ECS nForce4-A939 Voltmods

Author: celemine
Date: 2006-05-11 17:25:27

VCORE

Datasheet of the ISL6566 VCore-controller:

http://www.intersil.com/data/fn/FN9178.pdf

In general the VCore-Mod consists of two parts.

VCore-Mod (part1)

Let's start with the nearly common vmod-method of using the controller's feedback-pin to influence the output voltage. This mod requires you to connect a trimmer potentiometer between pin#9(FB) and Ground.



As you may see, I marked the appropriate points (pin#9 and ground). I advise you to use 2x 50K potentiometers connected in series for this mod. This way you get a total resitance of 100K, but with doubled precision in comparison to a single 100K poti. Now all you have to do is to connect the potentiometers just like shown in the picture. Decreasing resistance now means increasing volts.

VCore-Mod (part2)

The board is also suffering from a very annoying problem: The ISL6566's Overvoltage Protection (OVP) activates when a VCore option of about "+200mV" (might be a bit higher or lower in certain cases; official value is 175mV, according to the datasheet) is set in BIOS. Normally the controller should work in "VRM9.0"-mode, thus it should be no problem to supply a VCore of upto 375mV higher than the CPU's standard VCore. The problem now is that it operates in "AMD-HAMMER"-mode and all VCore-options above "+200mV" are quite useless, because the internal OVP gets tripped.
The ECS support told me, that due to the described problem, the VCOre-options higher than "+225mV" will be disabled in future BIOS releases (at the moment, BIOS 1.1g is the latest version).

The solution to this problem is simply influencing the CPU's standard VCore, which is generated through the 5 so called "VID-Pins". Those pins either carry a voltage higher than 1.2V or lower than this value. If the voltage is higher, it is interpreted as a logical 1 and if it's lower, it means a logical 0. The different voltages at those pins are the base of the VID-code, which consists of ones and zeros and determines the default voltage of the CPU, according to the operating mode of the voltage controller.



I marked the direct connections of the 5 VID-pins (yellow characters), the PULL-UP voltage (green characters) and one Ground point (blue characters).
As the name indicates, the pins marked as "Pull-Up" are used to pull the VID-pins up to a logical 1 ("high" status), while Ground is used to pull them down to a logical 0 ("low" status).

On page 11 (and following) of the ISL6566's datasheet, or the html-table below, you find the needed codes to know which pins to influence to get the desired default CPU voltage. The controller is configured to work in "AMD-HAMMER"-mode on this mainboard, so you have to rely on that table!
To perform this mod, the simplest and best way is to use 2x 5-position dip-switches and connect one side of either dip-switch to the VID-pins. That means pin number one of either 5-position switch to VID0, pin number 2 of the switch to VID1 and so on. Then connect the complete other row of pins (i.e. all 5 pins that are left on the opposite side) of one 5-position dip-switch to the green-marked PULL-UP voltage and finally the rest of the pins of the other 5-position dip-switch to Ground. Now you can set each VID-pin individually to either 1("high") or 0("low"). Of course, if you leave all the connections on the 2 5-position dip-switches "off" (unconnected), the CPU will still boot with its factory default voltage.

Example: The CPU has a default voltage of 1.4V. According to the "AMD-HAMMER"-table below, this corresponds to "0 0 1 1 0".
AMD HAMMER VOLTAGE IDENTIFICATION
VID4 VID3 VID2 VID1 VID0 VDAC
1 1 1 1 1 Off
1 1 1 1 0 0.800
1 1 1 0 1 0.825
1 1 1 0 0 0.850
1 1 0 1 1 0.875
1 1 0 1 0 0.900
1 1 0 0 1 0.925
1 1 0 0 0 0.950
1 0 1 1 1 0.975
1 0 1 1 0 1.000
1 0 1 0 1 1.025
1 0 1 0 0 1.050
1 0 0 1 1 1.075
1 0 0 1 0 1.100
1 0 0 0 1 1.125
1 0 0 0 0 1.150
0 1 1 1 1 1.175
0 1 1 1 0 1.200
0 1 1 0 1 1.225
0 1 1 0 0 1.250
0 1 0 1 1 1.275
0 1 0 1 0 1.300
0 1 0 0 1 1.325
0 1 0 0 0 1.350
0 0 1 1 1 1.375
0 0 1 1 0 1.400
0 0 1 0 1 1.425
0 0 1 0 0 1.450
0 0 0 1 1 1.475
0 0 0 1 0 1.500
0 0 0 0 1 1.525
0 0 0 0 0 1.550


Now let's say we want to increase the default voltage to 1.55V. In order to do so, we need to change the "1", that VID1 and VID2 are set to by default, into a "0", because the VID-Code for 1.55V is "0 0 0 0 0". All we have to do in practice is to connect VID1 and VID2 to Ground and bam, we have 1.55V VCore.
Another short example:
For a default voltage of 1.1V you would need to connect VID4 to the PULL-UP voltage and VID2 to Ground.
I hope you understand the principle.

CAUTION: Only change the VID-code using the dipswitches when the system is powered OFF and never connect any VID-pin to Ground and the PULL-UP voltage at the same time!

VCore Measure



Page:
 VDimm & VLDT »
Discuss this article in our forums