes to trash every hard drive I put in it every time I try to install DOS, either by killing them completely or reformatting them to raw data.

    Would there be some way of underclocking the ISA bus speed on the motherboard? Actually, would there be some way of modifying X-Wing to slow down the speed at which the commands for the sound output are sent to the sound card?

    EDIT: I found this: http://www.pacs-portal.co.uk/Compute..._overclock.htm

    There's a chart there that indicates what's the AGP, PCI and ISA speeds depending on the speed of the FSB. My Pentium III has a 100MHz FSB, which, according to that chart, translates into ISA slots with an 8.25MHz clock(seems about right according to the chart, yet my OPTi 929 doesn't like it). CPUs with 66MHz FSB are even worse with ISA clock being 11MHz according to the chart. That should make the garbage sound worse.
    Last edited by Ace; 09-09-2010 at 09:44 PM.
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    Mastering your Systems Hero of Algol TmEE's Avatar
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    ISA should be around 8MHz in normal conditions. On my P166 machine it was 11MHz, and while my Yamaha worked perfecty, my Sound Blasters never worked nor did most other cards.
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    Whuff! Outrunner Jax184's Avatar
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    You might be able to tweak it slightly by changing the system's front side bus by a MHz or so, if the board is fancy enough to allow that. I'd suggest digging through the BIOS to see what kind of options you have for overclocking, and also try turning spread spectrum off.

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    The BIOS has no such options for overclocking/underclocking the FSB, nor does it have an option to disable spread spectrum. It seems I'm stuck with using software that can alter the FSB speed, however, I'm not sure what the clock generator is on that motherboard, which the program I'm trying to use to underclock the FSB needs to know to work(can't remember the name of the program in question).

    Here's a picture of the computer's motherboard(not my computer, but another with the exact same motherboard):


    It's an IBM 11L1619 motherboard. Anyone know what kind of clock generator this motherboard has so I can underclock the FSB?
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    To the right of that "S3" chip you have a little TSOP chip and a low-profile crystal (of 14.318MHz, probably), maybe you could replace the crystal for 12 or 13MHz ... However, that doesn't mean the ISA will slow down, it could be deriving it's clock from somewhere else

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    Whuff! Outrunner Jax184's Avatar
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    I'm curious to know why you want to stick to this particular machine. I built http://www.jax184.com/projects/K6/K6.html this guy for playing old games on for a grand total of about $40.

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    Quote Originally Posted by Jorge Nuno View Post
    To the right of that "S3" chip you have a little TSOP chip and a low-profile crystal (of 14.318MHz, probably), maybe you could replace the crystal for 12 or 13MHz ... However, that doesn't mean the ISA will slow down, it could be deriving it's clock from somewhere else
    Hey, come on, that's needed for the 14.318MHz line on all my ISA sound cards. That's not where the problem is coming from, but rather pin B20 on the ISA slot, which is NOT the 14.318MHz line for ISA cards, but a slower 8MHz line, which, on this motherboard with its 500MHz Pentium III and 100MHz FSB, appears to run at about 8.33MHz. To slow it down to 8MHz, I would need a FSB that's underclocked to about 96MHz(the ISA clock is derived from the PCI clock, which is derived from the FSB. Problem is my BIOS has no options for tweaking any speed options, so I'd need an alternative way to slow down the FSB.

    There are some dipswitches on the motherboard to adjust CPU and FSB speed. What would happen if I set the dipswitches where the FSB is 66MHz? Would the CPU be too heavily underclocked at this FSB speed or will the computer just not work?

    Quote Originally Posted by Jax184 View Post
    I'm curious to know why you want to stick to this particular machine. I built http://www.jax184.com/projects/K6/K6.html this guy for playing old games on for a grand total of about $40.
    Two reasons:

    1) My other PCs have no ISA slots
    And
    2) Those that do have ISA slots are either dead or have VIA chipsets, which cause sound problems with the floppy disk Star Wars X-Wing for MS-DOS

    I also want the computer to be powerful enough to run Star Wars X-Wing Alliance, which demands the most from a PC's hardware in the Star Wars X-Wing series. The others are much more powerful, but I can't use my OPTi 929 on them because they either have VIA chipsets with ISA slots or have no ISA slots whatsoever.

    Actually, I think the motherboards I have that supposedly don't work are not actually broken. I seem to have been using a dead Pentium III to try and get the computers to work, as that same Pentium III resulted in a constant black screen on my IBM 300PL. I think I'll give one of those motherboards a shot, as it's got a Yamaha YMF sound chip integrated on the motherboard. Should be less of a pain in the ass, and those sound chips have integrated YMF262s(I would prefer a discrete YMF262, but I'd settle for an ASIC-based YMF262 if necessary).
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    Where do you think the FSB clock comes from (maybe it's 14.318Mhz x 7 = 100.28MHz?)

    Ok, wheres what I'd do: Get a 14.318M oscillator and conected its clock to that clock line on the isa card/slot, while disconnecting the original signal.

    Get rid of the crystal near the PLL and use a slower one.

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    CPUs are usually just fine with being underclocked. Taking a 100 FSB CPU down to 66 shouldn't cause any problems, it'll just be a lot slower.

    Personally I'd grab one of the better Asus slot 1 boards that has a good amount of control/overclocking features and tweak it until it was happy.

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    Quote Originally Posted by Jorge Nuno View Post
    Where do you think the FSB clock comes from (maybe it's 14.318Mhz x 7 = 100.28MHz?)

    Ok, wheres what I'd do: Get a 14.318M oscillator and conected its clock to that clock line on the isa card/slot, while disconnecting the original signal.

    Get rid of the crystal near the PLL and use a slower one.
    Jorge, look at the ISA pinout I posted on the original post. There are TWO clock lines on the ISA slot, one of 14.318MHz, the other of about 8MHz. The 14.318MHz clock CANNOT be the culprit, as if you look at this site: http://www.oldskool.org/guides/oldonnew/sound

    It mentions a BIOS option to slow down the ISA slot's bus speed. There is NO MENTION of the 14.318MHz line.

    Actually, which of the two lines is critical to proper functioning of AdLib sound? The 14.318MHz line or the 8MHz line? If it's the 14.318MHz line, I could add a 14.318MHz oscillator to my OPTi 929, as there's a solder spot for such an oscillator on the sound card. If it's the 8MHz line, what are my options?
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    The thing is that crystal is the master crystal, most likely... Not only it generates the 14.318MHz clock for that HiSpeed clock line, but it's also used to generate the FSB clock, from which, everything else is derived including the ISA bus clock.
    Thats why I said to replace that crystal with a slower one. You'll slowdown everything (except the ISA 14.318 signal, because I said to use a specific oscillator for it).

    I doubt you can configure the PLL with software on an old OEM motherboard ...

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