Patent Publication Number: US-10762008-B2

Title: Delay circuit and write and read latency control circuit of memory, and signal delay method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent document claims the priority and benefits of Korean Patent Application No. 10-2017-0160653, filed on Nov. 28, 2017, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The technology and implementations disclosed in this patent document relate to a memory module and a method for operating the memory module. 
     BACKGROUND 
     In various computing devices, systems and applications implementing or using memory for storing digital information, a memory controller may control multiple memory devices connected thereto. The memory controller is connected via internal buses including data buses, address buses, and command buses. The data buses carry data between the memory controller and the multiple memory devices. The address buses and command buses are used to carry address signals and command signals, respectively, from the memory controller to the multiple memory devices. 
     SUMMARY 
     This patent document provides, among others, a technology that may directly exchange data between the memory devices in a memory module. 
     In an embodiment of the disclosed technology, a memory module includes: a first memory device that includes first data pads for communication with a memory controller and second data pads for communication inside the memory module; a second memory device that includes first data pads for communication with the memory controller and second data pads for communication inside the memory module; and an internal data bus suitable for transferring/receiving a data to/from the second data pads of the first memory device and the second data pads of the second memory device, wherein when an internal read command is applied to the first memory device and an internal write command is applied to the second memory device, a data is transferred from the first memory device to the second memory device through the internal data bus. 
     In another embodiment of the disclosed technology, a memory module includes: a plurality of memory devices; a plurality of data buses that respectively correspond to the memory devices and transfer data between each of the memory devices and a memory controller; an internal data bus suitable for transferring data between the memory devices; and a common command bus and a common address bus suitable for controlling the memory devices, wherein each of the memory devices includes: first data pads coupled to the data buses corresponding thereto; and second data pads coupled to the internal data bus, and when an internal read command is applied to a first memory device among the memory devices through the common command bus and the common address bus and an internal write command is applied to a second memory device, a data is transferred between the first memory device and the second memory device through the internal data bus. 
     In another embodiment of the disclosed technology, a method for operating a memory module provided with a first memory device and a second memory device includes: receiving a normal read command in the first memory device and the second memory device; transferring a data from the first memory device to a memory controller through a first memory bus and transferring a data from the second memory device to the memory controller through a second memory bus in response to the normal read command; receiving a normal write command in the first memory device and the second memory device; storing the data transferred from the first memory device through the first memory bus and storing the data transferred from the second memory device through the second memory bus in response to the normal write command; receiving an internal read command in the first memory device; receiving an internal write command in the second memory device; and transferring a data from the first memory device to an internal data bus in response to the internal read command and transferring a data from the second memory device to the internal data bus in response to the internal write command. 
     In another embodiment of the disclosed technology, a memory module includes a first memory device that includes first circuit nodes for communication with a memory controller and second circuit nodes for communication inside the memory module, a second memory device that includes first circuit nodes for communication with the memory controller and second circuit nodes for communication inside the memory module, and an internal data bus that couples the first memory device to the second memory device to carry data between the second circuit nodes of the first memory device and the second circuit nodes of the second memory device. When an internal read command is applied to the first memory device and an internal write command is applied to the second memory device, data is transferred from the first memory device to the second memory device through the internal data bus. 
     In another embodiment of the disclosed technology, a memory module includes a plurality of memory devices, a plurality of data buses, each of which couples one of the plurality of memory devices to a memory controller to carry data between each of the memory devices and the memory controller, an internal data bus that couples the plurality of memory devices to each other to carry data between the memory devices; a common command bus coupled to and shared by the memory devices to direct a common command signal to each of the memory devices to control the memory devices, and a common address bus coupled to and shared by the memory devices to direct a common address signal to each of the memory devices in connection with the common command signal for an operation at each of the memory devices. Each of the memory devices includes: first circuit nodes coupled to the data buses to carry data signals; and second circuit nodes coupled to the internal data bus to carry data signals. When an internal read command is applied to a first memory device among the memory devices through the common command bus and the common address bus and an internal write command is applied to a second memory device, data is transferred between the first memory device and the second memory device through the internal data bus. 
     In another embodiment of the disclosed technology, a method for operating a memory module that includes a first memory device and a second memory device is disclosed. The method includes receiving, at the first memory device and the second memory device, a normal read command, transferring a data from the first memory device to a memory controller through a first memory bus and transferring a data from the second memory device to the memory controller through a second memory bus in response to the normal read command, receiving a normal write command in the first memory device and the second memory device, storing the data transferred from the first memory device through the first memory bus and storing the data transferred from the second memory device through the second memory bus in response to the normal write command, receiving, at the first memory device, an internal read command, receiving, at the second memory device, an internal write command, and transferring data from the first memory device to an internal data bus in response to the internal read command and transferring the data from the internal data bus to the second memory device in response to the internal write command. 
     In another embodiment of the disclosed technology, a method of operating a memory module that includes a plurality of memory devices and an internal data bus carrying data signals between the plurality of memory devices is disclosed. The method includes entering a mode that allows the memory module to select a specific memory device out of a group of memory devices that are selected together in read or write operations, activating a source memory device to load data from the source memory device to the internal data bus, and activating a target memory device to write the data from the internal data bus into the target memory device. 
     In another embodiment of the disclosed technology, a method of operating a memory module that includes a plurality of memory devices and internal data bus carrying data signals between the plurality of memory devices is disclosed. The method includes setting mode registers for each of the plurality of memory devices to be individually activated by masking undesired memory devices from being activated, masking the plurality of memory devices except for source memory devices that load data stored therein into the internal data bus, and masking the plurality of memory devices except for target memory devices that store the data. 
     The above and other embodiments or features of the disclosed technology are described in greater detail in the drawings, the description and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  illustrate an example of a bus connection between a memory controller and memory devices. 
         FIG. 2  is a timing diagram illustrating an example of an operation of a Mode Register Set (MRS) in a Per Dynamic Random Access Memory (DRAM) Addressability (PDA) mode in a memory device. 
         FIG. 3  is a block diagram of an example of a memory system  300  in accordance with an embodiment of the disclosed technology. 
         FIG. 4  is a flowchart describing an example of a process of individually controlling memory devices  320 _ 0  to  320 _ 3  by using a mask command in a memory system  300  shown in  FIG. 3 . 
         FIGS. 5A and 5B  illustrate an example of a process of step  420  shown in  FIG. 4 . 
         FIG. 6  is a block diagram of an example of a memory device  320 _ 0  shown in  FIG. 3 . 
         FIG. 7  is a block diagram of an example of a memory system  700  in accordance with another embodiment of the disclosed technology. 
         FIG. 8  illustrates an example of a process of exchanging data between memory devices  720 _ 1  and  720 _ 3  in a memory module  711  by using an internal read command and an internal write command in the memory system  700  of  FIG. 7  in accordance with an embodiment of the disclosed technology. 
         FIG. 9  illustrates an example of a process of exchanging data between memory devices  720 _ 1  and  720 _ 3  in a memory module  711  by using an internal read command and an internal write command in the memory system  700  of  FIG. 7  in accordance with another embodiment of the disclosed technology. 
