Advanced Study of Accurate Voltage Measurements - Cutting Edge VCC Measuring
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Cutting Edge VCC Measuring
Another way to measure VCC is by using your Super I/O chip. In general, this I/O is a Winbond Super I/O chip sporting 8 channels to measure the voltages. It should have a total of about 128 pins. Out of those pins, each stands for something. We need to find the ones that represent the VCC. The easiest way to accomplish this is by searching for the original data sheet of your Winbond chip. It contains everything you'll ever need.
(Winbond W83697HF - 128-pin PQFP = plastic quad flat pack.)
As for searching data sheets, I'd advocate one of the following databases: Datasheet4u, Alldatasheet, DatasheetCatalog, and so forth. But almost always a quick Google works flawlessly! Just use the terms: "download data sheet fill_in_the_blanks".
In our case, download W83697_Winbond.pdf from here. Once you have it, turn to page 14 and check out the PIN configuration for this chip. Then from pages 15 up to 26 you can read each of the pins' representation. Hardware monitoring interfaces are listed on page 24. The data sheet explains their purpose, so there's no need for explanations.
(Excerpt from the official data sheet - page 14.)
Attempting this technique requires a little bit of working experience with electronics because the pins of the I/O chip are very tiny. As long as you can correctly use a DMM and accurately place the tips of needles on the correct pins, the job is done. Don't forget that you need the official data sheet because there is no way we could know intuitively the internals of a Winbond chip.
Another way of measuring VCC is possible via the VCC_SENSE and VSS_SENSE. You should download the official data sheet from Intel's website for your CPU and check the listing of "holes" at the chapter called "Land Listing and Signal Specifications." That's where you are going to find a two-page-wide land-out diagram. Those are the holes you were searching for. Then you need to find the aforementioned two lands.
Let's assume for a moment that you're running a Core2 processor. Download this data sheet. Turn to pages 48-49. The land-out diagram is located on these two pages. On page 48 you can see the left side, while on 49 is its right side; both are shown from the top view. You can see the VCC_SENSE and VSS_SENSE on the right side (page 49) on the following coordinates: AN3 and AN4, respectively (AN is the row, 3 and 4 are columns).
Once you've found where these two reside you're ready to move on. You can approach the situation using this technique if and only if you have access to the back of your motherboard. By the way, these two positions are akin to what the CPU will get to see. Therefore, this measurement workaround is the way laboratory engineers are doing it, and thus it is probably the best technique. Doing it correctly requires practice!
I'd also suggest reading chapter 2 ("Electrical Specifications") from the Intel data sheet of your processor. I am not familiar with the tidbits and data sheets of AMD and I won't comment on them. However, if you're running an Intel processor then you're no doubt lucky. Intel is doing an excellent job of publishing technical documents.
At the aforementioned chapter you can find particular information regarding VCC_Maximum, VCC_Typical, and VCC_Minimum - transient tolerance (pg. 23 for Core2s). Once you are comfortable with sticking your probes while your PC is running, you will find out firsthand how useful data sheets really are. It's just a matter of time.
Next: Final Thoughts >>
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