Abstract:
A motherboard may be adapted to selectively implement one of two different memory technologies. For example, the motherboard may be able to subsequently implement a subsequently developed memory technology. In some embodiments, the motherboard is capable of detecting whether a memory module is in a slot dedicated to a first or a second memory technology and, based on the presence of a memory module in an appropriate slot, the motherboard may be adapted to operate with the particular, selected memory technology.

Description:
BACKGROUND  
       [0001]    This relates generally to motherboards used in processor-based systems. 
         [0002]    A motherboard may provide basic components of a computer system, including a processor and memory. Currently, many motherboards include the double data rate two synchronous dynamic random access memory (DDR2 SDRAM) on board. The DDR2 memory comes in particular package types and particular densities. Generally, the DDR2 memories have a maximum density of 4 gigabytes. They have data rates from 400 to 1066 megabytes per second, per pin. They have supply voltages of about 1.8 volts and have specific packaging types. Thus, a motherboard adapted for DDR2 memories generally is not amenable to handling other memory technologies. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0003]      FIG. 1  is a circuit schematic for one embodiment of the present invention; and 
           [0004]      FIG. 2  is a flow chart for the embodiment shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION  
       [0005]    In accordance with one embodiment of the present invention, a motherboard  10 , shown in  FIG. 1 , may be adaptable to selectively implementing one of at least two different memory technologies. For example, the motherboard  10  may implement a double data rate synchronous dynamic random access memory (SDRAM) that is either of the type two (DDR2) or type three (DDR3). However, other possibilities exist as well. In this case, the motherboard may be manufactured and distributed with the capability of being upgraded from DDR2 to DDR3 memory in one embodiment. 
         [0006]    The DDR3 memory generally requires support circuitry which is different from that used by DDR2. The reasons for this include the higher density of DDR2, the different supply voltages, the different data rates, and the different packaging arrangements. 
         [0007]    As shown in  FIG. 1 , channel A  16  may include a number of slots  26  that receive DDR3 memories and channel B  18  may include a number of slots  26  that receive DDR2 memories. Detection circuit  28  detects the presence of a dual inline memory module (DIMM) in a slot  26  in either channel A or channel B and, thereby, cause the system to adapt to the particular type of memory being utilized. 
         [0008]    In particular, the memory controller hub pin  12  may be activated to control different memory technologies. The detection circuit  28  asserts the proper chipset straps and redirect necessary signals from the memory controller hub pin  12  to run either in the DDR3 or DDR2 mode. The circuit  28  may also configure the voltage regulator  20  to output the correct voltage levels, either 1.5 volts for DDR3 or 1.8 volts for DDR2. 
         [0009]    While an embodiment is described in which DDR2 or DDR3 is selectively enabled, the present invention is not so limited and may be applied to selectively implementing one of at least two different memory technologies. 
         [0010]    If both DDR2 and DDR3 DIMMs are detected in slots  26 , the detection circuit  28  disables the output power to the memory dual inline memory modules to prevent permanent damage. This would correspond to a mistaken situation where the user inserts both technology types. 
         [0011]    The circuit  28  operates with dual NPN bipolar junction transistors to work as logic NOR gates in one embodiment. The key function of the circuitry is to detect the presence of the dual in line memory modules in the connectors  26 . If one or both of the slots are populated, the output of the dual bipolar junction NPN transistors will be low. If no dual in line memory modules are detected, the output will remain high. Thus, depending on whether the modules are detected in the slots for DDR3 or the slots DDR2, the appropriate controls may be taken care of. 
         [0012]    The memory controller hub pins  12  and  14  may be pins on the same memory controller hub. The pin  12  is an input signal that allows the memory controller hub to track the status of the V_SM power plane. Once a high signal is received, the memory controller hub deasserts a DRAM_RST signal and the DDR3 initialization begins. For DDR2, the pin may be shorted to ground. The pin NOA5 is the one that determines whether there is a DDR2 or a DDR3. It receives a zero for DDR3 and a one for DDR2 in one embodiment. 
         [0013]    Referring to  FIG. 2 , a check at block  40  determines whether the system is on. Then a check at diamond  42  determines whether the circuit  28  has detected a dual inline memory module in one of the sockets  26 . If not, the system does not boot, as indicated in block  44 . An onboard speaker beeps when the end user powers on the board without memory in one embodiment. 
         [0014]    If a dual inline memory module is detected at diamond  42 , then a check at block  46  detects the type of memory inserted. At diamond  48 , it is determined whether, in one embodiment, the memory inserted is DDR2 or DDR3. If it is DDR2, then, in block  50 , NOA5 in the memory controller hub  14  is set equal to H or high Z stage, V_SM is set equal to 1.8 volts in the voltage regulator  20 , and the standard on board voltage regulator V_SM_VTT (not shown) is set equal to 0.9 volts. The regulator V_SM_VTT is set to halve the output of the regulator  20 . Thus, the voltage regulator  20  supplies the 1.8 volt supply used by DDR2. 
         [0015]    Conversely, if DDR3 was detected, then, in block  52 , NOA5 is set equal to L for low V_SM is set equal to 1.5 volts so that the voltage regulator  20  applies the appropriate voltage for DDR3, and V_SM_VTT is set equal to 0.75 volts. In the case where both DDR2 and DDR3 are detected, then, as indicated in block  54 , no boot is allowed. 
         [0016]    The detection circuitry  28  works as follows. If the slots in channel A and B are empty, then NOA5 is left floating, the sense FB is set equal to 1.5 volts and, SS is set equal to zero, as a result, the voltage regulator  20  is shutoff. 
         [0017]    When a DDR2 DIMM is detected, then NOA5 is set equal to zero to turn off the memory controller hub, SS is set equal to the high Z state, and the sense FB is set equal to 1.5 volts so that the voltage regulator  20  outputs 1.5 volts for DDR3. 
         [0018]    Conversely, if. DDR3 is one and DDR2 is zero, then NOA5 is equal to one, SS is in a high Z state, the sense FB voltage is 1.8 volts, and the voltage regulator outputs 1.8 volts for DDR2. 
         [0019]    If both DDR3 and DDR2 are high, then NOA5 is set equal to the indeterminate state, SS is set equal to zero, sense FB is 1.8 volts, and the regulator is shutoff. 
         [0020]    In summary, the output SS is set equal to (  DDR2 *DDR3)+(DDR2*  DDR3 ), FB is set equal to the complement of DDR3 and NOA5 is equal to  DDR2 *DDR3. 
         [0021]    The pin NOA5 at the memory controller hub  14  is a memory controller strap for the DDR2, such that NOA5 equals one for DDR2 and zero for DDR3. The pin DRAM_PWROK at memory controller hub  12  goes high for DDR3, one microsecond after system memory voltage from the voltage regulator  20  is stable. For DDR2, this pin is unused and is tied to ground. 
         [0022]    The SS pin  22  of the voltage regulator serves both as a system memory voltage regulator error amplifier output, as well as for compensation. By pulling this pin low, the voltage regulator output is disabled. The sense pin  24  on the voltage regulator  20  is used to sense the output voltage through a voltage divider and to regulate the output voltage accordingly. 
         [0023]    References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application. 
         [0024]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.