         FIG. 10  is a block diagram of an example of a memory device  720 _ 0  shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     The disclosed technology can be implemented to provide a memory system that allows a memory module to individually control a plurality of memory devices in the memory module. 
     In a memory system where different memory devices are controlled by one memory controller, different interfacing configurations between the memory devices and the memory controller may be implemented.  FIGS. 1A and 1B  show two examples. 
       FIG. 1A  shows one example of an interface configuration of a memory system in which a memory controller  100  is provided to control two or more memory devices  110 _ 0  and  110 _ 1  via the interface. This example interface configuration includes a first set of interface buses such as a command bus CMD_BUS_ 0 , an address bus ADD_BUS_ 0 , and a data bus DATA_BUS_ 0  coupled between the memory controller  100  and the first memory device  110 _ 0 , and a second set of interface buses such as a command bus CMD_BUS_ 1 , an address bus ADD_BUS_ 1 , and a data bus DATA_BUS_ 1  coupled between the memory controller  100  and the second memory device  110 _ 1 . This example shows an example for certain implementations where the buses coupled between the memory controller  100  and the first memory device  110 _ 0  are separated from the buses coupled between the memory controller  100  and the second memory device  110 _ 1 , the memory controller  100  may instruct the first memory device  110 _ 0  and the second memory device  110 _ 1  to perform completely separate operations. For example, a write operation may be performed in the second memory device  110 _ 1  while a read operation is being performed in the first memory device  110 _ 0 . 
     However, some implementations may benefit from sharing one or more interface buses for different memory devices such as devices  100 _ 0  and  100 _ 1  while having one or more non-shared interface buses that are respectively designated for individual memory devices, respectively. The specific sharing design for interface buses (e.g., a command bus, an address bus, or a data bus) for different memory devices is dependent on the needs or requirements of a particular memory system.  FIG. 1B  illustrates one example of such implementation different from the interface configuration in  FIG. 1A . In this example, the first memory device  110 _ 0 , which has its own designated data bus DATA_BUS_ 0 , and the second memory device  110 _ 1 , which has its own designated data bus DATA_BUS_ 1 , share common command bus CMD_BUS and address bus ADD_BUS so that the first memory device  110 _ 0  and the second memory device  110 _ 1  may simultaneously perform a read operation or simultaneously perform a write operation in response to the same read or write command carried by the shared command bus CMD_BUS while using their designated data buses to read or write different data. Using the same shared address bus, the memory devices may use the same address for their respectively different data locations. Different from  FIG. 1A , the two memory devices  110 _ 0  and  110 _ 1  are operated in response to the same command and thus may not perform their separate operations independently. For example, the memory controller  100  may not control a read operation to be performed only in the first memory device  110 _ 0 , or may not control a write operation to be performed only in the second memory device  110 _ 1 . 
     A memory rank generally indicates a set of memory chips that are connected to the same chip select and are accessed simultaneously. Some memory control schemes allow programmability of a specific memory chip on a rank by utilizing data strobe signals of each memory chip. For example, Per Dynamic Random Access Memory (DRAM) Addressability (PDA) mode of a memory device can be used to access a specific memory chip instead of accessing all the memory chips in the same memory rank. 
       FIG. 2  is a timing diagram illustrating an example of an operation of a Mode Register Set (MRS) in a PDA mode in a memory device. In various implementations of the disclosed technology, a memory system or module can control various operating modes of the memory chips therein based on data stored in mode registers. During a setting operation such as mode register set operations, the mode registers may store the data for controlling a certain operating mode. 
     The PDA mode may support independent mode register set operations. For example, in the PDA mode, a setting operation may be performed on a desired memory chip or mode register rather than all the memory chips in a memory rank. When memory devices are in the PDA mode, the validity of all the mode resister set commands may be determined according to the signal level of a first data pad DQ 0  which is a circuit node at which a signal is applied (e.g., a voltage) to represent a desired digital logic level (e.g., “1” or “0”). If the signal level of the first data pad DQ 0  is at a logic low level ( 0 ) after the period of a write latency (WL=AL+CWL, where AL represents Additive Latency and CWL represents Column Address Strobe [CAS] Write Latency) has passed from application of a mode register set command, the applied mode register set command may be determined to be valid. If the signal level of the first data pad DQ 0  is at a logic high level ( 1 ), the applied mode register set command may be determined to be invalid, and thus may be ignored. 
     Referring to  FIG. 2 , an MRS command is issued at a moment  201 . If the signal level of the first data pad DQ 0  may transition to the logic low level ( 0 ) before a moment  202  when a write latency (WL=AL+CWL) has passed from the moment  201 , the mode register set command MRS issued at the moment  201  is determined to be valid, and then a corresponding mode register is loaded with application settings based on an address (not shown) and a mode register set command received during a mode register set command cycle time (tMRD_PDA) from the moment  203 . 
     If the signal level of the first data pad DQ 0  is still maintained at the logic high level ( 1 ) up until the moment  202 , the mode register set command MRS issued at the moment  201  may be determined to be invalid, and thus may be ignored. In other words, the corresponding mode register is not loaded. 
       FIG. 3  is a block diagram of an example of a memory system  300  in accordance with an embodiment of the disclosed technology. 
     Referring to  FIG. 3 , the memory system  300  may include a memory controller  310  and a plurality of memory devices  320 _ 0  to  320 _ 3 . Similar to the sharing configuration in  FIG. 1B , the plurality of memory devices  320 _ 0  to  320 _ 3  in  FIG. 3  may share a command bus CMD_BUS and an address bus ADD_BUS. Also similar to  FIG. 1B , the plurality of memory devices  320 _ 0  to  320 _ 3  in  FIG. 3  may be coupled to the memory controller via their designated data buses DATA_BUS_ 0  to DATA_BUS_ 3 , respectively. 
     The command bus CMD_BUS may be used to carry command signals from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3 . Since the memory devices  320 _ 0  to  320 _ 3  share the command bus CMD_BUS, the same command signals may be fed or transferred to the memory devices  320 _ 0  to  320 _ 4 . Examples of the command signals may include an active signal ACT_n, a row address strobe signal RAS_n, a column address strobe signal CAS_n, a write enable signal WE_n, and a chip selection signal CS_n. Additional circuitry such as a buffer circuit may be used for timing adjustment purposes when the command signals are sent on the command bus CMD_BUS. 
     The address bus ADD_BUS may be used to carry address signals from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3 . Since the plurality of memory devices  320 _ 0  to  320 _ 3  share the address bus ADD_BUS, the same address signals may be fed to the plurality of memory devices  320 _ 0  to  320 _ 3 . Examples of the address signals may include a multi-bit bank group address, a multi-bit bank address, and a multi-bit normal address. Additional circuitry such as a buffer circuit may be used for timing adjustment purposes when the address signals are sent on the address bus ADD_BUS. 
