Come one, and come all; Welcome to the AMD Section. Today we're going to have a nice brief overview of what voltages are; and what all those confusing names mean. SO please join me on this ride; and add feedback as you desire. 
Down and dirty - Voltage names & what they do:
As an addition (and info thanks to Mastiffman) you can see here if you want to know what VDD & PLL Voltage stand for and exactly what they do.
Questions, Comments, or Concerns are encouraged to be left in this thread.
If you have any suggestions or voltage you would like to know about that relate to the CPU, Motherboard, or RAM Modules; please let me know and I will either answer your question directly or research it to see if I can find information on your question.
Down and dirty - Voltage names & what they do:
- VDD: This is the main CPU voltage, which can also be unofficially referred as Vcore. Usually when we say “CPU voltage” we are talking about this line. The option that changes this voltage will show up on the motherboard setup as “CPU Vcore”, “CPU Offset Voltage”, “CPU Voltage at Next Boot”, “CPU Vcore 7-Shift” and “Processor Voltage”.
- VDDNB: This is the voltage used by the CPU integrated memory controller, by the CPU HyperTransport controller and by the CPU L3 memory cache (if available). These components are collectively called “NB” or “North Bridge” by AMD. The problem is that one of the chips from the motherboard chipset can also be called “NB” or “North Bridge” and most users will get lost trying to figure out what is really being configured when an option has “NB” on it, thus we will have to explore this subject in more details. On AMD CPUs up to socket AM2 the VDD and VDDNB voltage are the same. Starting with Socket AM2+ CPUs AMD started to use separated voltages for the CPU and for the memory controller (AMD calls this “split plane” or “Dual Dynamic Power Management.")
- VDDA: This is the voltage used by the clock multiplier circuit inside the CPU, also known as PLL (Phase-Locked Loop). This voltage can be changed through options like “CPU VDDA Voltage” and “CPU PLL Voltage”, and usually only high-end motherboards have this option; it can be essential to overclocking when you use a Multiplier only approach, like what is popular with Black Edition or FX Processors in the AMD Lineup
- VDDIO: This is the voltage used by the signals on the memory bus. JEDEC (the organization that standardizes memories) calls this SSTL (Stub Series Termination Logic) voltage. This is the famous “memory voltage” configuration that can be found under several different names such as “DIMM Voltage”, “DRAM Voltage”, “Memory Over-Voltage”, “VDIMM Select”, “Memory Voltage”, etc. The default value for this line is 1.8 V with DDR2 modules (SSTL_1.8) or 1.5 V with DDR3 modules (SSTL_1.5) Though default value can vary based on the specifications of your modules. JEDEC standards are just universal standards for companies to follow.
- VTT: Voltage that is used to feed the termination logic inside the memory chips. By default it is set as half of VDDIO. Pay attention because Intel CPUs has a voltage called VTT that has a different meaning/usage. And this only applies to AMD Setups using the AM2-AM3+ platform
- MEMVREF: This is the memory reference voltage, which “configures” both the CPU and the memory module the voltage level that separates what is to be consider a “0” or a “1”, IE: voltages found on the memory bus below MEMVREF are to be considered a “0” and voltages above this level are to be considered an “1”. By default this voltage level is half of VDDIO (IE: 0.500x), but some motherboards allow you to change this ratio, usually through two options, “DRAM Ctrl Ref Voltage” (for the control lines from the memory bus; JEDEC’s official name for this voltage is VREFCA) and “DRAM Ctrl Data Ref Voltage” (for the data lines from the memory bus; JEDEC’s official name for this voltage is VREFDQ). These options are configured as a multiplier, for example “0.395x” means that the reference voltage will be 0.395 times VDDIO.
- VLDT: Voltage used by the HyperTransport links from the CPU.
- This voltage is referred as “HT Voltage”, “HT Over-Voltage”, “NB/HT Voltage” and similar names. The default value for this line is 1.2 V.
As an addition (and info thanks to Mastiffman) you can see here if you want to know what VDD & PLL Voltage stand for and exactly what they do.
Quote:
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1. VDD Stands for Voltage Drain Drain. BUT, Vdd is only a Positive (+) Supply Voltage for any Given IC of FET (Feild Effect Transistor) Circuits. Being that a Motherboards power supply to the CPU (and other areas) is "MOSFET" based or Metal Oxide Semiconductor Field Effect Transistor, the VDD Voltage only acts as a fine tuning teminal by the use of a "Drain" being that it is only a Positive Supply Terminal with Drain. If one notices, when you set the CPU Voltage on a high end Motherboard and then change the CPU VDD Voltage, the adjustment of the VDD voltage, changes the CPU Voltage, but only by .025v at a time. This is why the VDD voltages are typically looked at as the "Offset" voltage and not the vCore voltage. Normal vCore votlage will (depending on the MFR and MoBo) have larger, less accurate changes in comparison. I can leave the Vdd voltage on auto and change the Voltage of my CPU on my sig board and be stable. I may be using more voltage than i really need though. I could in fact use the Vdd adjustment to increase or decrease the CPU voltage by .025v if needed. I typically don't use it though... 2. PLL Voltage (Phase Locked Loops) is actually used to created an alternate frequency "Loop" from the CPU's, to "Lock" onto the "Phases" (in and out) of the CPU's frequency to stabilize the CPU's Frequency and to help prevent Spikes in the frequency itself, further stabilizing an OC. Typically in higher frequencies... Spikes in CPU frequency are a common reason for Computer Lock ups. Either due to an unstable setting or EMI. This is why some board come with "Spread Spectrum" settings. Areas (Cities) with abnormal amounts of Electromagnetic Interference can cause system instability in electronics. Even other electronics can cause this effect. There is no standard for adjustment of this voltage. It can only be executed properly through trial and error being that each CPU/ hardware combo is |
If you have any suggestions or voltage you would like to know about that relate to the CPU, Motherboard, or RAM Modules; please let me know and I will either answer your question directly or research it to see if I can find information on your question.
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| CPU | Motherboard | Graphics | RAM |
|---|---|---|---|
| AMD A10-A5800K | ASRock FM2A85X-ITX | Radeon HD7770 1GB | 2x8GB 1866mhz C9 |
| Hard Drive | Hard Drive | Optical Drive | Cooling |
| SanDisk Ultra Plus 128GB | 2TB 5400 RPM | 24x DVD Drive | Noctua L9A |
| OS | Monitor | Keyboard | Power |
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| Case | Mouse | Audio | |
| Cooler Master Elite 120 Advanced | Logitech K400 Trackpad | Custom 2.1 Home Theater Setup | |
| View all | |||
|
Test Bed
(24 items) |
TTTbox
(15 items) |
| CPU | Motherboard | Graphics | RAM |
|---|---|---|---|
| AMD A10-A5800K | ASRock FM2A85X-ITX | Radeon HD7770 1GB | 2x8GB 1866mhz C9 |
| Hard Drive | Hard Drive | Optical Drive | Cooling |
| SanDisk Ultra Plus 128GB | 2TB 5400 RPM | 24x DVD Drive | Noctua L9A |
| OS | Monitor | Keyboard | Power |
| Windows 7 Home Premium | 32" IPS TV | Logitech K400 | Seasonic G360 |
| Case | Mouse | Audio | |
| Cooler Master Elite 120 Advanced | Logitech K400 Trackpad | Custom 2.1 Home Theater Setup | |
| View all | |||
