ong@d.cs.okstate.edu (ONG ENG TENG) (01/05/91)
As I mentioned before, just got a 16MHz 386SX. In the manual, it seems to be saying that the same motherboard (merely refered to as NEATsx motherboard, manual prepared by a technical documentation company) can be used as a 16MHz or 20MHz. Can it be true that I merely has to change the CPU from a 386SX-16 to a 386SX-20 and speed the RAM up appropriately, add the 40MHz oscillator (for the 20MHz CPU, as mentioned in the manual), and I have a 20MHz 386SX. Does anyone has any actual or near-actual knowledge about this? Or even educated speculations? Does anyone know the price of a 386SX-20 off the market? How about trading-in the 386SX-16? I have seen price for some motherboard selling without CPU, but no price for the CPU itself. Thanks in advance. E. Teng Ong (ong@d.cs.okstate.edu)
silver@xrtll.uucp (Hi Ho Silver) (01/06/91)
It likely depends on the design of your motherboard. There are several parts which are speed-sensitive: - the 386SX; as you propose to replace this with a 20 MHz part, this isn't a problem - the chipset; as yours claims to work up to 20 MHz, this isn't a problem either - the memory; I believe you were considering upgrading this as well. - the expansion (ISA) bus. The standard for this bus is 8 MHz. Many (most?) cards will reliably run faster than this, but some won't. If the bus is driven from the same crystal as your CPU (it might or might not be, depending on the whims of the motherboard designers), then going to 20 MHz would increase your bus rate to 10 MHz, and may or may not cause problems. - the board design; chances are everything else will run OK at 20 MHz, but it isn't necessarily guaranteed. Also, increasing your clock speed may affect radio emissions from your box. This may or may not be a concern for you. -- __ __ _ | ...!nexus.yorku.edu!xrtll!silver | always (__ | | | | |_ |_) >----------------------------------< searching __) | |_ \/ |__ | \ | if you don't like my posts, type | for _____________________/ find / -print|xargs cat|compress | SNTF
ong@d.cs.okstate.edu (ONG ENG TENG) (01/06/91)
From article <1991Jan5.040434.15650@d.cs.okstate.edu>, by ong@d.cs.okstate.edu (ONG ENG TENG): > As I mentioned before, just got a 16MHz 386SX. In the manual, it seems > to be saying that the same motherboard (merely refered to as NEATsx > motherboard, manual prepared by a technical documentation company) can > be used as a 16MHz or 20MHz. Can it be true that I merely has to > change the CPU from a 386SX-16 to a 386SX-20 and speed the RAM > up appropriately, add the 40MHz oscillator (for the 20MHz CPU, as > mentioned in the manual), and I have a 20MHz 386SX. Does anyone > has any actual or near-actual knowledge about this? Or even > educated speculations? > > Does anyone know the price of a 386SX-20 off the market? How about > trading-in the 386SX-16? I have seen price for some motherboard > selling without CPU, but no price for the CPU itself. Since I got a few e-mails that need followups and also request to post the result, I am posting this. I was told thru email that I properly couldn't do it since most 386SX CPU are soldered onto the motherboard (I looked and mine is). My question is, is there any remote possibility that the 386SX-16 will run at 20MHz. The memory on the motherboard is ready to run at that speed and my only investment will be the 40MHz oscillator (to run the CPU at 20MHz), unless of course that might cause some permanent damage to the motherboard upon failing. Thanks in advance. > E. Teng Ong (ong@d.cs.okstate.edu)
silver@xrtll.uucp (Hi Ho Silver) (01/07/91)