     The data buses DATA_BUS_ 0  to DATA_BUS_ 3  may carry multi-bit data between the memory controller  310  and the memory devices  320 _ 0  to  320 _ 3 . Since each memory device has its own data bus, the memory devices  320 _ 0  to  320 _ 3  may send/receive different data to/from the memory controller  310 . 
     The memory controller  310  may control the memory devices  320 _ 0  to  320 _ 3  by using the command bus CMD_BUS and the address bus ADD_BUS and exchange data with the memory devices  320 _ 0  to  320 _ 3  through the data buses DATA_BUS_ 0  to DATA_BUS_ 3 . In an implementation, the memory controller  310  may be included as a part of a processor such as a Central Processing Unit (CPU), a Graphic Processing Unit (GPU), an Application Processor (AP) and the like. In another implementation, the memory controller  310  may be implemented in a memory system or a memory module such as a Dual In-line Memory Module (DIMM). Also, the memory controller  310  may exist in various forms such as a separate chip in an electronic system (e.g., a computing device, a mobile phone, etc.) that includes the memory devices  320 _ 0  to  320 _ 3 . In an implementation of the disclosed technology, the memory controller  310  may use a mask command to individually control the memory devices  320 _ 0  to  320 _ 3 , which will be described below with reference to  FIGS. 4 to 6 . 
     The memory devices  320 _ 0  to  320 _ 3  may share the command bus CMD_BUS and the address bus ADD_BUS. Although the memory devices  320 _ 0  to  320 _ 3  receive the same command signals and address signals from the memory controller  310 , the memory devices  320 _ 0  to  320 _ 3  may perform individual operations by using a mask command, which will be shown with reference to  FIGS. 4 to 6 . Also, although the memory devices  320 _ 0  to  320 _ 3  receive the same command signals and address signals from the memory controller  310 , the memory devices  320 _ 0  to  320 _ 3  may perform individual operations by performing a setting operation on a desired memory chip, which will be described below with reference to  FIGS. 7 and 8 . Each of the memory devices  320 _ 0  to  320 _ 3  may be any type of memory device, such as a DRAM, a Phase Change Random Access Memory (PCRAM), and a flash memory. The memory devices  320 _ 0  to  320 _ 3  may be included in a memory module, such as a dual in-line memory module (DIMM). 
     Although  FIG. 3  shows an example where there are four memory devices  320 _ 0  to  320 _ 3  included in the memory system  300 , it is obvious to those skilled in the art that the number of the memory devices included in the memory system  300  may be different. 
       FIG. 4  is a flowchart describing an example of a process of individually controlling the memory devices  320 _ 0  to  320 _ 3  by using a mask command in the memory system  300  shown in  FIG. 3 . 
     Referring to  FIG. 4 , in an implementation of the disclosed technology, the memory controller  310  in the memory system  300  may set interface terminals (e.g., address pin, data pin, etc.) of a desired memory device out of the memory devices  320 _ 0  to  320 _ 3  such that only signals on a particular interface terminal is recognized as valid, and, at step  420 , the memory controller  310  individually accesses the memory devices  320 _ 0  to  320 _ 3   320 _ 3 . For example, if a certain address bit of a memory device is a “valid” address that is used to select the memory device to execute issued commands, and if the certain address bit of the memory device is “1,” the memory device executes the issued commands. Although the corresponding address bit of other memory devices is “1,” those memory devices ignore the issued commands because the corresponding address bit is not a valid address for them. 
     The memory controller  310 , at step  411 , may control the memory devices  320 _ 0  to  320 _ 3  to enter the Per DRAM Addressability (PDA) mode. This may be carried out by applying, through the command bus CMD_BUS, a combination of the command signals corresponding to the MRS and by applying, through the address bus ADD_BUS, the address signals corresponding to the entering of the PDA mode. 
     At step  412 , the first memory device  320 _ 0  may be set such that a first normal address A 0  thereof is recognized as valid by the first memory device  320 _ 0 . This may be carried out by applying a combination of the command signals corresponding to the MRS and applying a combination of the address signals such that the first normal address A 0  is recognized as valid by the first memory device  320 _ 0 . In addition, after a write latency WL has passed from a moment when an MRS command was issued, the first data pad DQ 0  of the memory device  320 _ 0  is set to “0” by applying the “0” value to the first data bus DATA_BUS_ 0 . Here, the voltage level of the remaining data buses DATA_BUS_ 1  to DATA_BUS_ 3  of the second to fourth memory devices  320 _ 1  to  320 _ 3  remain at low level so that the first data pad DQ 0  of the second to fourth memory devices  320 _ 1  to  320 _ 3  are maintained at “1” to prevent the first normal addresses A 0  of the second to fourth memory devices from being recognized as valid. 
     At step  413 , a second normal address A 1  of the second memory device  320 _ 1  may be set to the predetermined value. At step  414 , a third normal address A 2  of the third memory device  320 _ 2  may be set to the predetermined value. At step  415 , a fourth normal address A 3  of the fourth memory device  320 _ 3  may be set to the predetermined value. The processes of the steps  413  to  415  for setting the address pins of the memory devices  320 _ 1  to  320 _ 3  may be performed in the same manner as the step  412  of setting the address pins of the memory device  320 _ 0 . In an implementation of the disclosed technology, a particular address is regarded as a “valid signal” for a particular memory device, and the valid signal is used to activate only the desired memory device. Although  FIG. 4  shows that the memory devices  320 _ 0  to  320 _ 3  are set such that the first to fourth normal addresses A 0  to A 3  are the valid signals for the memory devices  320 _ 0  to  320 _ 3  to be individually activated, respectively, the scope of this document is not limited thereto. 
     After the memory devices  320 _ 0  to  320 _ 3  are set such that a particular address is regarded as the valid signal for each of the memory devices  320 _ 0  to  320 _ 3  to be individually activated, at step  416  the PDA mode may end. 
     Now, since the memory devices  320 _ 0  to  320 _ 3  are set such that a valid signal of one memory device is different from a valid signal of another memory device, at step  420  the memory controller  310  may individually operate the memory devices  320 _ 0  to  320 _ 3  by using a mask command. The process of the step  420  by which the memory controller  310  individually operates the memory devices  320 _ 0  to  320 _ 3  by using the mask command will be described in detail with reference to  FIGS. 5A and 5B . 
     Various embodiments of the disclosed technology use the mask command to mask some memory devices from executing commands after the mask command is applied. The memory controller  310  may transfer the mask command to the memory devices  320 _ 0  to  320 _ 3  through the command bus CMD_BUS and enable one or more valid signals A 0 , A 1 , A 2  and A 3  of the memory devices  320 _ 0  to  320 _ 3 . Here, the “valid” signal may be an address signal that is used to individually activate each memory device. If a memory device activates its valid signal when the mask command is applied, it will recognize the commands transferred following the mask command as valid commands, whereas if a memory device does not activate its valid signal when the mask command is applied, it will not recognize the commands transferred following the mask command as valid commands. For example, when a valid signal A 2  is enabled when the mask command is applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3 , the commands following the mask command may be executed in the memory device  320 _ 2 , but they may not be executed in the memory devices  320 _ 0 ,  320 _ 1 , and  320 _ 3 . 
