A brief overview of the different voltages on your motherboard

[Johnny Bravo]

Having seen the recent buzz about PLL voltage mods and last seasons GTLREF voltage bonanza it has occurred to me that we're reaching a state where we have more control over the various different voltages on our motherboard than ever before.

I felt it necessary therefore to try and clarify some of these different voltages, maybe even supply a little explanation as to what hey do as well in the hope that we don't start mixing up our terms and getting even more confused!

at this time I'd also like to ask the community to contribute as I'm not exactly sure I've got this all right so if anything isn't 100% please make a comment and I'll rectify it accordingly


(check out my amazing Word skills! )

So I've divided the main components in to three sections; cpu, NB and DDR, I've also included arrows to represent the buses between these components, think of these as the connections between the components so that a voltage here is connected as well. We'll start from left to right.

VCORE/VCC

An easy one to start with, this is the voltage that is supplied to the billions of transistors in your cpu nothing complicated we all know where we stand here

Vdroop

This isn't so much a set voltage as an artificially induced occurrence designed into the vcore supply loop in order to make savings by allowing the designer to use higher ESR (ie cheaper) capacitors. The reason we don't like it is because it allows the vcore voltage to dip when a large current is drawn which can affect your maximum overclock. It has been included for reference but in reality is not an isolated voltage in it's on right.

VCCA (CPU PLL)

Some may have heard of this, I *think* it became popular back in the days of dothan overclocking, could be wrong. The VCCA is an isolated voltage to the cpus PLL clocks which can allow for "stiffening" of the clock signal when increased, if this is referred to in BIOSes by any other name can someone tell me please.

GTLREF

This voltage determines the reference point for the GTL+ signals. IT is tied in with the CPU VTT and FSB VTT Voltages (in fact on several boards the BIOS option is given as a % or decimal multiplier like 63% or 0.63 - this is based on the ratio of CPU VTT/FSB Voltage which Intel specifies as 0.63 as standard) I've associated it here with the CPU rather than the bus but it is rather difficult to isolate in this regard

VTT (CPU)/VCCIOPLL

VCCIOPLL is another isolated voltage on the cpu but this time it controls the FSB PLL clocks hence its association with this bus. It has usually been referred to as simply "VTT" in most cases but this term will need better clarification in future as there are many VTT (voltage termination) signals on a motherboard. This VTT signal is from the cpus perspective rather than from the perspective of the northbridge. Most Motherboard manufacturers will have this labeled as "CPU VTT", I can't think of any who don't.

VCCPLL

VCCPLL appears to have superseded VCCA and VCCIOPLL and is implemented on the core2duo cpu package. It is a "new" pin in that it's not a renaming of either VCCA or VCCIOPLL but the reallocation of a possibly dormant pin. Documented as providing isolated power for internal processor FSB PLLs it would seem that it has taken over the duties of the VCCIOPLL which is no longer given a listing in the documentation.

VTT (FSB)/VFSB

This is where things can get a little messy. The termination voltage mentioned above can also be adjusted from the perspective of the northbridge. I've listed it as VTT(FSB)/VSB but I'm sure they may be other names out there for it (anyone?). What I have seen is people grouping VFSB and VCCIOPLL together like they were the same. This is not the case, it is possible to have two different mods for this termination voltage as the termination happens at both ends of the bus.

Vnb/Vmch

This on is pretty straight forward, main supply voltage to the NB it's name can change sometimes change between NB, mch (memory controller hub), and even on the rare occasion spp (system platform processor) depending on your choice of platform.

VTT (DDR)

The same as the other termination voltages, this time its for the system memory. I'd hazard a guess that this was the first of the termination voltages to be modded for manual adjustment.

Vddr(2/3)

Vddr; no surprises here, this is the voltage that your memory runs at.

VPLL (Clockgen Voltage)

I've left this outside the system as this isn't strictly to do with any of the system. This is the voltage that the clockgen VCC runs off, and it has been shown that increasing it can help with your overclocks, no doubt by stiffening the clock signal sent from it. DFI list this as the clockgen voltage, Asus list it as the PLL voltage (though it could also refer to the voltage regulator, I needs some clarification on this one) and I'm gonna guess other people will call it other things too

For those in the know I'd like the ones in red to be clarified as I'm unsure if they are strictly correct - any input is welcome

[hvtecgr]

Geat guide!!!it is very usefull to understand what your doing!

