First post, by Sphere478
Sphere's PCB projects.
This one is as small as it gets and only for setting multipliers.
Designed to go on the back of the motherboard but also to be as minimalistic as possible
Here is the first beta. someone will have to prototype it to confirm it doesn't need any alterations. (At one's own risk of course.)
The Tweaker is in parallel with whatever signals the motherboard has present. If you already have a pull up present (2.2k) on a particular BF pin there is no need to install it on the tweaker. If you want to disable a pull down you must remove the motherboard jumper for that BF signal as well as turn off the dip for that pin in both locations.
You can fully set all BF registers from the Tweaker, or use a combination of the Tweaker and the jumpers on the front of the motherboard.
For example, if your motherboard can set BF0, and BF1 just fine, but can not set BF2 you could choose to leave Bf0, BF1 unpopulated on the tweaker (or off), and only use the tweaker for setting BF2
If your motherboard is missing pull up signals you can use the Tweaker for adding them.
For example, it is common to be missing a pull up on BF1 and Tillamook BF2. to discover if a pull up is present, remove processor, remove pull down jumpers, and Turn off DIPs. Then look for resistance between the specific BF pin and vcc3
The furthest DIP switch from the pins is for disabling or enabling the Tillamook BF2 pin connection. keep it disabled if no Tillamook is installed. it is known that cyrix uses this pin for other functions.
A guide to what settings give which multipliers would be very difficult to make as sometimes for example the same setting on the same S-Spec intel cpus can give different results depending on the chip. therefore it's just best to figure out which combos do what by trial and error.
This should help though:
There are four BF pins:
-BF2 (Cyrix/ST/IBM/AMD/Winchip) from here forward I will just refer to it as BF2
-BF2 (Intel Tillamook) from here forward It will be specified that it is the intel/Tillamook BF2
Yep, that's not a typo. There are indeed two pins called BF2 the Intel one at some point was going to become the new standard it seems because it ended up on the Tillamook and some desktop motherboards even routed a jumper to it. But something happened and it never caught on. Instead the various super socket 7 processors ended up using a different pin for BF2 and Cyrix even used Intel's BF2 pin for another function. which is why there is a switch to disconnect it on this PCB. Be sure to only switch it on for Tillamook cpus.
early chips I believe only used BF0 and BF1. later cyrix chips used BF0, BF1, and BF2.
Some late winchips made use of BF0, BF1 and BF2
Refer to Cyrix (Same chip, different label)
Refer to Cyrix (Same chip, different label)
Rise cpus only ever used Bf0 and BF1 as far as I am aware.
Intel only ever used BF0, and Bf1 on their desktop CPUs. The Tillamook Pentium MMX mobile however, began using a "special" BF2 pin that is different from the AMD/Cyrix BF2 pin. (Tillamook/Intel BF2)
AMD used BF0 and BF1 early on and added BF2 later on
There are a lot of different multipliers that can be set on socket 5/7/SS7 CPUs ranging from 1x all the way to 6x with many fractional or non whole number multipliers in there as well. These multipliers, are set inside the CPU and the only thing you can do to select them is through these four registers, The one exception to this is the very last SS7 cpus to be released, the legendary k6-2+ and k6-3+ CPUs added the ability to alter multipliers via software.
The CPU must internally support the multiplier you are trying to set though. For example: you simply can not set 1x on a K6 or 6X on a K5 no matter how hard you try. the CPU must internally support the multiplier.
Re: Cyrix 400gp multiplier settings
Re: Rise cpu voltage and mhz settings
Idt Winchip 1, 2, 2a and 2b differences
Examples of some digging into the supported multipliers of some different chips.^
Cyrix/IBM/ST CPUS seem to have the distinction of some of them supporting a 4x and some a 1x multiplier
Some Tillamooks (266mhz) have a 4x multiplier and a 4.5x multiplier is rumored to be present on 300mhz chips.
Pentium mmx p55c supports up to 3.5x via the typical 1.5x setting.
Many pentium MMX chips got their multipliers scrambled by intel. As mentioned before sometimes several specimens with the same s-spec number can give different results on the same BF setting. Many are locked out of multipliers above their rating but some have all unlocked.
Rise cpus that I have tried support up to 3.5x
On late model K6 CPUS they re mapped the 2x setting to 6x allowing users to install them into 66-83mhz FSB motherboards (including ones that didn't have BF2) and run them at respectable clock rates of 400-500 mhz. (Because the 2x setting uses only BF0 and BF1)
Winchip: Supposedly some Winchips supported up to 5x..?