     Some of the commands following the mask command may be masked by the mask command, but others of the commands are not masked by the mask command. For example, commands for individually controlling memory devices, such as an active command, a precharge command, a read command, and a write command may be masked by the mask command. In an embodiment of the disclosed technology, those commands may be masked by “masking” data from getting written into undesired memory devices or memory cells. For example, this technique may be implemented by using some of data pins as data mask pins. In another embodiment of the disclosed technology, those commands may be masked by masking command signals or address signals from being applied to the undesired memory devices or memory cells. However, commands for continuously retaining data in a memory device, such as a refresh command, commands for setting a memory device, such as an MRS command, and commands for changing a memory device to be masked, such as another mask command, are not masked by the mask command. Here, the types of the commands to be masked are listed for examples only, and the types of the commands to be masked may vary depending on how a system is designed. 
     In an implementation of the disclosed technology, the mask command may be defined as an unused combination of commands among combinations of command signals. For example, according to a command truth table of JEDEC DDR4 SPEC, a case where a chip selection signal CS_n, an active signal ACT_n, a row address strobe signal RAS_n, a column address strobe signal CAS_n, and a write enable signal WE_n are (L, H, L, H, H) is not defined. This case when these command signals are (L, H, L, H, H) may be defined as a mask command, for example. 
       FIGS. 5A and 5B  illustrate an example of a process of the step  420  shown in  FIG. 4 . 
     Referring to  FIG. 5A , a mask command MSK may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  501 , and the fourth normal address A 3 , which is the valid signal for the fourth memory devices  320 _ 3  to be individually activated, may have a value of “1.” In this way, the first to third memory devices  320 _ 0  to  320 _ 2  excluding the fourth memory device  320 _ 3  may be masked from commands. 
     An active command ACT may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  502 , and an address ADD may be applied to select a particular memory location that will become active in response to the active command ACT. In this way, as shown in  FIG. 5A , the fourth memory device  320 _ 3  becomes active at  502 , whereas the first to third memory devices  320 _ 0  to  320 _ 2  are not activated. 
     A refresh command REF may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  503 , for example. Since the refresh command REF is not masked by the mask command, all of the memory devices  320 _ 0  to  320 _ 3  are refreshed. 
     A write command WT may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  504 , and an address ADD may be applied to select a particular memory location that will store data. In this way, while a write operation is being performed on the fourth memory device  320 _ 3 , the write operation may not be performed on the first to third memory devices  320 _ 0  to  320 _ 2 . 
     A mask command MSK may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  505 , and the third normal address A 2  may have a value of “1.” In this way, the first, second, and fourth memory devices  320 _ 0 ,  320 _ 1  and  320 _ 3  excluding the third memory device  320 _ 2  may be masked from commands. The memory devices masked from the commands by the mask command MSK at the moment  505  may be different from the memory devices masked from the commands by the mask command MSK at the moment  501 . 
     An active command ACT may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  506 , and an address ADD may be applied to select a particular memory location that will become active in response to the active command ACT. In this way, the third memory device  320 _ 2  becomes active at  506 , whereas the first, second, and fourth memory devices  320 _ 0 ,  320 _ 1  and  320 _ 3  are not activated. 
     Referring to  FIG. 5B , a mask command MSK may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  511 , and the first normal address A 0  and the second normal address A 1 , which are the valid addresses of the first and second memory devices  320 _ 0  and  320 _ 1 , respectively, may have a value of “1.” In this way, the third and fourth memory devices  320 _ 2  and  320 _ 3  excluding the first and second memory devices  320 _ 0  and  320 _ 1  may be masked from commands. 
     A read command RD may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  512 , and an address ADD may be applied to read out data from a particular memory location that is selected by the address ADD. In this way, while a read operation is being performed on the memory devices  320 _ 0  and  320 _ 1 , the read operation may not be performed on the memory devices  320 _ 2  and  320 _ 3 . 
     A write command WT may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  513 , and an address ADD may be applied to write data on a particular memory location that is selected by the address ADD. In this way, while a write operation is being performed on the memory devices  320 _ 0  and  320 _ 1 , the write operation may not be performed on the memory devices  320 _ 2  and  320 _ 3 . 
     A mask command MSK is applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  514 , and the third normal address A 2  and the fourth normal address A 3 , which are the valid signals of the third and fourth memory devices  320 _ 2  and  320 _ 3 , may have a value of “1.” In this way, the first and second memory devices  320 _ 0  and  320 _ 1  excluding the third and fourth memory devices  320 _ 2  and  320 _ 3  may be masked from commands. 
     A refresh command REF may be applied from the memory controller  310  to the memory devices  320 _ 0  to  320 _ 3  at a moment  515 . Since the refresh command REF is not masked by the mask command, all of the memory devices  320 _ 0  to  320 _ 3  are refreshed. 
       FIGS. 5A and 5B  show that it is possible to individually operate the memory devices  320 _ 0  to  320 _ 3  which share the command bus CMD_BUS and the address bus ADD_BUS by using the mask command MSK. 
       FIG. 6  is a block diagram of an example of the memory device  320 _ 0  shown in  FIG. 3 . The memory device  320 _ 0  of  FIG. 3  may operate as shown in  FIGS. 4 to 5B . The memory devices  320 _ 0  to  320 _ 3  shown in  FIG. 3  may be the same as or similar to those shown in  FIG. 6 . 
     Referring to  FIG. 6 , the memory device  320 _ 0  may include a command receiving circuit  601 , an address receiving circuit  603 , a data transferring/receiving circuit  605 , a command decoder circuit  610 , a command mask mode control circuit  620 , a setting circuit  630 , and a memory core  640 . 
     The command receiving circuit  601  may receive command signals transferred from the command bus CMD_BUS to circuit nodes CS_n, ACT_n, RAS_n, CAS_n, and WE_n which are command pads in  FIG. 6  since the signal levels at those circuit nodes are digital logic levels of the command signals. In the drawing, the command pads CS_n, ACT_n, RAS_n, CAS_n, and WE_n are represented by the symbols of the command signals received by the corresponding pads. For example, “CS_n” may represent a chip select signal, and “ACT_n” may represent an active signal, and “RAS_n” may represent a row address strobe signal, and “CAS_n” may represent a column address strobe signal. 
     The address receiving circuit  603  may receive address signals transferred from the address bus ADD_BUS to circuit nodes BG 0 , BG 1 , BA 0 , BA 1 , and A 0  to A 14 , which are address pads in  FIG. 6  since the signal levels at those circuit nodes are digital logic levels of the address signals. In  FIG. 6 , the address pads BG 0 , BG 1 , BA 0 , BA 1 , and A 0  to A 14  are represented by the symbols of the address signals received by the corresponding pads. For example, “BG 0 ” and “BG 1 ” may represent bank group address signals, and “BA 0 ” and “BA 1 ” may represent bank address signals, and “A 0 ” to “A 14 ” may represent address signals. 