In comp.sys.ibm.pc.hardware, ong@d.cs.okstate.edu wrote: $My question is, is there any remote possibility that the 386SX-16 $will run at 20MHz. The memory on the motherboard is ready to run at There is a possibility, yes, but I don't know how remote it is. The way most speed-sensitive chips are produced is in one batch. They set a quota of how many high-speed parts are needed and then they test each chip from the batch at that speed. Those which pass are marked for high speed operation; those which fail are marked for low speed. But once they have their quota, the rest are not tested at high speed and are simply marked as low speed. As I said, that's the common method; there's no guarantee that it applies to the 386SX. Assuming the 386SX is produced in that manner, you could have a chip that failed the test, or you could have one that's never been tested. Do you want to roll the dice? Chances are pretty good that you won't damage anything if your chip won't run at the higher speed, although the higher the speed, the more heat is generated, so you'll want to make sure you have _lots_ of air movement. You could cause a chip to fail if it runs too hot; you'll certainly reduce its life expectancy. -- __ __ _ | ...!nexus.yorku.edu!xrtll!silver | always (__ | | | | |_ |_) >----------------------------------< searching __) | |_ \/ |__ | \ | if you don't like my posts, type | for _____________________/ find / -print|xargs cat|compress | SNTF
mlord@bwdls58.bnr.ca (Mark Lord) (01/08/91)
In article <1991Jan5.192547.20804@d.cs.okstate.edu> ong@d.cs.okstate.edu (ONG ENG TENG) writes: < <My question is, is there any remote possibility that the 386SX-16 <will run at 20MHz. The memory on the motherboard is ready to run at <that speed and my only investment will be the 40MHz oscillator (to <run the CPU at 20MHz), unless of course that might cause some <permanent damage to the motherboard upon failing. My 386sx is running at 18Mhz with a heavy heatsink. Failed the 20Mhz test, but works just fine at 18Mhz. -- ___Mark S. Lord__________________________________________ | ..uunet!bnrgate!mlord%bmerh724 | Climb Free Or Die (NH) | | MLORD@BNR.CA Ottawa, Ontario | Personal views only. | |________________________________|________________________|
ong@d.cs.okstate.edu (ONG ENG TENG) (01/08/91)
Well, folks, looks like I am gonna plunge head-first into this speedup 16-to-20 deal. Since I already have DRAM fast enough for 20MHz operations and has been informed (no I won't hold you to it!) that 386SX-16 can very well run at 20MHz, the only thing I need is the optional 40MHz oscillator (for the 20MHz operation). I have found 2 sources for them: at JDR Microdevice catalog (whom I deal with from time to time for both PC cards and I.C., etc) with the description of Oscillators part# OSC40.0 at 40.0MHz, casing type of OSC ($4.95). The only problem is that they did not display a picture of OSC casing. The type of casing on the optional oscillator slot into the PC is kind of like a 8-pin I.C. BUT with rounded pins that are NOT pertruding outsider the length or width of the casing (but rather only downwards). The other source is Digi-key with whom I only dealed with once (service great but price? Hmmm...). They have 2 items which might go into my PC the first being a Full Range Quartz Crystall Oscillator part# X120 at 40.0000MHz ($4.26) and Clock Oscillator part# CTX12040.000MHz ($4.40). Both have the diagram of the casing and it seems both will fit into the PC optional oscillator slot. Anyone has any idea which one I should go with? Thanks in advance. E. Teng Ong (ong@d.cs.okstate.edu)
ong@d.cs.okstate.edu (ONG ENG TENG) (01/08/91)
From article <5173@bwdls58.UUCP>, by mlord@bwdls58.bnr.ca (Mark Lord): > My 386sx is running at 18Mhz with a heavy heatsink. Failed the 20Mhz test, > but works just fine at 18Mhz. Ok, ok. I say I was going to plunge head-first and speed my 16MHz motherboard up to 20MHz. But now, come to think of it, heat might be a problem. Yes, big problem, like CPU burning? Anyone has any idea? Thanks in advance. E. Teng Ong (ong@d.cs.okstate.edu) P.s. You bet I am gonna wait!
