alf@edstip.EDS.COM (John Hamill) (05/25/89)
I have a Joysystems 286 AT clone.
When I play some games on it I get killed right away, becouse the
clock speed is so fast (10 MHz). Im thinking of getting a 10MHz
crystal to slow the speed down to 5MHz. I think 5MHz is the speed
of an old PC. This should solve the problem of getting killed so
fast. I would like to know if I can install a switch to the two
crystals with out any problems? Will a wire running out to the back
of the computer box be too long and affect how the crystal works? Do
I need to have a switch on both leads of the crystal? Is there a way
through software to slow down the clock speed with out changing the
crystal? Any help would be helpfull.
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\/ MI 48013 davidc@vlsisj.VLSI.COM (David Chapman) (05/27/89)
In article <306@edstip.EDS.COM> alf@edstip.EDS.COM (John Hamill) writes: > >I have a Joysystems 286 AT clone. > >When I play some games on it I get killed right away, becouse the >clock speed is so fast (10 MHz). Im thinking of getting a 10MHz >crystal to slow the speed down to 5MHz. > First of all, a 5 MHz AT clone is still going to be several times (3x? 5x?) faster than a PC or XT clone. You're using a much more powerful processor. So installing a slower crystal won't help you that much. Besides, most people really want a _faster_ computer :-) > > I would like to know if I can install a switch to the two >crystals with out any problems? Will a wire running out to the back >of the computer box be too long and affect how the crystal works? Do >I need to have a switch on both leads of the crystal? Is there a way >through software to slow down the clock speed with out changing the >crystal? Any help would be helpfull. > Crystal oscillators are complex beasties (I won't touch 'em - they're _analog_ and I only know how to count to one :-). What I _do_ know is that you want the crystal leads short - it reduces the inductance. You should be able to switch in only one lead, but since DPDT switches are cheap I'd change over both of them. Make sure you don't damage the original crystal when you unsolder it! One other thing: if you do this, you should probably only change the speed while the machine is powered down. With the proper hardware, you could do the switch while the machine is running, and maybe not even require a reboot, but what you're doing is at the very least going to require that the machine be reset after a switch. Ctrl-Alt-Del won't work either - you'll need a reset button (why IBM didn't provide a reset button on a machine without protection from software errors, I'll never know). It's possible to slow the machine down in software - you write/buy/borrow (freeware) a TSR (terminate & stay resident) driver that grabs the clock interrupt and spins for a few cycles. I know there's one out there in the public domain (shareware?). Try some of the disk sellers. My own favorite (no, I don't work for them) is Public Brand Software in Indianapolis. I think they have "game slow-down" utilities on one of their disks somewhere. Their phone number was 1-800-IBM-DISK until International Business Machines complained; now it's 1-800-426-DISK (still the same, actually). They'll be happy to send you a catalog. I really think the software method will be preferable. Since the delay loop is in software, you could probably slow the machine down enough that you could start winning :-) David Chapman {known world}!decwrl!vlsisj!fndry!davidc vlsisj!fndry!davidc@decwrl.dec.com -- David Chapman {known world}!decwrl!vlsisj!fndry!davidc vlsisj!fndry!davidc@decwrl.dec.com
sparks@corpane.UUCP (John Sparks) (05/28/89)
In article <306@edstip.EDS.COM> alf@edstip.EDS.COM (John Hamill) writes: > >I have a Joysystems 286 AT clone. > >When I play some games on it I get killed right away, becouse the >clock speed is so fast (10 MHz). Im thinking of getting a 10MHz >crystal to slow the speed down to 5MHz. Hmm. Let me see if I got this right.... You are actually asking for help to *SLOW* your machine down? I thought I'd seen it all.. Now I have. :-) Standard 286 speed is 6Mhz. Maybe you can get someone to trade you for a slower machine. I don't think that you are going to be able to hook up 2 crystals and run a switch out the back. RFI problems, etc. Good luck tho. -- John Sparks | {rutgers|uunet}!ukma!corpane!sparks | D.I.S.K. 24hrs 1200bps [not for RHF] | sparks@corpane.UUCP | 502/968-5401 thru -5406 The next sentence is true. The previous sentence is false.
rdsnyder@mit-amt (Ross D. Snyder) (05/29/89)
To reduce the speed of your PC, the software hack to the operating system that someone suggested, which simply wastes clock cycles, is probably the cleanest hack. However, since this is sci.electronics, you may feel in the mood for a little digital hardware hacking, so... You could build a divider circuit based on a counter IC, such as the 74LS163, which could be inserted between the clock oscillator and the rest of the computer. With a debounced switch and the approriate logic gates, you could build a circuit that would cleanly switch between clock frequencies. You could use a thumbwheel switch to set XTAL/1, XTAL/2, XTAL/3, etc. With a clean circuit, you could probably switch anytime with no ill effects. Things to think about include: 1) Power consumption is usually a function of clock speed. 2) Dynamic RAM needs to be refreshed periodically. 3) Serial com functions require precise timing (although ususally provided by a xtal on the UART) Disclaimer: If it ain't broken, don't fix it. It's probably better to have a machine that won't let you win games than one that keeps a door from being blown shut by the wind. -Ross