     The data transferring/receiving circuit  605  may transmit/receive data and data strobe signals via the data bus DATA_BUS_ 0 , the data pads DQ 0  to DQ 3  and the data strobe signal pad DQS 0 . The data strobe signal may be a strobe signal used by the data transferring/receiving circuit  605  to transmit/receive data. 
     The command decoder circuit  610  may decode the command signals received by the command receiving circuit  601  to generate internal command signals IACT, IPCG, IRD, IWT, IREF, IMSK and IMRS. The internal command signals IACT, IPCG, IRD, IWT, IREF, IMSK and IMRS may be enabled when the command signals transferred from the command receiving circuit  601  have combinations corresponding to the commands. The internal command signals may include an internal active signal IACT, an internal precharge signal IPCG, an internal read signal IRD, an internal write signal IWT, an internal refresh signal IREF, an internal mask signal IMSK, an internal MRS signal IMRS and the like. The command decoder circuit  610  may decode the command signals in a normal mode to enable the internal command signal corresponding to a combination of command signals among the internal command signals IACT, IPCG, IRD, IWT, IREF, IMSK, and IMRS, but may not enable the internal active signal IACT, the internal precharge signal IPCG, the internal read signal IRD, and the internal write signal IWT in a mask mode in which the mask mode signal MSK_MODE is enabled. In other words, in the mask mode, the internal command signals IACT, IPCG, IRD, and IWT corresponding to the masked command may not be enabled. Even in the mask mode, the internal command signals IREF, IMSK, and IMRS corresponding to unmasked commands may be enabled normally. 
     In response to the enabling of the internal MRS signal IMRS, the setting circuit  630  may decode an address received by the address receiving circuit  603  and perform various setting operations. The setting circuit  630  may receive the entire part of the address received by the address receiving circuit  603  or may receive only a necessary part of the address. The setting circuit  630  may receive a portion of the data received by the data transferring/receiving circuit  605  to detect the voltage level of the data pad DQ 0  in the PDA mode. What signal, among the signals the memory device  320 _ 0  receives, will be used to individually activate the memory device  320 _ 0  may be set by the setting circuit  630 , and valid signal information INFO_VALID indicating the signals that are used as the “valid signal” may be provided to the command mask mode control circuit  620 . 
     When the address signal that is used as the valid signal, among the address signals received by the address receiving circuit  603 , has a value of “1,” while the internal mask signal IMSK is enabled, the mask mode control circuit  620  may control the command decoder circuit  610  in the normal mode. In other words, the mask mode signal MSK_MODE may be maintained in a disabled state. Also, when the address signal that is used as the valid signal, among the address signals received by the address receiving circuit  603 , has a value of “0,” while the internal mask signal IMSK is enabled, the mask mode control circuit  620  may control the command decoder circuit  610  in the command mask mode. In other words, the mask mode signal MSK_MODE may be enabled. As described above, the command decoder circuit  610  may not enable the masked internal command signals IACT, IPCG, IRD and IWT, when the mask mode signal MSK_MODE is enabled. 
     The memory core  640  may perform an active operation, a precharge operation, a refresh operation, a read operation, and a write operation, which are main operations of the memory device  320 _ 0 . The memory core  640  may include a cell array, a row circuit for controlling an active operation, a precharge operation and a refresh operation of the cell array, and a column circuit for controlling a read operation and a write operation of the cell array. The memory core  640  may perform operations corresponding to the enabled internal command signals among the internal command signals IACT, IPCG, IRD, IWT and IREF. The memory core  640  may receive the address received by the address receiving circuit  603  to perform an operation requiring an address, such as an active operation, a read operation, a write operation and the like. Also, the data that is read from the memory core  640  during a read operation may be read out through the data bus DATA_BUS_ 0  and the data transferring/receiving circuit  605 , and the data to be written to the memory core  640  during a write operation may be received through the data bus DATA_BUS_ 0  and the data transferring/receiving circuit  605 . 
       FIG. 7  is a block diagram of an example of a memory system  700  in accordance with another embodiment of the disclosed technology. 
     Referring to  FIG. 7 , the memory system  700  may include a memory controller  710  and a memory module  711 . The memory module  711  may include a plurality of memory devices  720 _ 0  to  720 _ 3 . The plurality of memory devices  720 _ 0  to  720 _ 3  may share a command bus CMD_BUS and an address bus ADD_BUS. Also, separate data buses DATA_BUS_ 0  to DATA_BUS_ 3  may be allocated to the memory devices  720 _ 0  to  720 _ 3 , respectively. In an implementation of the disclosed technology, the memory module  711  may further include an internal data bus DATA_BUS_INT for carrying data between the memory devices  720 _ 0  to  720 _ 3 . Here, the internal data bus DATA_BUS_INT may also be shared by the plurality of memory devices  720 _ 0  to  720 _ 3 . The memory module  711  may be of a Dual In-line Memory Module (DIMM) type. 
     The command bus CMD_BUS may be used to carry command signals from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3 . Since the memory devices  720 _ 0  to  720 _ 3  share the command bus CMD_BUS, the same command signals may be fed to the memory devices  720 _ 0  to  720 _ 4 . Examples of the command signals may include an active signal ACT_n, a row address strobe signal RAS_n, a column address strobe signal CAS_n, a write enable signal WE_n, and a chip selection signal CS_n. The memory module  711  may further include a buffer circuit for buffering command signals on the command bus CMD_BUS and timing adjustment of the command signals. 
     The address bus ADD_BUS may be used to carry address signals from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3 . Since the plurality of memory devices  720 _ 0  to  720 _ 3  share the address bus ADD_BUS, the same address signals may be fed to the plurality of memory devices  720 _ 0  to  720 _ 3 . Examples of the address signals may include a multi-bit bank group address, a multi-bit bank address, and a multi-bit normal address. Additional circuitry such as a buffer circuit may be used for timing adjustment purposes when the address signals are sent on the address bus ADD_BUS. 
     The data buses DATA_BUS_ 0  to DATA_BUS_ 3  may carry multi-bit data between the memory controller  710  and the plurality of memory devices  720 _ 0  to  720 _ 3 . Since each memory device has its own data bus, the plurality of memory devices  720 _ 0  to  720 _ 3  may send/receive different data to/from the memory controller  710 . The memory module  711  may further include buffer circuits for buffering data on the data buses DATA_BUS_ 0  to DATA_BUS_ 3  and timing adjustment of the data. 
     The internal data bus DATA_BUS_INT is a data bus for exchanging data between the memory devices  720 _ 0  to  720 _ 3  in the memory module  711  and may be shared by the plurality of memory devices  720 _ 0  to  720 _ 3 . The memory devices  720 _ 0  to  720 _ 3  may use the data buses DATA_BUS_ 0  to DATA_BUS_ 3  and/or the internal data bus DATA_BUS_INT during a read operation and a write operation. For example, the memory device  720 _ 2  may use the data bus DATA_BUS_ 2  during the read operation or the write operation to carry data to or from the memory controller  710 , and may use the internal data bus DATA_BUS_INT during the read and write operations to carry data to or from another memory device, e.g., the memory device  720 _ 0 , in the memory module  711 . 