rcollins@altos86.Altos.COM (Robert Collins) (01/16/91)
In article <1991Jan5.192547.20804@d.cs.okstate.edu> ong@d.cs.okstate.edu (ONG ENG TENG) writes: >> As I mentioned before, just got a 16MHz 386SX. In the manual, it seems >> to be saying that the same motherboard (merely refered to as NEATsx >> motherboard, manual prepared by a technical documentation company) can >> be used as a 16MHz or 20MHz. Can it be true that I merely has to >> change the CPU from a 386SX-16 to a 386SX-20 and speed the RAM >> up appropriately, add the 40MHz oscillator (for the 20MHz CPU, as The hardware probably will handle it, but the real question is will the peripheral bus handle it? The NEAT chipset can drive the bus in two different manners: 1) it can run syncronously to the system clock as SYS_CLOCK / 2, SYS_CLOCK / 3, etc. or 2) it can run asyncronously from a separate clock crystal. If your computer runs the bus asyncronously, then you have it made in the shade. If it is syncronous, then you must change the BIOS to program the NEAT for a different BCLOCK divisor. If you don't reprogram the chipset for the correct value, then your peripheral bus will run too fast, and some plug-in cards might not work. Now, you need to find the location in the BIOS that programs the chipset. Here is how you can find it: 1) Get yourself an 80386-SX ICE ($15,000 - $20,000), or rent one. 2) Hook up your SX to the ICE (you must desolder the SX for this) 3) Determine which chipset register programs the BCLOCK divisor, and issue this ICE command (assuming REG_NUM = BCLOCK register): GO TIL STATUS 1011110y at 20p is 0xxREG_NUMxxxx 4) The ICE will halt when port 22h = REG_NUM. Write down where the BIOS is in its code, and where it got its data. 5) Make a binary image of the BIOS, and modify the data in the binary image to the correct BCLOCK divisor. 6) Recompute the checksum on the BIOS, and burn a (set of) EPROM(s). That's all there is to it...but it can be done! -- "Worship the Lord your God, and serve him only." Mat. 4:10 Robert Collins UUCP: ...!sun!altos86!rcollins HOME: (408) 225-8002 WORK: (408) 432-6200 x4356
ong@d.cs.okstate.edu (ONG ENG TENG) (01/16/91)
From article <4610@altos86.Altos.COM>, by rcollins@altos86.Altos.COM (Robert Collins): > In article <1991Jan5.192547.20804@d.cs.okstate.edu> ong@d.cs.okstate.edu (ONG ENG TENG) writes: >>> As I mentioned before, just got a 16MHz 386SX. In the manual, it seems >>> to be saying that the same motherboard (merely refered to as NEATsx >>> motherboard, manual prepared by a technical documentation company) can >>> be used as a 16MHz or 20MHz. Can it be true that I merely has to >>> change the CPU from a 386SX-16 to a 386SX-20 and speed the RAM >>> up appropriately, add the 40MHz oscillator (for the 20MHz CPU, as > > The hardware probably will handle it, but the real question is will the > peripheral bus handle it? The NEAT chipset can drive the bus in two > different manners: 1) it can run syncronously to the system clock as > SYS_CLOCK / 2, SYS_CLOCK / 3, etc. or 2) it can run asyncronously > from a separate clock crystal. If your computer runs the bus > asyncronously, then you have it made in the shade. Hhhmmm... I thought the discussion ended two centuries ago. Well, my NEATsx chipset motherboard allows use of an optional crystal for 20MHz operation. This is set via a shorting block on the MB. My only concern now is the heat. Well, since we are here, I might as well make an update since I got help from so many people, some of whom themselves are interested in doing the same. I have ordered 3 crystal oscillators from Digi-Key few days ago. One 35Mhz (for 17.5MHz operation) and two 40MHz (for 20MHz operations) of different casing (I don't know which will fit). I also ordered a good-size heatsink, but they no longer carry any heat-resistant glue. Hopefully the local Radioshack carries some else I am up the creek w/o a paddle. (Anyone care to send me some, I promise not to sue if my motherboard blows up, ha, ha). Another would be that the MB and CPU is actually built for 20MHz operation and that heatsink is not needed. Let you know after the surgery. E. Teng Ong (ong@d.cs.okstate.edu)