BG> Keith, at 11:09 on Jul 29 1996, you wrote to Bill Grimsley...

KR> well i've given up, there seems no way that an amd5x86-133 will run with
KR> my motherboard. i've tried all combinations that i can think of, but it
KR> still hangs on boot with the chip set to a quadrupler. set to a tripler,
KR> it runs as you would expect exactly at the speed of a dx-100. i stiil
KR> dont see why, when a multiplier chip, afaik, should look just like a
KR> dx-33 externally. ah well such is life. ):

 BG> On boards which do not specifically support the 5x86, the CPU will (or
 BG> should) still run as a tripler, as long as your board is jumpered for
 BG> an AMD DX4/100.  Later boards mention the AMD Enhanced CPU, and SOME
 BG> of these handle the 5x86 as a quadrupler, as long as there is a jumper
 BG> which physically switches the CLKMUL pin of the CPU socket to a low
 BG> state (i.e. shorts it to the Vss plane). 

 BG> Pin 17 of the 5x86 is the CLKMUL (Clock Multiplier), and if left
 BG> floating (or high), the chip runs as a doubler or tripler (not exactly
 BG> clear from the AMD docs for the 5x86, but this depends on other
 BG> jumpered inputs).  However, when physically pulled low, the CPU will
 BG> run at 4x CLK, even on boards which don't support this chip or mode.

i dont think that i have a problem getting it to quadruple, there is one
link on the mb which put in one position causes the 5x86 to give identical
performance to a dx4-100 (its doing it now to produce this). if i move it
to the other position (it's function is not explained in the mb manual) the
whole thing collapses, and locks on boot. using a dx4-100 the same
positions make it run at 66mhz and 100mhz respectively. the problem is just
that the rest of the board cant take the strain of the cpu running at
133mhz.

KR> ps. i tried another motherboard of identical model, jumpered as far as i
KR> could tell exactly the same. it still hung in exactly the same way with
KR> the chip set as a quad, but with it set as a tripler, it gave a landmark
KR> of 270 instead of 475 with my motherboard ??????

 BG> Randall has the AMD doco for the 5x86 (it's around 2Mb I believe),
 BG> which is necessary to figure out which is pin 17, and also which are
 BG> the Vss pins (around 25-odd in all), and the idea is to use a tiny bit
 BG> of wire on the CPU itself, before mounting it in its socket, to short
 BG> pin 17 to the nearest Vss pin (makes it semi-permanent though).  The
 BG> CPU will then run as a quadrupler, although the BIOS will generally
 BG> report something different, as it knows fuck all about quadruplers.

 BG> Randall tried this on the weekend, and although the BIOS said it was
 BG> an AMD 486DX2-130 (must be as high as that particluar BIOS
 BG> recognised), Landmark proved that it was indeed running as a 4x
 BG> {at}160MHz (and reliably so as well).  If you want to try this yourself,
 BG> I'd suggest you drop Randall Lane a message in either Z3_Tech or
 BG> Oz_Modems (that should please Ian no end :)) and ask him for further
 BG> details (like how to recognise pin 17, for a start).

like i said, i dont think that this is my problem, i think that the chip is
running at 133mhz internally, its just that everything locks up either just
after the post (i suspect the aha2842) or when the system box is displayed.

 BG> The bottom line is that we think the 5x86 can be made to run as a
 BG> quadrupler on the vast majority of 486 boards which also support AMD
 BG> DX2 or DX4 CPUs, and at just $60 ex tax for the chip, that makes them
 BG> great value IMO.

i'd agree that it is great value if i could just get the thing to run, i'd
buy a new motherboard for $120 that i know will work, but that would mean
getting a new video, and scsi board coz the mb is pci. ):

                keith
@EOT:

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