     The memory controller  710  may control the plurality of memory devices  720 _ 0  to  720 _ 3  by using the command bus CMD_BUS and the address bus ADD_BUS, and may exchange data with the memory devices  720 _ 0  to  720 _ 3  through the data buses DATA_BUS_ 0  to DATA_BUS_ 3 . In an implementation of the disclosed technology, the memory controller  710  may be included as a part of a processor such as a Central Processing Unit (CPU), a Graphic Processing Unit (GPU), an Application Processor (AP) and the like. In another implementation, the memory controller  710  may be implemented as a separate chip in a system (e.g., a computing device, a mobile phone, etc.) including the plurality of memory devices  720 _ 0  to  720 _ 3 . As described earlier with reference to  FIGS. 4 to 6 , the memory controller  710  may use a mask command to individually control the plurality of memory devices  720 _ 0  to  720 _ 3 . Also, the memory controller  710  may directly transfer data from one memory device to another memory device in the memory module without reading out data to the memory controller  710  in order to write the read-out data into another memory device in the memory module. In an implementation of the disclosed technology, the memory controller  710  may use an internal read command for directing the memory devices  720 _ 0  to  720 _ 3  to perform an internal read operation by using an internal data bus, and may use an internal write command for directing the memory devices  720 _ 0  to  720 _ 3  to perform an internal write operation by using an internal data bus. The internal read/write operations may be controlled by specially defined command signals. Alternatively, the internal read/write operations may be controlled by using normal read/write commands if the memory devices can distinguish these commands from those for normal read/write operations. For example, when a memory device receive read/write commands along with a certain signal that indicates the received read/write commands are for the internal read/write operations, it can internally transfer data between two different memory devices in the memory module via an internal data bus DATA_BUS_INT. The internal read/write operations may include the exchange of data between two memory devices in the memory module, which will be described in detail later with reference to  FIGS. 8 to 10 . 
     The plurality of memory devices  720 _ 0  to  720 _ 3  may share the command bus CMD_BUS and the address bus ADD_BUS. Although the memory devices  720 _ 0  to  720 _ 3  receive the same command signals and address signals from the memory controller  710 , the memory devices  720 _ 0  to  720 _ 3  may perform individual operations by using a mask command, which is described with reference to  FIGS. 4 to 6 . The memory devices  720 _ 0  to  720 _ 3  may perform a read operation and a write operation by using the data buses DATA_BUS_ 0  to DATA_BUS_ 3  during a normal read operation and a normal write operation, and may perform a read operation and a write operation by using the internal data bus DATA_BUS_INT during an internal read operation and an internal write operation. The internal read operation and the internal write operation will be shown with reference to  FIGS. 8 to 10 . In an implementation of the disclosed technology, the internal read operation of the memory devices  720 _ 0  to  720 _ 3  may be controlled by the internal read command, and the internal write operation may be controlled by the internal write command. Each of the memory devices  720 _ 0  to  720 _ 3  may be any type of memory device, such as a Dynamic Random Access Memory (DRAM), a Phase Change Random Access Memory (PCRAM), and a flash memory. 
     In an implementation of the disclosed technology, the internal read command may be a special command signal used to set the internal data bus DATA_BUS_INT as an active data bus that will be used by the memory devices  720 _ 0  to  720 _ 3  when the memory devices  720 _ 0  to  720 _ 3  perform a read operation. The internal write command may be another special command signal used to set the internal data bus DATA_BUS_INT as an active data bus that will be used by the memory devices  720 _ 0  to  720 _ 3  when the memory devices  720 _ 0  to  720 _ 3  perform a write operation. In another implementation of the disclosed technology, the internal read command may be a normal read command that is applied to the memory devices  720 _ 0  to  720 _ 3  after the internal data bus DATA_BUS_INT has been set as an active data bus that is used by the memory devices  720 _ 0  to  720 _ 3 . Also, the internal write command may be a normal write command that is applied to the memory devices  720 _ 0  to  720 _ 3  after the internal data bus DATA_BUS_INT has been set as an active data bus that is used by the memory devices  720 _ 0  to  720 _ 3 . 
     Although  FIG. 7  shows an example where there are four memory devices  720 _ 0  to  720 _ 3  in the memory module  711 , it is obvious to those skilled in the art that the number of the memory devices in the memory module  711  may vary depending on what application the memory module  711  is used for. 
       FIG. 8  illustrates an example of a process of internally transferring data between memory devices  720 _ 1  and  720 _ 3  in the memory module  711  by using an internal read command and an internal write command in the memory system  700  of  FIG. 7  based on an embodiment of the disclosed technology. Prior to the operation shown in  FIG. 8 , the processes of the steps  411  to  416  shown in  FIG. 4  may be performed to set a “valid” signal for individually controlling the memory devices  720 _ 0  to  720 _ 3 . Also, before the operation of  FIG. 8  is performed, the memory devices  720 _ 0  to  720 _ 3  may perform a normal write operation and a normal read operation. 
     Referring to  FIG. 8 , a mask command MSK may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  801 , and the second normal address A 1 , which is the valid signal for the memory device  720 _ 1  to be individually activated, may have a value of “1.” In this way, the first, third, and fourth memory devices  720 _ 0 ,  720 _ 2 , and  720 _ 3  excluding the second memory device  720 _ 1  may be masked from commands. 
     An active command ACT may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  802 , and an address ADD may be applied to select a particular memory location that will become active in response to the active command ACT. In this way, the memory device  720 _ 1  becomes active at  802 . 
     A mask command MSK may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  803 , and a fourth normal address A 3 , which is the valid signal for the memory devices  720 _ 3  to be individually activated, may have a value of “1.” In this way, the first to third memory devices  720 _ 0  to  720 _ 2  excluding the fourth memory device  720 _ 3  may be masked from commands. 
     An active command ACT may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  804 , and an address ADD may be applied to select a particular memory location that will become active in response to the active command ACT. In this way, the fourth memory device  720 _ 3  becomes active at  804 . 
     An internal read command RD_I may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  805 , and an address ADD may be applied to select a particular memory location on which the internal read operation is performed. In this way, the fourth memory device  720 _ 3  gets ready for the internal read operation. The internal read command RD_I may be distinguished from the normal read command by setting the value of a certain distinguishable address bit (e.g., A 14 ) of the address ADD, which is not used during the read operation, to “1,” for example. During the read operation, a smaller number of address bits are used as compared to that in the active operation. For example, normal address signals of 15 bits (e.g., A 0  to A 14 ) may be used during an active operation (e.g., a row operation). However, during a read operation and a write operation (e.g., column operations), normal address signals of 10 bits (e.g., A 0  to A 9 ) may be used. The internal read command RD_I and the normal read command RD may be distinguished from each other by applying a predetermined voltage (e.g., “1”) as the normal address signal A 14 , which is not used in the read operation. 