[celemine1Gig]

Hmm, a very interesting read for sure.

Just one thing: I'm not sure if VCCA is the real deal for todays Core2 Duo and Core2 Quad CPUs.
VCCA isn't even explicitly mentioned in the Core2 Quad datasheet. But, Vccpll is.

VCCPLL - Input - VCCPLL provides isolated power for internal processor FSB PLLs.

I'm not 100% sure, just one thing that I noticed today.

[bassie]

Nice guide

[Johnny Bravo]

Hmm, a very interesting read for sure.

Just one thing: I'm not sure if VCCA is the real deal for todays Core2 Duo and Core2 Quad CPUs.
VCCA isn't even explicitly mentioned in the Core2 Quad datasheet. But, Vccpll is.


I'm not 100% sure, just one thing that I noticed today.

thanks celemine1Gig, perhaps it's a name change if VCCA is no longer named, as VCCPLL would seem to reference the same voltages?

The VCCA reference was taken from an older white paper from the Cedar Mill generation. I will make amendments

[celemine1Gig]

thanks celemine1Gig, perhaps it's a name change if VCCA is no longer named, as VCCPLL would seem to reference the same voltages?

The VCCA reference was taken from an older white paper from the Cedar Mill generation. I will make amendments

The land-name "VCCA" is still present, on processor-land A23 (Edit: Just checked, it is not B23, but A23, as corrected), if I'm not mistaking. Right under (Edit: B23 "VSSA") C23 "VCCIOPLL", which again is located directly under D23 "VCCPLL". The thing is that absolutely nothing is mentioned about "VCCA", while there is the quote about "VCCPLL" and the matching electrical specs for it.

[Johnny Bravo]

It would seem that on the older cpus there were two on board pll circuits one for the core (VCCA) and one for the FSB (VCCIOPLL). On the C2D this would appear to have been reduced to a single input (VCCPLL).

Looking at the white papers for the core2duo and the Pentium D I have noticed a few things in regards to these voltage inputs:

1. VCCA and VCCIOPLL pins are static across both packages
2. The documented use of this pins is not noted for some reason on the c2d white sheet (perhaps because they have no use?)
3. The VCCPLL pin (D23) is referenced as FC9 on the older cpus - and is documented as an output rather than input
4. The VCCPLL is documented as the voltage supply for the FSB PLL (perhaps the need for the cpu pll supply voltage has gone?)

As such I think it's still prudent to keep the separate references up but I will include VCCPLL as a separate entity for current cpus

[celemine1Gig]

..
As such I think it's still prudent to keep the separate references up but I will include VCCPLL as a separate entity for current cpus

I fully agree. That is most likely the best idea.

[bassie]

Any updates?

[Machinus]

Thank You!!!

[Nuckin_Futs]

K, getting it so far. So for my system rgith now, an ASUS MAXIMUS FORMULA SE w/ E6750, I get only the CPU PLL, FSBT, CPU GTL, NB GTL, DDR Controller GTL, DDR A & B GTL REF. Asside from rAm for now, what order of tweaking should I start with first to get a 4GHz stable and know if it's my temps or CPU holding me back. I get 68c on 2 cores in Prime95 v24.4 for 37min in case with fans high and door open and 20c room (24c neer/around case).

Right now I'm @

CPU: 1.56v
CPU PLL: 1.640v
NB: 1.50v
FSBT: 1.50v
DRAM: 2.24v as DDR1000 5-5-5-15 for test (good @ 4-4-4-9 @ 2.275v
CPU & NB GTL REF each @ 63x
DRAM REF: 1.14v
SB: 1.10v
SB 1.5: 1.58v

My PSU rails are @ 3.2v, 4.87v, @ 12.32v under load. Is this suitable with a 4 disc RAID set, 2 DVD & single GPU: 7950GTX, Audio: Audigy 2 ZS Plat Pro?

[hawtrawkr]

thank you for this great post will help me out quite a bit.+ always got confused by all the diffrent vtt listings on mobo this helps to clarify alot of that for me now.