| 1 | VID pin settings |
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| 2 | -------------------- |
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| 3 | |
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| 4 | The VID (Voltage Identification) pins on sensor chips |
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| 5 | are used to read the CPU Core voltage setting. |
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| 6 | |
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| 7 | The VID setting can be controlled by jumpers on the board, |
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| 8 | or, in newer motherboards, by settings in the BIOS. |
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| 9 | On these newer boards, the BIOS programs some device's |
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| 10 | pins which in turn controls a DC-DC Converter to set its |
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| 11 | output to a certain voltage. These pins are also connected to |
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| 12 | the sensor chip so that the VID setting can be read back |
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| 13 | by applications. |
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| 14 | |
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| 15 | There are between 4 and 8 VID pins (the more recent the CPU, the more |
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| 16 | numerous the VID pins.) The VID codes are defined by Intel in documents |
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| 17 | titled "VRM X.X DC-DC Converter Design Guidelines". |
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| 18 | (VRM = Voltage Regulator Module), or |
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| 19 | "Voltage Regulator-Down (VRD) X.X Design Guide". |
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| 20 | These documents are available at http://developer.intel.com. |
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| 21 | There are equivalent documents for AMD processors (look for a table |
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| 22 | named "VID Code Voltages" in processor specifications.) |
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| 23 | |
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| 24 | There are several different VRM document versions. |
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| 25 | The common versions are as follows: |
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| 26 | |
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| 27 | Document Version Voltage Range Increment Processors |
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| 28 | ---------------- ------------- --------- ---------- |
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| 29 | "2.4" 0.8 - 1.55 0.025V AMD Opteron 24x |
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| 30 | |
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| 31 | 8.2 (8.1, 8.3) 1.30 - 2.05V 0.05V PII, PIII, Celeron |
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| 32 | 2.1 - 3.5V 0.10V |
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| 33 | |
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| 34 | 8.4 1.30 - 2.05V 0.05V PIII, Celeron |
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| 35 | 4 pins only |
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| 36 | |
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| 37 | 8.5 1.050 - 1.825V 0.05V PIII-S Tualatin |
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| 38 | |
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| 39 | 9.0, (9.1) 1.100 - 1.850V 0.025V P4, AMD Socket A |
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| 40 | |
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| 41 | 10.0 0.8375 - 1.6000 0.0125V Desktop Socket 478 |
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| 42 | |
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| 43 | |
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| 44 | "2.4" is not an actual document version but simply a way to identify |
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| 45 | AMD Opteron 24x processors. |
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| 46 | Note that versions 8.1 - 8.4 are compatible. |
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| 47 | |
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| 48 | Since Linux 2.6.9, the correct VRM version is selected automatically |
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| 49 | based on the CPU brand and model. Thus you shouldn't have to care about |
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| 50 | it. If you are using a brand new CPU and even the latest kernel complains |
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| 51 | ("Unknown VRM version of your CPU"), this means that the kernel must be |
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| 52 | taught about this new CPU model. Please report to us in this case. |
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| 53 | |
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| 54 | Remember, the VID pins on the sensor chips are inputs only. |
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| 55 | You cannot use them to manipulate the actual processor core voltage. |
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| 56 | |
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| 57 | ------------------ |
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| 58 | Copyright (c) 2002-2004 Mark D. Studebaker |
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