     A mask command MSK may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  806 , and the second normal address A 1 , which is the valid signal for the memory devices  720 _ 1  to be individually activated, may have a value of “1.” In this way, the first, third, and fourth memory devices  720 _ 0 ,  720 _ 2  and  720 _ 3  excluding the second memory device  720 _ 1  may be masked from commands. 
     An internal write command WT_I may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  807 , and an address ADD may be applied to select a particular memory location on which the internal write operation is performed. In this way, the second memory device  720 _ 1  gets ready for the internal write operation. The internal write command WT_I may be distinguished from the normal write command by setting the value of a certain distinguishable address bit (e.g., A 14 ) of the address ADD, which is not used during the write operation, to “1,” for example. 
     Data may be outputted from the memory device  720 _ 3  to the internal data bus DATA_BUS_INT at a moment  808  when a read latency RL has passed from the moment  805  (when a write latency WL has passed from the moment  807 ). As an example,  FIG. 8  illustrates a timing diagram where eight data bits D 0  to D 7  are consecutively outputted because a burst length BL is eight “8.” Therefore, from the moment  808 , the memory device  720 _ 1  may receive and store the data from the internal data bus DATA_BUS_INT. Here, the read latency RL may indicate the time it takes to read the first piece of data out of a desired memory cell after the registration of a read command, and the write latency WL may indicate the time it takes to write the first piece of data into a desired memory cell after the registration of a write command. Those schemes discussed above are based on the fact that the read latency RL is longer than the write latency WL. 
     To exchange or transfer data between the fourth memory device  720 _ 3  and the second memory device  720 _ 1 , an input timing of the data D 0  to D 7  from the memory device  720 _ 3  to the internal data bus DATA_BUS_INT can be set to coincide with an output timing of the data D 0  to D 7  from the internal data bus DATA_BUS_INT to the memory device  720 _ 1 . Therefore, the internal write command WT_I is applied to the memory device  720 _ 1  at the moment  807  when the time “RL-WL” has passed since the internal read command RD_I was applied to the memory device  720 _ 3  at  805 . 
     As can be seen from  FIG. 8 , data may be directly transferred between the memory devices  720 _ 1  and  720 _ 3  in the memory module  711  by using the internal data bus DATA_BUS_INT on the memory module  711 . 
       FIG. 9  illustrates an example of a process of internally transferring data between memory devices  720 _ 1  and  720 _ 3  in the memory module  711  by using an internal read command and an internal write command in the memory system  700  of  FIG. 7  based on another embodiment of the disclosed technology. Prior to the operation shown in  FIG. 9 , the processes of the steps  411  to  416  shown in  FIG. 4  may be performed to set a “valid” signal for individually controlling the memory devices  720 _ 0  to  720 _ 3 . Also, before the operation of  FIG. 9  is performed, the memory devices  720 _ 0  to  720 _ 3  may perform a normal write operation and a normal read operation. 
     Referring to  FIG. 9 , an active command ACT may be given from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  901 , and an address ADD may be applied to select a particular memory location that will become active in response to the active command ACT. In this way, the memory devices  720 _ 0  to  720 _ 3  become active. 
     A mask command MSK may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  902 , and a fourth normal address A 3 , which is the valid signal for the fourth memory devices  720 _ 3  to be individually activated, may have a value of “1.” In this way, the first to third memory devices  720 _ 0  to  720 _ 2  excluding the fourth memory device  720 _ 3  may be masked from commands. 
     An internal read command RD_I may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  903 , and an address ADD may be applied to select a particular memory location on which the internal read operation is performed. In this way, the fourth memory device  720 _ 3  is now ready for the internal read operation. 
     A mask command MSK may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  904 , and the second normal address A 1 , which is the valid signal for the second memory devices  720 _ 1  to be individually activated, may have a value of “1.” In this way, the first, third, and fourth memory devices  720 _ 0 ,  720 _ 2  and  720 _ 3  excluding the second memory device  720 _ 1  may be masked from commands. 
     An internal write command WT_I may be applied from the memory controller  710  to the memory devices  720 _ 0  to  720 _ 3  at a moment  905 , and an address ADD may be applied to select a particular memory location on which the internal write operation is performed. In this way, the second memory device  720 _ 1  is now ready for the internal write operation. 
     Data may be outputted from the memory device  720 _ 3  to the internal data bus DATA_BUS_INT at a moment  906  when a read latency RL has passed from the moment  903  (when the write latency WL has passed from the moment  905 ). Therefore, from the moment  906 , the memory device  720 _ 1  may receive and store the data from the internal data bus DATA_BUS_INT. 
     As can be seen from  FIG. 9 , the internal write command WT_I is applied to the memory device  720 _ 1  at the moment  905  when the time “RL-WL” has passed since the internal read command RD_I was applied to the memory device  720 _ 3  at  903 . 
       FIG. 9  also shows that the process of simultaneously enabling the memory devices  720 _ 0  to  720 _ 3  and transferring data between the memory devices  720 _ 0  to  720 _ 3  is simpler than the process of  FIG. 8 . Since the memory devices  720 _ 0  to  720 _ 3  are simultaneously enabled, data may be transferred only in the same row of the memory devices  720 _ 0  to  720 _ 3 . 
       FIG. 10  is a block diagram of an example of the memory device  720 _ 0  shown in  FIG. 7 . The memory device  720 _ 0  of  FIG. 10  may operate as shown in  FIGS. 8 and 9 . The memory devices  720 _ 1  to  720 _ 3  of  FIG. 7  may also be the same as or similar to those of  FIG. 10 . 
     Referring to  FIG. 10 , the memory device  720 _ 0  may include a command receiving circuit  1001 , an address receiving circuit  1003 , a first data transferring/receiving circuit  1005 _ 0 , a second data transferring/receiving circuit  1005 _ 1 , a command decoder circuit  1010 , a command mask mode control circuit  1020 , a setting circuit  1030 , a memory core  1040 , a selection signal generation circuit  1050 , and a selection circuit  1060 . 
     The command receiving circuit  1001  may receive command signals transferred from the command bus CMD_BUS to the command pads CS_n, ACT_n, RAS_n, CAS_n and WE_n. In the drawing, the command pads CS_n, ACT_n, RAS_n, CAS_n and WE_n are represented by symbols of command signals received by the corresponding pads. For example, “CS_n” may represent a chip selection signal, and “ACT_n” may represent an active signal, and “RAS_n” may represent a row address strobe signal, and “CAS_n” may represent a column address strobe signal. 
     The address receiving circuit  1003  may receive address signals transferred from the address bus ADD_BUS to address pads BG 0 , BG 1 , BA 0 , BA 1 , and A 0  to A 14 . In the drawing, the address pads BG 0 , BG 1 , BA 0 , BA 1 , and A 0  to A 14  are represented by the symbols of the address signals received by the corresponding pads. To be specific, “BG 0 ” and “BG 1 ” may represent bank group address signals, and “BA 0 ” and “BA 1 ” may represent bank address signals, and “A 0 ” to “A 14 ” may represent address signals. 
