Understanding All Voltage Configurations from the Motherboard

Intel Processors – Memory Options

While all CPUs from AMD have an embedded memory controller, this is not true with models from Intel, where only the newer models (Core i3, Core i5 and Core i7) have this feature. Therefore, voltages present on the memory bus can be produced either by the CPU or by the North Bridge chip from the chipset (MCH, Memory Controller Hub), depending on the platform you have. This is why we are posting memory-related voltages on a separate page.

The memory bus requires three different voltages:

• VDDQ: 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, which can be found under several different names such as “DIMM Voltage,” “DIMM Voltage Control,” “DRAM Voltage,” “DRAM Bus Voltage,” “Memory Over-Voltage,” “VDIMM Select,” “Memory Voltage,” etc. The default value for this voltage is 1.8 V with DDR2 memories (SSTL_1.8) or 1.5 V with DDR3 memories (SSTL_1.5).
• Termination voltage: This is the voltage that is used to feed the termination logic inside the memory chips. By default, it is set at half of the VDDQ/SSTL voltage (“memory voltage”). This option, if available, will be listed as “Termination Voltage” or “DRAM Termination.” Pay attention, because this voltage with AMD CPUs is called VTT, but with Intel CPUs VTT is the processor’s secondary voltage (see previous page).
• Reference voltage: The memory reference voltage “configures” both the memory controller and the memory module with the voltage level that separates what is to be considered a “0” or a “1,” i.e., voltages found on the memory bus below the reference voltage are to be considered a “0,” and voltages above this level are to be considered a “1.” By default, this voltage level is half of the SSTL voltage (a.k.a. 0.500x), but some motherboards allow you to change this ratio, usually through options like “DDR_VREF_CA_A,” “DRAM Ctrl Ref Voltage,” and similar. “CA,” “Ctrl” and “Address” refer to the control lines from the memory bus (JEDEC’s official name for this voltage is VREFCA), while “DA” and “Data” refer to 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 the SSTL voltage. Usually, motherboards targeted to Intel processors allow you to control these voltages for each memory channel. So “DDR_VREF_CA_A” means the control reference voltage for channel A, while “DDR_VREF_CA_B” configures the control reference voltage for channel B.