     The first data transferring/receiving circuit  1005 _ 0  may transmit/receive data and data strobe signals via the data bus DATA_BUS_ 0  through data pads DQ 0  to DQ 3  and a data strobe signal pad DQS 0 . The first data transferring/receiving circuit  1005 _ 0  may be enabled during a normal read operation and a normal write operation to transmit/receive data to/from the data bus DATA_BUS_ 0 . The selection signal SEL may be a signal for enabling/disabling the first data transferring/receiving circuit  1005 _ 0 , and the first data transferring/receiving circuit  1005 _ 0  may be enabled when the selection signal SEL is disabled. 
     The second data transferring/receiving circuit  1005 _ 1  may transmit/receive data and data strobe signals with the data bus DATA_BUS_ 0  through data pads DQ 4  to DQ 7  and a data strobe signal pad DQS 1 . The second data transferring/receiving circuit  1005 _ 1  may be enabled during a normal read operation and a normal write operation to transmit/receive data to/from the internal data bus DATA_BUS_INT. The selection signal SEL may be a signal for enabling/disabling the second data transferring/receiving circuit  1005 _ 1 , and the second data transferring/receiving circuit  1005 _ 1  may be enabled when the selection signal SEL is enabled. 
     The selection circuit  1060  may select a data transferring/receiving circuit for transferring/receiving data to/from the memory core  1040  in response to the selection signal SEL. When the selection signal SEL is disabled, the first data transferring/receiving circuit  1005 _ 0  may be selected to exchange data with the memory core  1040 . When the selection signal  1060  is enabled, the second data transferring/circuit  1005 _ 1  may be selected to exchange data with the memory core  1040 . 
     The command decoder circuit  1010  may decode the command signals received by the command receiving circuit  1001  to generate internal command signals IACT, IPCG, IRD, IWT, IREF, IMSK and IMRS. The internal command signals IACT, IPCG, IRD, IWT, IREF, IMSK and IMRS may be enabled, when the command signals transferred from the command receiving circuit  1001  have combinations corresponding to the commands. The internal command signals may include an internal active signal IACT, an internal precharge signal IPCG, an internal read signal IRD, an internal write signal IWT, an internal refresh signal IREF, an internal mask signal IMSK, an internal MRS signal IMRS and the like. The command decoder circuit  610  may decode the command signals in a normal mode to enable the internal command signal corresponding to a combination of command signals among the internal command signals IACT, IPCG, IRD, IWT, IREF, IMSK, and IMRS, but may not enable the internal active signal IACT, the internal precharge signal IPCG, the internal read signal IRD, and the internal write signal IWT in a mask mode in which the mask mode signal MSK_MODE is enabled. In other words, in the mask mode, the internal command signals IACT, IPCG, IRD, and IWT corresponding to the masked command may not be enabled. Even in the mask mode, the internal command signals IREF, IMSK, and IMRS corresponding to unmasked commands may be enabled normally. 
     In response to the enabling of the internal MRS signal IMRS, the setting circuit  1030  may decode an address received by the address receiving circuit  1003  and perform various setting operations. The setting circuit  1030  may receive the entire part of the address received by the address receiving circuit  1003  or may receive only a necessary part of the address. The setting circuit  1030  may receive a portion of the data received by the data transferring/receiving circuit  1005  to detect the voltage level of the data pad DQ 0  in the PDA mode. What signal, among the signals the memory device  720 _ 0  receives, will be used to individually activate the memory device  720 _ 0  may be set by the setting circuit  1030 , and valid signal information INFO_VALID indicating the signals that are used as the “valid signal” may be provided to the command mask mode control circuit  1020 . 
     When the address signal that is used as the valid signal, among the address signals received by the address receiving circuit  1003 , has a value of “1,” while the internal mask signal IMSK is enabled, the mask mode control circuit  1020  may control the command decoder circuit  1010  in the normal mode. In other words, the mask mode signal MSK_MODE may be maintained in a disabled state. Also, when the address signal that is used as the valid signal, among the address signals received by the address receiving circuit  1003 , has a value of “0,” while the internal mask signal IMSK is enabled, the mask mode control circuit  1020  may control the command decoder circuit  1010  in the command mask mode. In other words, the mask mode signal MSK_MODE may be enabled. As described above, the command decoder circuit  1010  may not enable the masked internal command signals IACT, IPCG, IRD and IWT, when the mask mode signal MSK_MODE is enabled. 
     The memory core  1040  may perform an active operation, a precharge operation, a refresh operation, a read operation, and a write operation, which are main operations of the memory device  720 _ 0 . The memory core  1040  may include a cell array, a row circuit for controlling an active operation, a precharge operation and a refresh operation of the cell array, and a column circuit for controlling a read operation and a write operation of the cell array. The memory core  1040  may perform operations corresponding to the enabled internal command signals among the internal command signals IACT, IPCG, IRD, IWT and IREF. The memory core  1040  may receive the address received by the address receiving circuit  1003  to perform an operation requiring an address, such as an active operation, a read operation, a write operation and the like. Also, the memory core  1040  may transfer/receive data through the selected data transferring/receiving circuit among the data transferring/receiving circuits  1005 _ 0  and  1005 _ 1  during the read and write operations. 
     The selection signal generation circuit  1050  may generate a selection signal SEL in response to the logical level of the address signal A 14  among the address signals received by the address reception circuit  1003 , when the internal read signal IRD or the internal write signal IWT is enabled. For example, when the address bit A 14  has a value of “1” while the internal read signal IRD is enabled, the selection signal SEL may be enabled to “1,” and when the address bit A 14  has a value of “0” while the internal read signal IRD is enabled, the selection signal SEL may be disabled to “0.” 
     In an embodiment of the disclosed technology, a method of operating a memory module that includes a plurality of memory devices and internal data bus carrying data signals between the plurality of memory devices may include entering a mode that allows the memory module to select a specific memory device out of a group of memory devices that are selected together in read or write operations, activating source memory devices to load data from the source memory devices to the internal data bus, and activating target memory devices to write the data from the internal data bus into the target memory devices. Here, the mode is implemented by using unused address pins of the plurality of memory devices such that each of the plurality of memory devices is selected by one of the unused address pins. 
     In another embodiment of the disclosed technology, a method of operating a memory module that includes a plurality of memory devices and internal data bus carrying data signals between the plurality of memory devices may include setting mode registers for each of the plurality of memory devices to be individually activated by masking undesired memory devices from being activated, masking the plurality of memory devices except for source memory devices that load data stored therein into the internal data bus, and masking the plurality of memory devices except for target memory devices that store the data. 
     According to the embodiments of the disclosed technology, data may be directly transferred between the memory devices in the memory module without reading out the data. 
     While the disclosed technology has been described with respect to the specific embodiments, various changes and modifications may be made based on what is disclosed and illustrated.